# Patent

## Title
Parasite detection via endosymbiont detection

## Abstract

The present invention provides systems, methods, and compositions for identifying a subject as infected with a parasite by detecting nucleic acid from an endosymbiont of the parasite in a sample from the subject. In certain embodiments, the parasite is a nematode that infects humans or dogs (e.g., D. immitis, O. volvulus, W. bancrofti, B. timori, or B. malayi) and the endosymbiont is Wolbachia.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present Application claims priority to PCT Application No. PCT/US2011/028148, filed Mar. 11, 2011 and U.S. Provisional Application Ser. No. 61/131,751, filed Mar. 14, 2010, the entirety of each of which is herein incorporated by reference.


SEQUENCE LISTING
The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 22, 2011, is named 10373US1.txt and is 2,778 bytes in size.
FIELD OF THE INVENTION
The present invention provides systems, methods, and compositions for identifying a subject or sample as infected with a parasite by detecting biomolecules (e.g., nucleic acid) from an endosymbiont of the parasite in a sample from the subject. In certain embodiments, the parasite is a nematode that infects humans or dogs (e.g., D. immitis, O. volvulus, W. bancrofti, B. timori, or B. malayi) and the endosymbiont is Wolbachia. 
BACKGROUND OF THE INVENTION
Dirofilaria immitis (Heartworm) is a parasitic roundworm that is spread from host to host through the bites of mosquitoes. The heartworm is a type of filaria, a small thread-like worm. The definitive host is the dog but it can also infect cats, wolves, coyotes, foxes and other animals, such as ferrets, sea lions and even, under rare circumstances, humans. The parasite is commonly called “heartworm” because the adult reproductive stage of its life cycle resides primarily in the right ventricle of its host where it can live for many years. Heartworm infection may result in serious disease for the host. Wolbachia in an endosymbiont of D. immitis. 
Onchocerca volvulus is a nematode that causes Onchocerciasis or “River Blindness” mostly in Africa. Long-term corneal inflammation, or keratitis, leads to thickening of the corneal stroma which ultimately leads to blindness. Humans are the only definitive host for O. volvulus. The intermediate host or vector is the Black fly (Simulium spp.). O. volvulus, along with most nematodes, share an endosymbiotic relationship with the bacterium Wolbachia spp. In the absence of Wolbachia, larval development of the O. volvulus is disrupted or ceased.
Brugia malayi is a roundworm nematode, one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower limbs. The two other filarial causes of lymphatic filariasis are Wuchereria bancrofti and Brugia timori, which differ from B. malayi morphologically, symptomatically, and in geographical extent. B. malayi is transmitted by mosquitoes and is restricted to South and South East Asia. It is one of the tropical diseases targeted for elimination by the year 2020 by the World Health Organization. Wolbachia in an endosymbiont of B. malayi. 
Wuchereria bancrofti is a parasitic filarial nematode worm spread by a mosquito vector. It is one of the three parasites that cause lymphatic filariasis, an infection of the lymphatic system by filarial worms. It affects over 120 million people, primarily in Africa, South America, and other tropical and sub-tropical countries. If the infection is left untreated it can develop into a chronic disease called Elephantiasis. Wolbachia in an endosymbiont of W. bancrofti. 
Brugia timori is a human filarial parasite which causes the disease “Timor filariasis.” Anopheles barbirostris is the primary vector for this parasite. Like other human filariasis infections, Brugia timori filariasis causes acute fever and chronic lymphedema. The life cycle of Brugia timori is very similar to that of Wuchereria bancrofti and Brugia malayi, leading to nocturnal periodicity of the disease symptoms. Wolbachia in an endosymbiont of B. timori. 
What is needed are non-invasive methods for detecting the presence of parasites in a subject, such as the parasites mentioned above.
SUMMARY OF THE INVENTION
The present invention provides systems, methods, and compositions for identifying a subject or sample as infected with a parasite by detecting biomolecules (e.g., nucleic acid) from an endosymbiont of the parasite in a sample from the subject. In certain embodiments, the parasite is a nematode that infects humans or dogs (e.g., D. immitis, O. volvulus, W. bancrofti, B. timori, or B. malayi) and the endosymbiont is Wolbachia. In particular embodiments, detection of the endosymbiont employs at least one primer pair specific for the endosymbiont.
In some embodiments, the present invention provides methods of identifying a parasite in a source (e.g., subject, biological sample from a subject, etc.), comprising: a) providing: i) a sample from a source suspected of being infected with a parasite, wherein the parasite is associated with an endosymbiont; and ii) a nucleic acid detection assay configured to detect nucleic acid from the endosymbiont; b) contacting the sample with the nucleic acid detection assay under conditions such that the presence or absence of the endosymbiont in the sample is determined, wherein the presence of the endosymbiont identifies the source as being infected with the parasite.
In certain embodiments, the source is a subject and the methods further comprise a step of diagnosing the subject as being infected with the parasite based on the presence of the endosymbiont in the sample. In further embodiments, the diagnosing is accomplished without directly detecting the presence of the parasite in the source (e.g., the endosymbiont serves as a proxy for the presence of the parasite in the source). In other embodiments, the nucleic acid detection assay comprises at least one primer pair, and the contacting generates endosymbiont amplicons using the primer pair under amplification conditions.
In some embodiments, the methods further comprise a step of determining at least a partial base count of at least a subsequence of the endosymbiont amplicons to produce base count data. In other embodiments, the methods further comprise querying a database comprising at least one base count entry corresponding to an identified nucleic acid to produce a match of the base count data with the base count entry, thereby identifying the endosymbiont amplicon as from the endosymbiont. In certain embodiments, determining at least a partial base count employs mass spectrometry. In other embodiments, determining at least a partial base count does not employ mass spectrometry (e.g., sequencing or other methodology is employed). In further embodiments, the nucleic acid detection assay employs any one or more of (or consists of): a TAQMAN assay, a sequencing assay, a polymerase chain reaction assay, a hybridization assay, a microarray assay, a bead array assay, a primer extension assay, an enzyme mismatch cleavage assay, a branched hybridization assay, a rolling circle replication assay, a NASBA assay, a molecular beacon assay, a cycling probe assay, a ligase chain reaction assay, a sandwich hybridization assay, an INVADER assay, and a Line Probe Assay.
In particular embodiments, the present invention provides systems comprising: a) a sample from a subject suspected of being infected with a parasite, wherein the parasite is associated with an endosymbiont; and b) a nucleic acid detection assay configured to detect nucleic acid from the endosymbiont.
In particular embodiments, the parasite is a nematode. In further embodiments, the nematode infects dogs or cats. In other embodiments, the nematode infects humans. In certain embodiments, the nematode is selected from Table 1. In some embodiments, the endosymbiont is a Wolbachia species (e.g., a Wolbachia species associated with Dirofilaria immitis, Onchocerca volvulus, Wuchereria bancrofti, Brugia timori, or Brugia malayi). In further embodiments, the parasite is selected from the group consisting of: Dirofilaria immitis, Onchocerca volvulus, Wuchereria bancrofti, Brugia timori, and Brugia malayi. 
In other embodiments, the nucleic acid detection assay comprises at least one primer pair, wherein the primer pair includes one or more, or consists of: SEQ ID NOs:1 and 2; SEQ ID NOs:3 and 4; SEQ ID NOs:5 and 6; SEQ ID NOs:7 and 8; and SEQ ID NOs:9 and 10. In some embodiments, the nucleic acid detection assay comprises at least one primer pair, wherein the primer pair is configured to hybridize with conserved regions of the endosymbiont nucleic acid that flank a variable region of the endosymbiont nucleic acid.
In certain embodiments, the present invention provides compositions comprising at least one purified oligonucleotide primer pair that comprises forward and reverse primers, wherein the primer pair comprises nucleic acid sequences that are substantially complementary to a nucleic acid sequence from an endosymbiont, wherein the primer pair is configured to hybridize with conserved regions of the nucleic acid from the endosymbiont that flank variable regions of the nucleic acid from the endosymbiont.
In other embodiments, the forward and reverse primers are about 15 to 35 nucleobases in length, and wherein the forward primer comprises at least 70% sequence identity (e.g., 70% . . . 80% . . . 90% . . . 95% . . . 99% sequence identity) with a sequence selected from the group consisting of SEQ ID NOS: 1, 3, 5, 7, and 9, and the reverse primer comprises at least 70% sequence identity (e.g., 70% . . . 80% . . . 90% . . . 95% . . . 99% sequence identity) with a sequence selected from the group consisting of SEQ ID NOS: 2, 4, 6, 8, and 10.
In some embodiments, the primer pair is selected from the group of primer pair sequences consisting of: SEQ ID NOS: 1:2, 3:4, 5:6, 7:8, and 9:10. In further embodiments, the primer pair is configured to generate amplicons that are 45 to 200 nucleobases in length. In other embodiments, the forward and/or reverse primer comprises at least one molecular mass modifying tag. In particular embodiments, the forward and/or reverse primer comprises at least one modified nucleobase. In other embodiments, the modified nucleobase is 5-propynyluracil or 5-propynylcytosine. In some embodiments, the modified nucleobase is a mass modified nucleobase. In further embodiments, the mass modified nucleobase is 5-Iodo-C. In additional embodiments, the modified nucleobase is a universal nucleobase. In some embodiments, the universal nucleobase is inosine.
In additional embodiments, the endosymbiont parasite is selected from the group consisting of: Wolbachia endosymbiont of Dirofilaria immitis, Wolbachia endosymbiont of Onchocerca volvulus, Walbachia endosymbiont of W. bancrofti, Walbachia endosymbiont of B. timori, and Wolbachia endosymbiont of Brugia malayi. 
In some embodiments, the present invention provides compositions comprising an isolated primer 15-35 bases in length selected from the group consisting of SEQ ID NOs 1-10.
In particular embodiments, the present invention provides kits comprising at least one purified oligonucleotide primer pair that comprises forward and reverse primers that are about 20 to 35 nucleobases in length, and wherein the forward primer comprises at least 70% sequence identity with a sequence selected from the group consisting of SEQ ID NOS: 1, 3, 5, 7, and 9, and the reverse primer comprises at least 70% sequence identity with a sequence selected from the group consisting of SEQ ID NOS: 2, 4, 6, 8, and 10.
In certain embodiments, the present invention provides systems comprising: (a) a mass spectrometer configured to detect one or more molecular masses of amplicons produced using at least one purified oligonucleotide primer pair that comprises forward and reverse primers, wherein the primer pair comprises nucleic acid sequences that are substantially complementary to nucleic acid sequences from an endosymbiont; and (b) a controller operably connected to the mass spectrometer, the controller configured to correlate the molecular masses of the amplicons with one or more endosymbiont identities.
In further embodiments, the forward and reverse primers are about 15 to 35 nucleobases in length, and wherein the forward primer comprises at least 70% sequence identity with a sequence selected from the group consisting of SEQ ID NOS: 1, 3, 5, 7, and 9, and the reverse primer comprises at least 70% sequence identity with a sequence selected from the group consisting of SEQ ID NOS: 2, 4, 6, 8, and 10.
In other aspects, the invention provides methods of detecting a parasite associated with an endosymbiont. In some of these embodiments, the methods include detecting a presence of said endosymbiont in a sample, thereby detecting said parasite associated with said endosymbiont. In certain embodiments, said detecting comprises detecting nucleic acid from said endosymbiont using a nucleic acid detection assay.
In other aspects, the invention provides methods of detecting an endosymbiont associated with a parasite. In some of these embodiments, the methods include detecting a presence of said parasite in a sample, thereby detecting said endosymbiont associated with said parasite. In certain embodiments, said detecting comprises detecting nucleic acid from said parasite using a nucleic acid detection assay.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary and detailed description is better understood when read in conjunction with the accompanying drawings which are included by way of example and not by way of limitation.
FIG. 1 shows a process diagram illustrating one embodiment of an exemplary primer pair selection process.
FIG. 2 shows a process diagram illustrating one embodiment of the primer pair validation process. Here select primers are shown meeting test criteria. Criteria include but are not limited to, the ability to amplify targeted endosymbiont (e.g., Wolbachia species) nucleic acid, the ability to exclude non-target bioagents, the ability to not produce unexpected amplicons, the ability to not dimerize, the ability to have analytical limits of detection of ≦100 genomic copies/reaction, and the ability to differentiate amongst different target organisms.
FIG. 3 shows a process diagram illustrating an embodiment of an exemplary calibration method.
FIG. 4 shows a block diagram showing a representative system.
FIG. 5 shows the spectra of heartworm endosymbiont detection using primer pair BCT3569.
FIG. 6 shows the spectra of heartworm endosymbiont detection using primer pair BCT3575.
FIG. 7 shows the spectra of heartworm endosymbiont detection using primer pair BCT346.
FIG. 8 shows the spectra of heartworm endosymbiont detection using primer pair BCT348.
FIG. 9 shows the spectra of heartworm endosymbiont detection using primer pair BCT360.



DEFINITIONS
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. Further, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In describing and claiming the present invention, the following terminology and grammatical variants will be used in accordance with the definitions set forth below.
As used herein, the term “about” means encompassing plus or minus 10%. For example, about 200 nucleotides refers to a range encompassing between 180 and 220 nucleotides.
As used herein, the term “amplicon” or “bioagent identifying amplicon” refers to a nucleic acid generated using the primer pairs described herein. The amplicon is typically double stranded DNA; however, it may be RNA and/or DNA:RNA. In some embodiments, the amplicon comprises DNA complementary to endosymbiont RNA, DNA, or cDNA. In some embodiments, the amplicon comprises sequences of conserved regions/primer pairs and intervening variable region. As discussed herein, primer pairs are configured to generate amplicons from endosymbiont nucleic acid. As such, the base composition of any given amplicon may include the primer pair, the complement of the primer pair, the conserved regions and the variable region from the endosymbiont that was amplified to generate the amplicon. One skilled in the art understands that the incorporation of the designed primer pair sequences into an amplicon may replace the native sequences at the primer binding site, and complement thereof. In certain embodiments, after amplification of the target region using the primers the resultant amplicons having the primer sequences are used to generate the base composition data. Endosymbiont identifying amplicons generate base compositions that are preferably unique to the identity of an endosymbiont associated with a parasite.
The term “amplifying” or “amplification” in the context of nucleic acids refers to the production of multiple copies of a polynucleotide, or a portion of the polynucleotide, typically starting from a small amount of the polynucleotide (e.g., a single polynucleotide molecule), where the amplification products or amplicons are generally detectable. Amplification of polynucleotides encompasses a variety of chemical and enzymatic processes. The generation of multiple DNA copies from one or a few copies of a target or template DNA molecule during a polymerase chain reaction (PCR) or a ligase chain reaction (LCR) are forms of amplification. Amplification is not limited to the strict duplication of the starting molecule. For example, the generation of multiple cDNA molecules from a limited amount of RNA in a sample using reverse transcription (RT)-PCR is a form of amplification. Furthermore, the generation of multiple RNA molecules from a single DNA molecule during the process of transcription is also a form of amplification.
As used herein, the term “base composition” or “base count” refers to the number of each residue comprised in an amplicon or other nucleic acid, without consideration for the linear arrangement of these residues in the strand(s) of the amplicon. The amplicon residues comprise, adenosine (A), guanosine (G), cytidine, (C), (deoxy)thymidine (T), uracil (U), inosine (I), nitroindoles such as 5-nitroindole or 3-nitropyrrole, dP or dK (Hill F et al. Polymerase recognition of synthetic oligodeoxyribonucleotides incorporating degenerate pyrimidine and purine bases. Proc Natl Acad Sci USA. 1998 Apr. 14; 95(8):4258-63), an acyclic nucleoside analog containing 5-nitroindazole (Van Aerschot et al., Nucleosides and Nucleotides, 1995, 14, 1053-1056), the purine analog 1-(2-deoxy-beta-D-ribofuranosyl)-imidazole-4-carboxamide, 2,6-diaminopurine, 5-propynyluracil, 5-propynylcytosine, phenoxazines, including G-clamp, 5-propynyl deoxy-cytidine, deoxy-thymidine nucleotides, 5-propynylcytidine, 5-propynyluridine and mass tag modified versions thereof, including 7-deaza-2′-deoxyadenosine-5-triphosphate, 5-iodo-2′-deoxyuridine-5′-triphosphate, 5-bromo-2′-deoxyuridine-5′-triphosphate, 5-bromo-2′-deoxycytidine-5′-triphosphate, 5-iodo-2′-deoxycytidine-5′-triphosphate, 5-hydroxy-2′-deoxyuridine-5′-triphosphate, 4-thiothymidine-5′-triphosphate, 5-aza-2′-deoxyuridine-5′-triphosphate, 5-fluoro-2′-deoxyuridine-5′-triphosphate, O6-methyl-2′-deoxyguanosine-5′-triphosphate, N2-methyl-2′-deoxyguanosine-5′-triphosphate, 8-oxo-2′-deoxyguanosine-5′-triphosphate or thiothymidine-5′-triphosphate. In some embodiments, the mass-modified nucleobase comprises 15N or 13C or both 15N and 13C. In some embodiments, the non-natural nucleosides used herein include 5-propynyluracil, 5-propynylcytosine and inosine. Herein the base composition for an unmodified DNA amplicon is notated as AwGxCyTz, wherein w, x, y and z are each independently a whole number representing the number of said nucleoside residues in an amplicon. Base compositions for amplicons comprising modified nucleosides are similarly notated to indicate the number of said natural and modified nucleosides in an amplicon.
The term “partial base composition” or “partial base count” refers to the number of each residue of at least one nucleobase type (e.g., a given purine nucleobase type, a given pyrimidine nucleobase type, a given nucleobase analog type, and/or the like), but not each residue comprised in an amplicon or other nucleic acid (e.g., for single or multiple strands of those nucleic acids), without consideration for the linear arrangement of these residues in the strand(s) of the amplicon. For example, if a given amplicon or other nucleic acid includes four nucleobase types (e.g., adenosine (A), guanosine (G), cytidine, (C), and (deoxy)thymidine (T)), a partial base count for that amplicon or other nucleic acid would include the number of any one of those four nucleobase types (e.g., [Aw], [Gx], [Cy], or [Tz]), any two of those four nucleobase types (e.g., [AwGx], [AwCy], [AwTz], [GxCy], [GxTz], or [CyTz]), or at most any three of those four nucleobase types (e.g., [AwGxCy], [AwCyTz], [AwGxTz], or [GxCyTz]), in which w, x, y and z are each independently a whole number representing the number of said nucleoside residues in that amplicon or other nucleic acid. To further illustrate, if a nucleic acid has the following composition: ATTGCCTAAGGTTAACG (SEQ ID NO: 11), then partial base counts for that nucleic acid include [A5], [G4], [C3], [T5], [A5G4], [A5C3], [A5T5], [G4C3], [G4T5], [C3T5], [A5G4C3], [A5C3T5], [A5G4T5], or [G4C3T5].
As used herein, a “base composition probability cloud” is a representation of the diversity in base composition resulting from a variation in sequence that occurs among different isolates of a given species, family or genus. Base composition calculations for a plurality of amplicons are mapped on a pseudo four-dimensional plot. Related members in a family, genus or species typically cluster within this plot, forming a base composition probability cloud.
As used herein, the term “base composition signature” refers to the base composition generated by any one particular amplicon.
As used herein, a “bioagent” means any biological organism or component thereof or a sample containing a biological organism or component thereof, including microorganisms or infectious substances, or any naturally occurring, bioengineered or synthesized component of any such microorganism or infectious substance or any nucleic acid derived from any such microorganism or infectious substance. Those of ordinary skill in the art will understand fully what is meant by the term bioagent given the instant disclosure. Still, a non-exhaustive list of bioagents includes: cells, cell lines, human clinical samples, mammalian blood samples, cell cultures, bacterial cells, viruses, viroids, fungi, protists, parasites, rickettsiae, protozoa, animals, mammals or humans. Samples may be alive, non-replicating or dead or in a vegetative state (for example, vegetative bacteria or spores).
As used herein, a “bioagent division” is defined as group of bioagents above the species level and includes but is not limited to, orders, families, genus, classes, clades, genera or other such groupings of bioagents above the species level.
As used herein, “broad range survey primers” are primers designed to identify an unknown bioagent as a member of a particular biological division (e.g., an order, family, class, clade, or genus). However, in some cases the broad range survey primers are also able to identify unknown bioagents at the species or sub-species level. As used herein, “division-wide primers” are primers designed to identify a bioagent at the species level and “drill-down” primers are primers designed to identify a bioagent at the sub-species level. As used herein, the “sub-species” level of identification includes, but is not limited to, strains, subtypes, variants, and isolates. Drill-down primers are not always required for identification at the sub-species level because broad range survey intelligent primers may, in some cases provide sufficient identification resolution to accomplishing this identification objective. Broad range survey primers may be used in the non-mass determined base compositions methods and systems of the present invention.
As used herein, the terms “complementary” or “complementarity” are used in reference to polynucleotides (i.e., a sequence of nucleotides) related by the base-pairing rules. For example, the sequence “5′-A-G-T-3′,” is complementary to the sequence “3′-T-C-A-5′.” Complementarity may be “partial,” in which only some of the nucleic acids' bases are matched according to the base pairing rules. Or, there may be “complete” or “total” complementarity between the nucleic acids. The degree of complementarity between nucleic acid strands has significant effects on the efficiency and strength of hybridization between nucleic acid strands. This is of particular importance in amplification reactions, as well as detection methods that depend upon binding between nucleic acids.
The term “conserved region” in the context of nucleic acids refers to a nucleobase sequence (e.g., a subsequence of a nucleic acid, etc.) that is the same or similar in two or more different regions or segments of a given nucleic acid molecule (e.g., an intramolecular conserved region), or that is the same or similar in two or more different nucleic acid molecules (e.g., an intermolecular conserved region). To illustrate, a conserved region may be present in two or more different taxonomic ranks (e.g., two or more different genera, two or more different species, two or more different subspecies, and the like) or in two or more different nucleic acid molecules from the same organism. To further illustrate, in certain embodiments, nucleic acids comprising at least one conserved region typically have between about 70%-100%, between about 80-100%, between about 90-100%, between about 95-100%, or between about 99-100% sequence identity in that conserved region. A conserved region may also be selected or identified functionally as a region that permits generation of amplicons via primer extension through hybridization of a completely or partially complementary primer to the conserved region for each of the target sequences to which conserved region is conserved.
As used herein, in some embodiments the term “database” is used to refer to a collection of base composition and/or partial base composition data. The base composition data in the database is indexed to bioagents and to primer pairs. The base composition data reported in the database comprises the number of at least one type of nucleoside in an amplicon (e.g., A17) that would be generated for each bioagent using each primer. The database can be populated by empirical data. In this aspect of populating the database, a bioagent is selected and a primer pair is used to generate an amplicon. Note that base composition entries in the database may be derived from sequencing data (i.e., known sequence information) or mass spectrometry data. An entry in the database is made to associate correlate the base composition with the bioagent (e.g., endosymbiont) and the primer pair used. The database may also be populated using other databases comprising bioagent (e.g., endosymbiont) information. For example, using the GenBank database it is possible to perform electronic PCR using an electronic representation of a primer pair. This in silico method may provide the base composition for any or all selected bioagent(s) stored in the GenBank database. The information may then be used to populate the base composition database as described above. A base composition database can be in silico, a written table, a reference book, a spreadsheet or any form generally amenable to databases. Preferably, it is in silico on computer readable media.
The term “detect”, “detecting” or “detection” refers to an act of determining the existence or presence of one or more targets (e.g., bioagent nucleic acids, amplicons, etc.) in a sample.
As used herein, the term “etiology” refers to the causes or origins, of diseases or abnormal physiological conditions.
Nucleic acids are “extended” or “elongated” when additional nucleotides (or other analogous molecules) are incorporated into the nucleic acids. For example, a nucleic acid is optionally extended by a nucleotide incorporating biocatalyst, such as a polymerase that typically adds nucleotides at the 3′ terminal end of a nucleic acid.
An “extended primer nucleic acid” refers to a primer nucleic acid to which one or more additional nucleotides have been added or otherwise incorporated (e.g., covalently bonded to).
As used herein, the term “gene” refers to a nucleic acid (e.g., DNA) sequence that comprises coding sequences necessary for the production of a polypeptide, precursor, or RNA (e.g., rRNA, tRNA). The polypeptide can be encoded by a full length coding sequence or by any portion of the coding sequence so long as the desired activity or functional properties (e.g., enzymatic activity, ligand binding, signal transduction, immunogenicity, etc.) of the full-length sequence or fragment thereof are retained.
A “genotype” refers to all or part of the genetic constitution of a nucleic acid molecule, cell or subject, or group of nucleic acid molecules, cells or subjects. For example, a genotype includes the particular mutations and/or alleles (e.g., polymorphisms, such as single nucleotide polymorphisms (SNPs) or the like) present at a given locus or distributed in a genome.
As used herein, the term “heterologous gene” refers to a gene that is not in its natural environment. For example, a heterologous gene includes a gene from one species introduced into another species. A heterologous gene also includes a gene native to an organism that has been altered in some way (e.g., mutated, added in multiple copies, linked to non-native regulatory sequences, etc). Heterologous genes are distinguished from endogenous genes in that the heterologous gene sequences are typically joined to nucleic acid sequences that are not found naturally associated with the gene sequences in the chromosome or are associated with portions of the chromosome not found in nature (e.g., genes expressed in loci where the gene is not normally expressed).
The terms “homology,” “homologous” and “sequence identity” refer to a degree of identity. There may be partial homology or complete homology. A partially homologous sequence is one that is less than 100% identical to another sequence. Determination of sequence identity is described in the following example: a primer 20 nucleobases in length which is otherwise identical to another 20 nucleobase primer but having two non-identical residues has 18 of 20 identical residues (18/20=0.9 or 90% sequence identity). In another example, a primer 15 nucleobases in length having all residues identical to a 15 nucleobase segment of a primer 20 nucleobases in length would have 15/20=0.75 or 75% sequence identity with the 20 nucleobase primer. In context of the present invention, sequence identity is meant to be properly determined when the query sequence and the subject sequence are both described and aligned in the 5′ to 3′ direction. Sequence alignment algorithms such as BLAST, will return results in two different alignment orientations. In the Plus/Plus orientation, both the query sequence and the subject sequence are aligned in the 5′ to 3′ direction. On the other hand, in the Plus/Minus orientation, the query sequence is in the 5′ to 3′ direction while the subject sequence is in the 3′ to 5′ direction. It should be understood that with respect to the primers of the present invention, sequence identity is properly determined when the alignment is designated as Plus/Plus. Sequence identity may also encompass alternate or “modified” nucleobases that perform in a functionally similar manner to the regular nucleobases adenine, thymine, guanine and cytosine with respect to hybridization and primer extension in amplification reactions. In a non-limiting example, if the 5-propynyl pyrimidines propyne C and/or propyne T replace one or more C or T residues in one primer which is otherwise identical to another primer in sequence and length, the two primers will have 100% sequence identity with each other. In another non-limiting example, Inosine (I) may be used as a replacement for G or T and effectively hybridize to C, A or U (uracil). Thus, if inosine replaces one or more C, A or U residues in one primer which is otherwise identical to another primer in sequence and length, the two primers will have 100% sequence identity with each other. Other such modified or universal bases may exist which would perform in a functionally similar manner for hybridization and amplification reactions and will be understood to fall within this definition of sequence identity.
As used herein, “housekeeping gene” or “core viral gene” refers to a gene encoding a protein or RNA involved in basic functions required for survival and reproduction of a bioagent. Housekeeping genes include, but are not limited to, genes encoding RNA or proteins involved in translation, replication, recombination and repair, transcription, nucleotide metabolism, amino acid metabolism, lipid metabolism, energy generation, uptake, secretion and the like.
As used herein, the term “hybridization” or “hybridize” is used in reference to the pairing of complementary nucleic acids. Hybridization and the strength of hybridization (i.e., the strength of the association between the nucleic acids) is influenced by such factors as the degree of complementary between the nucleic acids, stringency of the conditions involved, the melting temperature (Tm) of the formed hybrid, and the G:C ratio within the nucleic acids. A single molecule that contains pairing of complementary nucleic acids within its structure is said to be “self-hybridized.” An extensive guide to nucleic hybridization may be found in Tijssen, Laboratory Techniques in Biochemistry and Molecular Biology-Hybridization with Nucleic Acid Probes, part I, chapter 2, “Overview of principles of hybridization and the strategy of nucleic acid probe assays,” Elsevier (1993), which is incorporated by reference.
A “label” refers to a moiety attached (covalently or non-covalently), or capable of being attached, to a molecule, which moiety provides or is capable of providing information about the molecule (e.g., descriptive, identifying, etc. information about the molecule). Exemplary labels include fluorescent labels, non-fluorescent labels, colorimetric labels, chemiluminescent labels, bioluminescent labels, radioactive labels, mass-modifying groups, antibodies, antigens, biotin, haptens, and enzymes (including, e.g., peroxidase, phosphatase, etc.).
The term “kit” is used in reference to a combination of articles that facilitate a process, method, assay, analysis or manipulation of a sample. Kits can contain instructions describing how to use the kit (e.g., instructions describing the methods of the invention), primer nucleic acids, nucleotide incorporating biocatalysts, labeled nucleotides, chemical reagents, as well as any other components.
A “linker” or “spacer” refers to a chemical moiety that covalently or non-covalently (e.g., ionically, etc.) attaches a compound or substituent group to, e.g., a solid support, another compound or group, or the like. For example, a linker optionally attaches a label (e.g., a fluorescent dye, a radioisotope, etc.) to a nucleotide or the like. Linkers are typically bifunctional chemical moieties and in certain embodiments, they comprise cleavable attachments, which can be cleaved by, e.g., heat, an enzyme, a chemical agent, electromagnetic radiation, etc. to release materials or compounds from, e.g., a solid support, another compound, etc. A careful choice of linker allows cleavage to be performed under appropriate conditions compatible with the stability of the compound and assay method. Generally a linker has no specific biological activity other than to, e.g., join chemical species together or to preserve some minimum distance or other spatial relationship between such species. However, the constituents of a linker may be selected to influence some property of the linked chemical species such as three-dimensional conformation, net charge, hydrophobicity, etc. Additional description of linker molecules is provided in, e.g., Lyttle et al. (1996) Nucleic Acids Res, 24(14):2793, Shchepino et al. (2001) Nucleosides, Nucleotides, & Nucleic Acids 20:369, Doronina et al (2001) Nucleosides, Nucleotides, & Nucleic Acids 20:1007, Trawick et al. (2001) Bioconjugate Chem. 12:900, Olejnik et al. (1998) Methods in Enzymology 291:135, Pljevaljcic et al. (2003) J. Am. Chem. Soc. 125(12):3486, Ward, et. al., U.S. Pat. No. 4,711,955, Stavrianopoulos, U.S. Pat. No. 4,707,352, and Stavrianopoulos, U.S. Pat. No. 4,707,440, which are each incorporated by reference.
A “mass modifying” group modifies the mass, typically measured in terms of molecular weight as daltons, of a molecule that comprises the group. For example, mass modifying groups that increase the discrimination between at least two nucleic acids with single base differences in size or sequence can be used to facilitate sequencing using, e.g., molecular weight determinations.
A “mixture” refers to a combination of two or more different components. A “reaction mixture” refers a mixture that comprises molecules that can participate in and/or facilitate a given reaction.
The term “molecular mass” refers to the mass of a compound (e.g., a nucleic acid, etc.) as determined, for example, using mass spectrometry.
A “modified” enzyme refers to an enzyme comprising a monomer sequence in which at least one monomer of the sequence differs from a monomer in a reference sequence, such as a native or wild-type form of the enzyme or another modified form of the enzyme, e.g., when the two sequences are aligned for maximum identity. Exemplary modifications include monomer insertions, deletions, and substitutions. The modified enzymes (i.e., protein- or nucleic acid-based catalysts) of the invention have been or are optionally created by various diversity generating methods. Although essentially any method can be used to produce a modified enzyme, certain exemplary techniques include recombining (e.g., via recursive recombination, synthetic recombination, or the like) two or more nucleic acids encoding one or more parental enzymes, or by mutating one or more nucleic acids that encode enzymes, e.g., using recursive ensemble mutagenesis, cassette mutagenesis, random mutagenesis, in vivo mutagenesis, site directed mutagenesis, or the like. A nucleic acid encoding a parental enzyme typically includes a gene that, through the mechanisms of transcription and translation, produces an amino acid sequence corresponding to a parental enzyme, e.g., a native form of the enzyme. Modified enzymes also include chimeric enzymes that have identifiable component sequences (e.g., structural and/or functional domains, etc.) derived from two or more parents. Also included within the definition of modified enzymes are those comprising chemical modifications (e.g., attached substituent groups, altered substituent groups, etc.) relative to a reference sequence.
A “moiety” or “group” refers to one of the portions into which something, such as a molecule, is divided (e.g., a functional group, substituent group, or the like). For example, a nucleotide typically comprises a basic group (e.g., adenine, thymine, cytosine, guanine, uracil, or an analog basic group), a sugar moiety (e.g., a moiety comprising a sugar ring or an analog thereof), and one or more phosphate groups.
As used herein, the term “primer” or “primer nucleic acid” refers to an oligonucleotide, whether occurring naturally as in a purified restriction digest or produced synthetically, that is capable of acting as a point of initiation of synthesis when placed under conditions in which synthesis of a primer extension product that is complementary to a nucleic acid strand is induced (e.g., in the presence of nucleotides and an inducing agent such as a biocatalyst (e.g., a DNA polymerase or the like) and at a suitable temperature and pH). The primer is typically single stranded for maximum efficiency in amplification, but may alternatively be double stranded. If double stranded, the primer is generally first treated to separate its strands before being used to prepare extension products. In some embodiments, the primer is an oligodeoxyribonucleotide. The primer is sufficiently long to prime the synthesis of extension products in the presence of the inducing agent. The exact lengths of the primers will depend on many factors, including temperature, source of primer and the use of the method.
As used herein, “intelligent primers” or “primers” or “primer pairs,” in some embodiments, are oligonucleotides that are designed to bind to conserved sequence regions of one or more bioagent (e.g., endosymbiont) nucleic acids to generate bioagent (e.g., endosymbiont) identifying amplicons. In some embodiments, the bound primers flank an intervening variable region between the conserved binding sequences. Upon amplification, the primer pairs yield amplicons e.g., amplification products that provide base composition variability between the two or more bioagents. The variability of the base compositions allows for the identification of one or more individual bioagents from, e.g., two or more bioagents based on the base composition distinctions. In some embodiments, the primer pairs are also configured to generate amplicons amenable to molecular mass analysis. Further, the sequences of the primer members of the primer pairs are not necessarily fully complementary to the conserved region of the reference bioagent. For example, in some embodiments, the sequences are designed to be “best fit” amongst a plurality of bioagents at these conserved binding sequences. Therefore, the primer members of the primer pairs have substantial complementarity with the conserved regions of the bioagents, including the reference bioagent.
In some embodiments of the invention, the oligonucleotide primer pairs described herein can be purified. As used herein, “purified oligonucleotide primer pair,” “purified primer pair,” or “purified” means an oligonucleotide primer pair that is chemically-synthesized to have a specific sequence and a specific number of linked nucleosides. This term is meant to explicitly exclude nucleotides that are generated at random to yield a mixture of several compounds of the same length each with randomly generated sequence. As used herein, the term “purified” or “to purify” refers to the removal of one or more components (e.g., contaminants) from a sample.
The term “nucleic acid” or “nucleic acid molecule” refers to any nucleic acid containing molecule, including but not limited to, DNA or RNA. The term encompasses sequences that include any of the known base analogs of DNA and RNA including, but not limited to, 4-acetylcytosine, 8-hydroxy-N6-methyladenosine, aziridinylcytosine, pseudoisocytosine, 5-(carboxyhydroxyl-methyl)-uracil, 5-fluorouracil, 5-bromouracil, 5-carboxymethylaminomethyl-2-thiouracil, 5-carboxymethyl-aminomethyluracil, dihydrouracil, inosine, N6-isopentenyladenine, 1-methyladenine, 1-methylpseudo-uracil, 1-methylguanine, 1-methylinosine, 2,2-dimethyl-guanine, 2-methyladenine, 2-methylguanine, 3-methyl-cytosine, 5-methylcytosine, N6-methyladenine, 7-methylguanine, 5-methylaminomethyluracil, 5-methoxy-amino-methyl-2-thiouracil, beta-D-mannosylqueosine, 5′-methoxycarbonylmethyluracil, 5-methoxyuracil, 2-methylthio-N-isopentenyladenine, uracil-5-oxyacetic acid methylester, uracil-5-oxyacetic acid, oxybutoxosine, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, N-uracil-5-oxyacetic acid methylester, uracil-5-oxyacetic acid, pseudouracil, queosine, 2-thiocytosine, and 2,6-diaminopurine.
As used herein, the term “nucleobase” is synonymous with other terms in use in the art including “nucleotide,” “deoxynucleotide,” “nucleotide residue,” “deoxynucleotide residue,” “nucleotide triphosphate (NTP),” or deoxynucleotide triphosphate (dNTP). As is used herein, a nucleobase includes natural and modified residues, as described herein.
A “nucleoside” refers to a nucleic acid component that comprises a base or basic group (e.g., comprising at least one homocyclic ring, at least one heterocyclic ring, at least one aryl group, and/or the like) covalently linked to a sugar moiety (e.g., a ribose sugar, etc.), a derivative of a sugar moiety, or a functional equivalent of a sugar moiety (e.g., an analog, such as carbocyclic ring). For example, when a nucleoside includes a sugar moiety, the base is typically linked to a 1′-position of that sugar moiety. As described above, a base can be naturally occurring (e.g., a purine base, such as adenine (A) or guanine (G), a pyrimidine base, such as thymine (T), cytosine (C), or uracil (U)), or non-naturally occurring (e.g., a 7-deazapurine base, a pyrazolo[3,4-d]pyrimidine base, a propynyl-dN base, etc.). Exemplary nucleosides include ribonucleosides, deoxyribonucleosides, dideoxyribonucleosides, carbocyclic nucleosides, etc.).
A “nucleotide” refers to an ester of a nucleoside, e.g., a phosphate ester of a nucleoside. For example, a nucleotide can include 1, 2, 3, or more phosphate groups covalently linked to a 5′ position of a sugar moiety of the nucleoside.
A “nucleotide incorporating biocatalyst” refers to a catalyst that catalyzes the incorporation of nucleotides into a nucleic acid. Nucleotide incorporating biocatalysts are typically enzymes. An “enzyme” is a protein- and/or nucleic acid-based catalyst that acts to reduce the activation energy of a chemical reaction involving other compounds or “substrates.” A “nucleotide incorporating enzyme” refers to an enzyme that catalyzes the incorporation of nucleotides into a nucleic acid. Exemplary nucleotide incorporating enzymes include, e.g., DNA polymerases, RNA polymerases, terminal transferases, reverse transcriptases, telomerases, polynucleotide phosphorylases, and the like.
An “oligonucleotide” refers to a nucleic acid that includes at least two nucleic acid monomer units (e.g., nucleotides), typically more than three monomer units, and more typically greater than ten monomer units. The exact size of an oligonucleotide generally depends on various factors, including the ultimate function or use of the oligonucleotide. To further illustrate, oligonucleotides are typically less than 200 residues long (e.g., between 15 and 100), however, as used herein, the term is also intended to encompass longer polynucleotide chains. Oligonucleotides are often referred to by their length. For example a 24 residue oligonucleotide is referred to as a “24-mer”. Typically, the nucleoside monomers are linked by phosphodiester bonds or analogs thereof, including phosphorothioate, phosphorodithioate, phosphoroselenoate, phosphorodiselenoate, phosphoroanilothioate, phosphoranilidate, phosphoramidate, and the like, including associated counterions, e.g., H+, NH4+, Na+, and the like, if such counterions are present. Further, oligonucleotides are typically single-stranded. Oligonucleotides are optionally prepared by any suitable method, including, but not limited to, isolation of an existing or natural sequence, DNA replication or amplification, reverse transcription, cloning and restriction digestion of appropriate sequences, or direct chemical synthesis by a method such as the phosphotriester method of Narang et al. (1979) Meth Enzymol. 68: 90-99; the phosphodiester method of Brown et al. (1979) Meth Enzymol. 68: 109-151; the diethylphosphoramidite method of Beaucage et al. (1981) Tetrahedron Lett. 22: 1859-1862; the triester method of Matteucci et al. (1981) J Am Chem Soc. 103:3185-3191; automated synthesis methods; or the solid support method of U.S. Pat. No. 4,458,066, entitled “PROCESS FOR PREPARING POLYNUCLEOTIDES,” issued Jul. 3, 1984 to Caruthers et al., or other methods known to those skilled in the art. All of these references are incorporated by reference.
As used herein a “sample” refers to anything capable of being analyzed by the methods provided herein. In some embodiments, the sample comprises or is suspected to comprise one or more nucleic acids capable of analysis by the methods. Preferably, the samples comprise nucleic acids (e.g., DNA, RNA, cDNAs, etc.) from one or more bioagents. Samples can include, for example, blood, saliva, urine, feces, anorectal swabs, vaginal swabs, cervical swabs, and the like. In some embodiments, the samples are “mixture” samples, which comprise nucleic acids from more than one subject or individual. In some embodiments, the methods provided herein comprise purifying the sample or purifying the nucleic acid(s) from the sample. In some embodiments, the sample is purified nucleic acid.
A “sequence” of a biopolymer refers to the order and identity of monomer units (e.g., nucleotides, etc.) in the biopolymer. The sequence (e.g., base sequence) of a nucleic acid is typically read in the 5′ to 3′ direction.
As is used herein, the term “single primer pair identification” means that one or more bioagents can be identified using a single primer pair. A base composition signature for an amplicon may singly identify one or more bioagents.
A “solid support” refers to a solid material which can be derivatized with, or otherwise attached to, a chemical moiety, such as a primer nucleic acid, a template nucleic acid, or the like. Exemplary solid supports include a zero-mode waveguide array, a plate, a bead, a microbead, a fiber, a whisker, a comb, a hybridization chip, a membrane, a single crystal, a ceramic layer, a self-assembling monolayer, and the like.
As used herein, a “sub-species characteristic” is a genetic characteristic that provides the means to distinguish two members of the same bioagent (e.g., endosymbiont) species. For example, one Wolbachia strain may be distinguished from another viral strain of the same species by possessing a genetic change (e.g., for example, a nucleotide deletion, addition or substitution) in one of the Wolbachia genes.
A “subsequence” or “fragment” refers to any portion of an entire nucleic acid sequence.
As used herein, in some embodiments the term “substantial complementarity” means that a primer member of a primer pair comprises between about 70%-100%, or between about 80-100%, or between about 90-100%, or between about 95-100%, or between about 99-100% complementarity with the conserved binding sequence of a nucleic acid from a given bioagent. These ranges of complementarity and identity are inclusive of all whole or partial numbers embraced within the recited range numbers. For example, and not limitation, 75.667%, 82%, 91.2435% and 97% complementarity or sequence identity are all numbers that fall within the above recited range of 70% to 100%, therefore forming a part of this description.
A “system” in the context of analytical instrumentation refers a group of objects and/or devices that fonn a network for performing a desired objective.
A “template nucleic acid” refers to a nucleic acid to which a primer nucleic acid can hybridize and be extended. Accordingly, template nucleic acids include subsequences that are at least partially complementary to the primer nucleic acids. Template nucleic acids can be derived from essentially any source (preferably endosymbionts of parasites). To illustrate, template nucleic acids are optionally derived or isolated from, e.g., cultured microorganisms, uncultured microorganisms, complex biological mixtures, tissues, sera, pooled sera or tissues, multispecies consortia, ancient, fossilized or other nonliving biological remains, environmental isolates, soils, groundwaters, waste facilities, deep-sea environments, or the like. Further, template nucleic acids optionally include or are derived from, e.g., individual cDNA molecules, cloned sets of cDNAs, cDNA libraries, extracted RNAs, natural RNAs, in vitro transcribed RNAs, characterized or uncharacterized genomic DNAs, cloned genomic DNAs, genomic DNA libraries, enzymatically fragmented DNAs or RNAs, chemically fragmented DNAs or RNAs, physically fragmented DNAs or RNAs, or the like. Template nucleic acids can also be chemically synthesized using techniques known in the art. In addition, template nucleic acids optionally correspond to at least a portion of a gene or are complementary thereto.
As used herein, “triangulation identification” means the use of more than one primer pair to generate a corresponding amplicon for identification of a bioagent (e.g, endosymbiont). The more than one primer pair can be used in individual wells or vessels or in a multiplex PCR assay. Alternatively, PCR reactions may be carried out in single wells or vessels comprising a different primer pair in each well or vessel. Following amplification the amplicons are pooled into a single well or container which is then subjected to base composition analysis (e.g., which does not involve molecular mass analysis). The combination of pooled amplicons can be chosen such that the expected ranges of base compositions of individual amplicons are not overlapping and thus will not complicate identification of signals. Triangulation is a process of elimination, wherein a first primer pair identifies that an unknown bioagent may be one of a group of bioagents. Subsequent primer pairs are used in triangulation identification to further refine the identity of the bioagent amongst the subset of possibilities generated with the earlier primer pair. Triangulation identification is complete when the identity of the bioagent is determined. The triangulation identification process may also be used to reduce false negative and false positive signals, and enable reconstruction of the origin of hybrid or otherwise engineered bioagents. For example, identification of the three part toxin genes typical of B. anthracis (Bowen et al., J Appl Microbiol., 1999, 87, 270-278) in the absence of the expected compositions from the B. anthracis genome would suggest a genetic engineering event.
As used herein, the term “unknown bioagent” can mean, for example: (i) a bioagent whose existence is not known (for example, the SARS coronavirus was unknown prior to April 2003) and/or (ii) a bioagent whose existence is known (such as the well known bacterial species Staphylococcus aureus for example) but which is not known to be in a sample to be analyzed. For example, if the method for identification of corona viruses disclosed in commonly owned U.S. patent Ser. No. 10/829,826 (incorporated herein by reference in its entirety) was to be employed prior to April 2003 to identify the SARS coronavirus in a clinical sample, both meanings of “unknown” bioagent are applicable since the SARS coronavirus was unknown to science prior to April, 2003 and since it was not known what bioagent (in this case a coronavirus) was present in the sample. On the other hand, if the method of U.S. patent Ser. No. 10/829,826 was to be employed subsequent to April 2003 to identify the SARS coronavirus in a clinical sample, the second meaning (ii) of “unknown” bioagent would apply because the SARS coronavirus became known to science subsequent to April 2003 because it was not known what bioagent was present in the sample.
As used herein, the term “variable region” is used to describe a region that falls between any one primer pair described herein. The region possesses distinct base compositions between at least two bioagents (e.g., two endosymbionts such as Wolbachia), such that at least one bioagent can be identified at, for example, the family, genus, species or sub-species level. The degree of variability between the at least two bioagents need only be sufficient to allow for identification using mass spectrometry analysis, as described herein.
As used herein, a “wobble base” is a variation in a codon found at the third nucleotide position of a DNA triplet. Variations in conserved regions of sequence are often found at the third nucleotide position due to redundancy in the amino acid code.
In certain embodiments, provided herein are methods, compositions, kits, and related systems for the detection and identification of bioagents (e.g., species of endosymbiont) using bioagent identifying amplicons. In some embodiments, primers are selected to hybridize to conserved sequence regions of nucleic acids derived from a bioagent and which flank variable sequence regions to yield a bioagent identifying amplicon which can be amplified and which is amenable to base composition analysis. In some embodiments, the corresponding base composition of one or more different amplicons is queried against a database of base compositions indexed to bioagents and to the primer pair used to generate the amplicon. A match of the measured base composition to a database entry base composition associates the sample bioagent to an indexed bioagent in the database. Thus, the identity of the unknown bioagent is determined. No prior knowledge of the unknown bioagent is necessary to make an identification. In some instances, the measured base composition associates with more than one database entry base composition. Thus, a second/subsequent primer pair is generally used to generate an amplicon, and its measured base composition is similarly compared to the database to determine its identity in triangulation identification. Furthermore, the methods and other aspects of the invention can be applied to rapid parallel multiplex analyses, the results of which can be employed in a triangulation identification strategy. Thus, in some embodiments, the present invention provides rapid throughput and does not require nucleic acid sequencing or knowledge of the linear sequences of nucleobases of the amplified target sequence for bioagent detection and identification.
DESCRIPTION OF THE INVENTION
The present invention provides systems, methods, and compositions for identifying a subject or a sample as infected with a parasite by detecting a biomolecule (e.g., nucleic acid) from an endosymbiont of the parasite in a sample (e.g., from the subject). In certain embodiments, the parasite is a nematode that infects humans or dogs (e.g., D. immitis, O. volvulus, W. bancrofti, B. timori, or B. malayi) and the endosymbiont is Wolbachia. In particular embodiments, detection of the endosymbiont employs at least one primer pair specific for the endosymbiont.
One advantage of exemplary methods of the present invention is that a parasite can be detected in a subject (e.g., dog, human, etc.) without the need for a biopsy of any type. Instead, a sample, such as a blood sample, stool sample, or urine sample can be tested for the presence of endosymbiont bacteria that serve as a proxy for the presence of the parasite (e.g., such a long worm). Another advantage of certain methods of the present invention is that it provides a quick detection of a parasite (e.g., heartworm or other nematode) directly from samples by PCR. In some embodiments, such as those employing PCR or other amplification, such assays can be incorporated into a diagnostic panel quickly and easily. Detection of parasites (e.g., heartworm) by detection of its endosymbiont has another advantage it that there may be many endosymbiont genome copies per parasite genome.
A. Parasites and Endosymbionts
The present invention is not limited by the type of parasite that is detected by presence of an associated endosymbiont. The present invention is also not limited by the type of endosymbiont that is detected, so long as it is known to be associated with a particular parasite desired to be detected.
In certain embodiments, the parasite detected is selected from Dirofilaria immitis, Onchocerca volvulus, Wuchereria bancrofti, Brugia timori, and Brugia malayi. In particular embodiments, Wolbachia species associated with these parasites are detected. Nucleic acid sequences for these particular Wolbachia species are as follows and can be used to design primers for amplification or for designing other detection assays.
The following are Genbank accession numbers and GI numbers for genomic sequences from the Wolbachia endosymbiont of Onchocerca volvulus: FJ390367.1 (GI:213401069), FJ390355.1 (GI:213401045), FJ390343.1 (GI:213401021), FJ390332.1 (GI:213400999), FJ390326.1 (GI:213400987), FJ390297.1 (GI:213400929), FJ390283.1 (GI:213400900), FJ390270.1 (GI:213400874), FJ390258.1 (GI:213400850), FJ390245.1 (GI:213400824), FJ390229.1 (GI:213400792), FJ390183.1 (GI:213400700), FJ390159.1 (GI:213400652), FJ390148.1 (GI:213400630), CU062464.1 (GI:111073624), CU062463.1 (GI:111073615), CU062461.1 (GI:111073604), CU062460.1 (GI:111073591), AF069069.1 (GI:3212091), AY255127.1 (GI:32330660), AF412405.1 (GI:18141013), AF282845.1 (GI:10644665), AF069070.1 (GI:3212092), HB940658.1 (GI:259678960), HB925003.1 (GI:259676894), HB938880.1 (GI:259672080), HB953865.1 (GI:259671028), HB952496.1 (GI:259667295), HB937229.1 (GI:259666333), HB917834.1 (GI:259455898), HB896148.1 (GI:259455199), HB903443.1 (GI:259439933), HB900933.1 (GI:259421957), GN100713.1 (GI:227287020), FJ390217.1 (GI:213400768), AM403096.1 (GI:157677000), CU062443.1 (GI:111035795), X82176.1 (GI:558624), AJ303385.1 (GI:18129326), AJ276501.1 (GI:9857237), and AJ276496.1 (GI:9857230).
Genbank accession number AE017321.1 and GI number GI:58418577 corresponds to the complete genomic sequence of Wolbachia endosymbiont of Brugia malayi. 
The following are Genbank accession numbers and GI numbers for genomic sequences from the Wolbachia endosymbiont of dirofilaria immitis: ET041565.1 (GI:158132514), ET041564.1 (GI:158132513), ET041563.1 (GI:158132512), ET041562.1 (GI:158132511), ET041561.1 (GI:158132510), ET041560.1 (GI:158132509), ET041559.1 (GI:158132508), ET041585.1 (GI:158132534), ET041584.1 (GI:158132533), ET041583.1 (GI:158132532), ET041582.1 (GI:158132531), ET041581.1 (GI:158132530), ET041580.1 (GI:158132529), ET041579.1 (GI:158132528), ET041578.1 (GI:158132527), ET041577.1 (GI:158132526), ET041576.1 (GI:158132525), ET041575.1 (GI:158132524), ET041574.1 (GI:158132523), ET041573.1 (GI:158132522), ET041572.1 (GI:158132521), ET041571.1 (GI:158132520), ET041570.1 (GI:158132519), ET041569.1 (GI:158132518), ET041568.1 (GI:158132517), ET041567.1 (GI:158132516), ET041566.1 (GI:158132515), ET041605.1 (GI:158132554), ET041604.1 (GI:158132553), ET041603.1 (GI:158132552), ET041602.1 (GI:158132551), ET041601.1 (GI:158132550), ET041600.1 (GI:158132549), ET041599.1 (GI:158132548), ET041598.1 (GI:158132547), ET041597.1 (GI:158132546), ET041596.1 (GI:158132545), ET041595.1 (GI:158132544), ET041594.1 (GI:158132543), ET041593.1 (GI:158132542), ET041592.1 (GI:158132541), ET041591.1 (GI:158132540), ET041590.1 (GI:158132539), ET041589.1 (GI:158132538), ET041588.1 (GI:158132537), ET041587.1 (GI:158132536), ET041586.1 (GI:158132535), ET041625.1 (GI:158132574), ET041624.1 (GI:158132573), ET041623.1 (GI:158132572), ET041622.1 (GI:158132571), ET041621.1 (GI:158132570), ET041620.1 (GI:158132569), ET041619.1 (GI:158132568), ET041618.1 (GI:158132567), ET041617.1 (GI:158132566), ET041616.1 (GI:158132565), ET041615.1 (GI:158132564), ET041614.1 (GI:158132563), ET041613.1 (GI:158132562), ET041612.1 (GI:158132561), ET041611.1 (GI:158132560), ET041610.1 (GI:158132559), ET041609.1 (GI:158132558), ET041608.1 (GI:158132557), ET041607.1 (GI:158132556), ET041606.1 (GI:158132555), ET041645.1 (GI:158132594), ET041644.1 (GI:158132593), ET041643.1 (GI:158132592), ET041642.1 (GI:158132591), ET041641.1 (GI:158132590), ET041640.1 (GI:158132589), ET041639.1 (GI:158132588), ET041638.1 (GI:158132587), ET041637.1 (GI:158132586), ET041636.1 (GI:158132585), ET041635.1 (GI:158132584), ET041634.1 (GI:158132583), ET041633.1 (GI:158132582), ET041632.1 (GI:158132581), ET041631.1 (GI:158132580), ET041630.1 (GI:158132579), ET041629.1 (GI:158132578), ET041628.1 (GI:158132577), ET041627.1 (GI:158132576), ET041626.1 (GI:158132575), ET041665.1 (GI:158132614), ET041664.1 (GI:158132613), ET041663.1 (GI:158132612), ET041662.1 (GI:158132611), ET041661.1 (GI:158132610), ET041660.1 (GI:158132609), ET041659.1 (GI:158132608), ET041658.1 (GI:158132607), ET041657.1 (GI:158132606), ET041656.1 (GI:158132605), ET041655.1 (GI:158132604), ET041654.1 (GI:158132603), ET041653.1 (GI:158132602), ET041652.1 (GI:158132601), ET041651.1 (GI:158132600), ET041650.1 (GI:158132599), ET041649.1 (GI:158132598), ET041648.1 (GI:158132597), ET041647.1 (GI:158132596), and ET041646.1 (GI:158132595).
The following are Genbank accession numbers and (GI numbers for genomic sequences from the Wolbachia endosymbiont of Wuchereria bancrofti: GU196272.1 (GI:272472262), GU196271.1 (GI:272472260), GU196270.1 (GI:272472258), AF285273.1 (GI:12231861), AF081198.1 (GI:3493124), AJ303389.1 (GI:18129334), AJ252180.1 (GI:8894898), AF093510.1 (GI:6002626), AF285274.1 (GI:12231863), DQ093835.1 (GI:70610294), DQ093834.1 (GI:70610292), DQ093833.1 (GI:70610290), DQ093832.1 (GI:70610288), DQ093831.1 (GI:70610286), DQ093830.1 (GI:70610284), DQ093850.1 (GI:70610282), DQ093849.1 (GI:70610280), DQ093848.1 (GI:70610278), DQ093847.1 (GI:70610276), and DQ093846.1 (GI:70610274).
The following are Genbank accession numbers and (GI numbers for genomic sequences from the Wolbachia endosymbiont of Brugia timori: AF499134.1 (GI:21667643) and AF499135.1 (GI:21667644).
In certain embodiments, the parasite detected is a nematode known to infect humans. Examples of such parasites are described in Table 1.









TABLE 1





Common name of organism




or disease
Latin name
Body part affected







Whipworm
Trichuris michiura, Trichuris vulpis
large intestine, anus


urinary schistosomiasis
Schistosoma haematobium
kidney, bladder, ureters, lungs, skin


Trichinosis
Trichinella spiralis, Trichinella britovi. Trichinella nelsoni,
muscle, periorbital region, small



Trichinella nativa
intestine


Toxocariasis
Toxocara canis, Toxocara can
liver, brain, eyes (Toxocara canis -




Visceral larva migrans. Ocular larva




migrans)


Tapeworm - Tapeworm infection
Cestoda
intestine


Swimmer's itch
Trichobilharzia rogenii, Schistosomatidae



Stroangyloidiasis - Parasitic pneumonia
Strongyloides stercoralis
Intestines, lungs, skin (Larva currens)


Sparganosis
Sptrometra erinacereuropael



Schistosomiasis by Schistosoma
Schistosoma japonicum
intestine, liver, spleen, lungs, skin


japonicum




Schistosomiasis - bilharzia, bilharziosis
Schistosoma sp.



or snail fever (all types)




Roundworm - Parasitic pneumonia
Ascaris sp. Ascaris lumbricoides
Intestines, liver, appendix, pancreas,




lungs, Loffler's syndrome


Roundworm
Baylisascaris Baylisascaris procyonis, Baylisascaris melts,




Baylisascaris transfuga. Baylisascaris columnaris, Baylisascaris




davosi, Baylisascaris laevis



River blindness
Onchocerca volvulus. Onchocerciasis
skin, eye, tissue


Pork tapeworm
Taenia solium



Pinworm - Enterobiasis
Enterobius vermicularis. Enterobius gregorii
intestines, anus


Paragonimiasis, Lung Fluke
Paragonimus westermant; Paragonimus africanus; Paragonimus
lungs



caliensis; Paragonimus kellicorri: Paragonimus skrjabini;




Paragonimus uterobilateralis



Metagonimiasis - intestinal fluke
Metagonimus yokogawai



Mansonelliasis, Filariasis
Mansonella streprocerca
subcutaneous layer of skin


Loa loa filariasis, Calabar swellings
Loa loa filaria
Connective tissue, lungs, eye


Liver fluke - Fasciolosis[4]
Fasciola hepatica, Fasciola gigantica
liver, gall blader


intestinal schistosomiasis
Schistosoma monsoni
intestine, liver, spleen, lungs, skin


Hymenolepiasis[7]
Hymenolepis nana. Hymenolepis diminuia



Guinea worm - Dracunculiasis
Dracunculus modinensis
subcutaneous tissues, muscle


Gnathostomiasis[6]
Gnathostoma spinigerum, Gnathostoma hispidum
subcutaneous tissues (under the skin)


Fasciolopsiasis - intestinal fluke[5]
Fasciolopsis buski
intestines


ElephantiasisLymphatic filariasis
Wuchereria bancrofti
lymphatic system


Echinococcosis - tapeworm
Echinococcus granulosus, Echinococcus multilocularis, E. vogeli,




E. oligarthrus
liver, lungs, kidney, spleen


Diphyllobothriasis - tapeworm
Diphyllobothrium latum
intestines, blood


Dioctophyme renalis infection
Dioctophyme renale
kidneys (typically the right)


Clonorchiasis
Clonorchis sinensis: Clonorchis viverrini



Chinese Liver Fluke
Opisthorchis viverrini, Opisthorchis felinenus, Clonorchis sinensis
bile duct


Beef tapeworm
Taenia saginata
Intestines


Asian intestinal schistosomiasis
Schistosoma mekongi - 



Anisakiasis[3]
Anisakis
allergic reaction


Ancylostomiasis/Hookworm
Ancylostomo duodenalo, Necator americanus
lungs, small intestine, blood



Brugia malayl, Brugia timori
lymph nodes



Dicrocoelium dendriicum
gall bladder



Echinostoma cchinarum
small intestine









B. Nucleic Acid Detection Assays
The present invention is not limited by the type of nucleic acid detection assay employed to detect endosymbiont nucleic acid. Any suitable assay may be employed. Exemplary detection methodologies are described below.
Endosymbiont nucleic acid may be detected by techniques that employ amplification prior to or simultaneous with detection. Illustrative non-limiting examples of nucleic acid amplification techniques include, but are not limited to, polymerase chain reaction (PCR), reverse transcription polymerase chain reaction (RT-PCR), transcription-mediated amplification (TMA), ligase chain reaction (LCR), strand displacement amplification (SDA), and nucleic acid sequence based amplification (NASBA). Those of ordinary skill in the art will recognize that certain amplification techniques (e.g., PCR) require that RNA be reversed transcribed to DNA prior to amplification (e.g., RT-PCR), whereas other amplification techniques directly amplify RNA (e.g., TMA and NASBA).
The polymerase chain reaction (U.S. Pat. Nos. 4,683,195, 4,683,202, 4,800,159 and 4,965,188, each of which is herein incorporated by reference in its entirety), commonly referred to as PCR, uses multiple cycles of denaturation, annealing of primer pairs to opposite strands, and primer extension to exponentially increase copy numbers of a target nucleic acid sequence. In a variation called RT-PCR, reverse transcriptase (RT) is used to make a complementary DNA (cDNA) from mRNA, and the cDNA is then amplified by PCR to produce multiple copies of DNA. For other various permutations of PCR see, e.g., U.S. Pat. Nos. 4,683,195, 4,683,202 and 4,800,159; Mullis et al., Meth. Enzymol. 155: 335 (1987); and, Murakawa et al., DNA 7: 287 (1988), each of which is herein incorporated by reference in its entirety.
Transcription mediated amplification (U.S. Pat. Nos. 5,480,784 and 5,399,491, each of which is herein incorporated by reference in its entirety), commonly referred to as TMA, synthesizes multiple copies of a target nucleic acid sequence autocatalytically under conditions of substantially constant temperature, ionic strength, and pH in which multiple RNA copies of the target sequence autocatalytically generate additional copies. See, e.g., U.S. Pat. Nos. 5,399,491 and 5,824,518, each of which is herein incorporated by reference in its entirety. In a variation described in U.S. Publ. No. 20060046265 (herein incorporated by reference in its entirety), TMA optionally incorporates the use of blocking moieties, terminating moieties, and other modifying moieties to improve TMA process sensitivity and accuracy.
The ligase chain reaction (Weiss, R., Science 254: 1292 (1991), herein incorporated by reference in its entirety), commonly referred to as LCR, uses two sets of complementary DNA oligonucleotides that hybridize to adjacent regions of the target nucleic acid. The DNA oligonucleotides are covalently linked by a DNA ligase in repeated cycles of thermal denaturation, hybridization and ligation to produce a detectable double-stranded ligated oligonucleotide product.
Strand displacement amplification (Walker, G. et al., Proc. Natl. Acad. Sci. USA 89: 392-396 (1992); U.S. Pat. Nos. 5,270,184 and 5,455,166, each of which is herein incorporated by reference in its entirety), commonly referred to as SDA, uses cycles of annealing pairs of primer sequences to opposite strands of a target sequence, primer extension in the presence of a dNTPαS to produce a duplex hemiphosphorothioated primer extension product, endonuclease-mediated nicking of a hemimodified restriction endonuclease recognition site, and polymerase-mediated primer extension from the 3′ end of the nick to displace an existing strand and produce a strand for the next round of primer annealing, nicking and strand displacement, resulting in geometric amplification of product. Thermophilic SDA (tSDA) uses thermophilic endonucleases and polymerases at higher temperatures in essentially the same method (EP Pat. No. 0 684 315).
Other amplification methods include, for example: nucleic acid sequence based amplification (U.S. Pat. No. 5,130,238, herein incorporated by reference in its entirety), commonly referred to as NASBA; one that uses an RNA replicase to amplify the probe molecule itself (Lizardi et al., BioTechnol. 6: 1197 (1988), herein incorporated by reference in its entirety), commonly referred to as Qβ replicase; a transcription based amplification method (Kwoh et al., Proc. Natl. Acad. Sci. USA 86:1173 (1989)); and, self-sustained sequence replication (Guatelli et al., Proc. Natl. Acad. Sci. USA 87: 1874 (1990), each of which is herein incorporated by reference in its entirety). For further discussion of known amplification methods see Persing, David H., “In Vitro Nucleic Acid Amplification Techniques” in Diagnostic Medical Microbiology: Principles and Applications (Persing et al., Eds.), pp. 51-87 (American Society for Microbiology, Washington, D.C. (1993)).
Another illustrative detection method provides for quantitative evaluation, of the amplification process in real-time. Evaluation of an amplification process in “real-time” involves determining the amount of amplicon in the reaction mixture either continuously or periodically during the amplification reaction, and using the determined values to calculate the amount of target sequence initially present in the sample. A variety of methods for determining the amount of initial target sequence present in a sample based on real-time amplification are well known in the art. These include methods disclosed in U.S. Pat. Nos. 6,303,305 and 6,541,205, each of which is herein incorporated by reference in its entirety. Another method for determining the quantity of target sequence initially present in a sample, but which is not based on a real-time amplification, is disclosed in U.S. Pat. No. 5,710,029, herein incorporated by reference in its entirety.
Amplification products may be detected in real-time through the use of various self-hybridizing probes, most of which have a stem-loop structure. Such self-hybridizing probes are labeled so that they emit differently detectable signals, depending on whether the probes are in a self-hybridized state or an altered state through hybridization to a target sequence. By way of non-limiting example, “molecular torches” are a type of self-hybridizing probe that includes distinct regions of self-complementarity (referred to as “the target binding domain” and “the target closing domain”) which are connected by a joining region (e.g., non-nucleotide linker) and which hybridize to each other under predetermined hybridization assay conditions. In a preferred embodiment, molecular torches contain single-stranded base regions in the target binding domain that are from 1 to about 20 bases in length and are accessible for hybridization to a target sequence present in an amplification reaction under strand displacement conditions. Under strand displacement conditions, hybridization of the two complementary regions, which may be fully or partially complementary, of the molecular torch is favored, except in the presence of the target sequence, which will bind to the single-stranded region present in the target binding domain and displace all or a portion of the target closing domain. The target binding domain and the target closing domain of a molecular torch include a detectable label or a pair of interacting labels (e.g., luminescent/quencher) positioned so that a different signal is produced when the molecular torch is self-hybridized than when the molecular torch is hybridized to the target sequence, thereby permitting detection of probe:target duplexes in a test sample in the presence of unhybridized molecular torches. Molecular torches and a variety of types of interacting label pairs are disclosed in U.S. Pat. No. 6,534,274, herein incorporated by reference in its entirety.
Another example of a detection probe having self-complementarity is a “molecular beacon.” Molecular beacons include nucleic acid molecules having a target complementary sequence, an affinity pair (or nucleic acid arms) holding the probe in a closed conformation in the absence of a target sequence present in an amplification reaction, and a label pair that interacts when the probe is in a closed conformation. Hybridization of the target sequence and the target complementary sequence separates the members of the affinity pair, thereby shifting the probe to an open conformation. The shift to the open conformation is detectable due to reduced interaction of the label pair, which may be, for example, a fluorophore and a quencher (e.g., DABCYL and EDANS). Molecular beacons are disclosed in U.S. Pat. Nos. 5,925,517 and 6,150,097, herein incorporated by reference in its entirety.
Other self-hybridizing probes are well known to those of ordinary skill in the art. By way of non-limiting example, probe binding pairs having interacting labels, such as those disclosed in U.S. Pat. No. 5,928,862 (herein incorporated by reference in its entirety) might be adapted for use in the present invention. Probe systems used to detect single nucleotide polymorphisms (SNPs) might also be utilized in the present invention. Additional detection systems include “molecular switches,” as disclosed in U.S. Publ. No. 20050042638, herein incorporated by reference in its entirety. Other probes, such as those comprising intercalating dyes and/or fluorochromes, are also useful for detection of amplification products in the present invention. See, e.g., U.S. Pat. No. 5,814,447 (herein incorporated by reference in its entirety).
In some embodiments of the present invention, hybridization is detected by enzymatic cleavage of specific structures (INVADER assay, Third Wave Technologies; See e.g., U.S. Pat. Nos. 5,846,717, 6,090,543; 6,001,567; 5,985,557; and 5,994,069; each of which is herein incorporated by reference). The INVADER assay detects specific DNA and RNA sequences by using structure specific enzymes to cleave a complex formed by the hybridization of overlapping oligonucleotide probes. Elevated temperature and an excess of one of the probes enable multiple probes to be cleaved for each target sequence present without temperature cycling. These cleaved probes then direct cleavage of a second labeled probe. The secondary probe oligonucleotide can be 5′-end labeled with fluorescein that is quenched by an internal dye. Upon cleavage, the de-quenched fluorescein labeled product may be detected using a standard fluorescence plate reader.
The INVADER assay detects specific mutations and SNPs in unamplified genomic DNA. The isolated DNA sample is contacted with the first probe specific either for a SNP/mutation or wild type sequence and allowed to hybridize. Then a secondary probe, specific to the first probe, and containing the fluorescein label, is hybridized and the enzyme is added. Binding is detected by using a fluorescent plate reader and comparing the signal of the test sample to known positive and negative controls.
In some embodiments, hybridization of a bound probe is detected using a TaqMan assay (PE Biosystems, Foster City, Calif.; See e.g., U.S. Pat. Nos. 5,962,233 and 5,538,848, each of which is herein incorporated by reference). The assay is performed during a PCR reaction. The TaqMan assay exploits the 5′-3′ exonuclease activity of the AMPLITAQ GOLD DNA polymerase. A probe, specific for a given allele or mutation, is included in the PCR reaction. The probe consists of an oligonucleotide with a 5′-reporter dye (e.g., a fluorescent dye) and a 3′-quencher dye. During PCR, if the probe is bound to its target, the 5′-3′ nucleolytic activity of the AMPLITAQ GOLD polymerase cleaves the probe between the reporter and the quencher dye. The separation of the reporter dye from the quencher dye results in an increase of fluorescence. The signal accumulates with each cycle of PCR and can be monitored with a fluorimeter.
In still further embodiments, polymorphisms are detected using the SNP-IT primer extension assay (Orchid Biosciences, Princeton, N.J.; See e.g., U.S. Pat. Nos. 5,952,174 and 5,919,626, each of which is herein incorporated by reference). In this assay, SNPs are identified by using a specially synthesized DNA primer and a DNA polymerase to selectively extend the DNA chain by one base at the suspected SNP location. DNA in the region of interest is amplified and denatured. Polymerase reactions are then performed using miniaturized systems called microfluidics. Detection is accomplished by adding a label to the nucleotide suspected of being at the SNP or mutation location. Incorporation of the label into the DNA can be detected by any suitable method (e.g., if the nucleotide contains a biotin label, detection is via a fluorescently labeled antibody specific for biotin).
In some embodiments, a MassARRAY system (Sequenom, San Diego, Calif.) is used to detect variant sequences (See e.g., U.S. Pat. Nos. 6,043,031; 5,777,324; and 5,605,798; each of which is herein incorporated by reference). DNA is isolated from blood samples using standard procedures. Next, specific DNA regions containing the mutation or SNP of interest, about 200 base pairs in length, are amplified by PCR. The amplified fragments are then attached by one strand to a solid surface and the non-immobilized strands are removed by standard denaturation and washing. The remaining immobilized single strand then serves as a template for automated enzymatic reactions that produce genotype specific diagnostic products.
Very small quantities of the enzymatic products, typically five to ten nanoliters, are then transferred to a SpectroCHIP array for subsequent automated analysis with the SpectroREADER mass spectrometer. Each spot is preloaded with light absorbing crystals that form a matrix with the dispensed diagnostic product. The MassARRAY system uses MALDI-TOF (Matrix Assisted Laser Desorption Ionization—Time of Flight) mass spectrometry. In a process known as desorption, the matrix is hit with a pulse from a laser beam. Energy from the laser beam is transferred to the matrix and it is vaporized resulting in a small amount of the diagnostic product being expelled into a flight tube. As the diagnostic product is charged when an electrical field pulse is subsequently applied to the tube they are launched down the flight tube towards a detector. The time between application of the electrical field pulse and collision of the diagnostic product with the detector is referred to as the time of flight. This is a very precise measure of the product's molecular weight, as a molecule's mass correlates directly with time of flight with smaller molecules flying faster than larger molecules. The entire assay is completed in less than one thousandth of a second, enabling samples to be analyzed in a total of 3-5 second including repetitive data collection. The SpectroTYPER software then calculates, records, compares and reports the genotypes at the rate of three seconds per sample.
In certain embodiments, endosymbiont nucleic acid is detected by sequencing methodologies. Illustrative non-limiting examples of nucleic acid sequencing techniques include, but are not limited to, chain terminator (Sanger) sequencing and dye terminator sequencing, as well as “next generation” sequencing techniques. Those of ordinary skill in the art will recognize that because RNA is less stable in the cell and more prone to nuclease attack experimentally RNA is usually reverse transcribed to DNA before sequencing.
Chain terminator sequencing uses sequence-specific termination of a DNA synthesis reaction using modified nucleotide substrates. Extension is initiated at a specific site on the template DNA by using a short radioactive, or other labeled, oligonucleotide primer complementary to the template at that region. The oligonucleotide primer is extended using a DNA polymerase, standard four deoxynucleotide bases, and a low concentration of one chain terminating nucleotide, most commonly a di-deoxynucleotide. This reaction is repeated in four separate tubes with each of the bases taking turns as the di-deoxynucleotide. Limited incorporation of the chain terminating nucleotide by the DNA polymerase results in a series of related DNA fragments that are terminated only at positions where that particular di-deoxynucleotide is used. For each reaction tube, the fragments are size-separated by electrophoresis in a slab polyacrylamide gel or a capillary tube filled with a viscous polymer. The sequence is determined by reading which lane produces a visualized mark from the labeled primer as you scan from the top of the gel to the bottom.
Dye terminator sequencing alternatively labels the terminators. Complete sequencing can be performed in a single reaction by labeling each of the di-deoxynucleotide chain-terminators with a separate fluorescent dye, which fluoresces at a different wavelength.
A set of methods referred to as “next-generation sequencing” techniques have emerged as alternatives to Sanger and dye-terminator sequencing methods (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; each herein incorporated by reference in their entirety). Next-generation sequencing (NGS) methods share the common feature of massively parallel, high-throughput strategies, with the goal of lower costs in comparison to older sequencing methods. NGS methods can be broadly divided into those that require template amplification and those that do not. Amplification-requiring methods include pyrosequencing commercialized by Roche as the 454 technology platforms (e.g., GS 20 and GS FLX), the Solexa platform commercialized by Illumina, and the Supported Oligonucleotide Ligation and Detection (SOLiD) platform commercialized by Applied Biosystems. Non-amplification approaches, also known as single-molecule sequencing, are exemplified by the HeliScope platform commercialized by Helicos BioSciences, and emerging platforms commercialized by VisiGen, Oxford Nanopore Technologies Ltd., and Pacific Biosciences, respectively.
In pyrosequencing (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; U.S. Pat. No. 6,210,891; U.S. Pat. No. 6,258,568; each herein incorporated by reference in its entirety), template DNA is fragmented, end-repaired, ligated to adaptors, and clonally amplified in-situ by capturing single template molecules with beads bearing oligonucleotides complementary to the adaptors. Each bead bearing a single template type is compartmentalized into a water-in-oil microvesicle, and the template is clonally amplified using a technique referred to as emulsion PCR. The emulsion is disrupted after amplification and beads are deposited into individual wells of a picotitre plate functioning as a flow cell during the sequencing reactions. Ordered, iterative introduction of each of the four dNTP reagents occurs in the flow cell in the presence of sequencing enzymes and luminescent reporter such as luciferase. In the event that an appropriate dNTP is added to the 3′ end of the sequencing primer, the resulting production of ATP causes a burst of luminescence within the well, which is recorded using a CCD camera. It is possible to achieve read lengths greater than or equal to 400 bases, and 1×106 sequence reads can be achieved, resulting in up to 500 million base pairs (Mb) of sequence.
In the Solexa/Illumina platform (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; U.S. Pat. No. 6,833,246; U.S. Pat. No. 7,115,400; U.S. Pat. No. 6,969,488; each herein incorporated by reference in its entirety), sequencing data are produced in the form of shorter-length reads. In this method, single-stranded fragmented DNA is end-repaired to generate 5′-phosphorylated blunt ends, followed by Klenow-mediated addition of a single A base to the 3′ end of the fragments. A-addition facilitates addition of T-overhang adaptor oligonucleotides, which are subsequently used to capture the template-adaptor molecules on the surface of a flow cell that is studded with oligonucleotide anchors. The anchor is used as a PCR primer, but because of the length of the template and its proximity to other nearby anchor oligonucleotides, extension by PCR results in the “arching over” of the molecule to hybridize with an adjacent anchor oligonucleotide to form a bridge structure on the surface of the flow cell. These loops of DNA are denatured and cleaved. Forward strands are then sequenced with reversible dye terminators. The sequence of incorporated nucleotides is determined by detection of post-incorporation fluorescence, with each fluor and block removed prior to the next cycle of dNTP addition. Sequence read length ranges from 36 nucleotides to over 50 nucleotides, with overall output exceeding 1 billion nucleotide pairs per analytical run.
Sequencing nucleic acid molecules using SOLiD technology (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; U.S. Pat. No. 5,912,148; U.S. Pat. No. 6,130,073; each herein incorporated by reference in their entirety) also involves fragmentation of the template, ligation to oligonucleotide adaptors, attachment to beads, and clonal amplification by emulsion PCR. Following this, beads bearing template are immobilized on a derivatized surface of a glass flow-cell, and a primer complementary to the adaptor oligonucleotide is annealed. However, rather than utilizing this primer for 3′ extension, it is instead used to provide a 5′ phosphate group for ligation to interrogation probes containing two probe-specific bases followed by 6 degenerate bases and one of four fluorescent labels. In the SOLiD system, interrogation probes have 16 possible combinations of the two bases at the 3′ end of each probe, and one of four fluors at the 5′ end. Fluor color and thus identity of each probe corresponds to specified color-space coding schemes. Multiple rounds (usually 7) of probe annealing, ligation, and fluor detection are followed by denaturation, and then a second round of sequencing using a primer that is offset by one base relative to the initial primer. In this manner, the template sequence can be computationally re-constructed, and template bases are interrogated twice, resulting in increased accuracy. Sequence read length averages 35 nucleotides, and overall output exceeds 4 billion bases per sequencing run.
In certain embodiments, nanopore sequencing in employed (see, e.g., Astier et al., J Am Chem Soc. 2006 Feb. 8; 128(5):1705-10, herein incorporated by reference). The theory behind nanopore sequencing has to do with what occurs when the nanopore is immersed in a conducting fluid and a potential (voltage) is applied across it: under these conditions a slight electric current due to conduction of ions through the nanopore can be observed, and the amount of current is exceedingly sensitive to the size of the nanopore. If DNA molecules pass (or part of the DNA molecule passes) through the nanopore, this can create a change in the magnitude of the current through the nanopore, thereby allowing the sequences of the DNA molecule to be determined.
HeliScope by Helicos BioSciences (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; U.S. Pat. No. 7,169,560; U.S. Pat. No. 7,282,337; U.S. Pat. No. 7,482,120; U.S. Pat. No. 7,501,245; U.S. Pat. No. 6,818,395; U.S. Pat. No. 6,911,345; U.S. Pat. No. 7,501,245; each herein incorporated by reference in their entirety) is the first commercialized single-molecule sequencing platform. This method does not require clonal amplification. Template DNA is fragmented and polyadenylated at the 3′ end, with the final adenosine bearing a fluorescent label. Denatured polyadenylated template fragments are ligated to poly(dT) oligonucleotides on the surface of a flow cell. Initial physical locations of captured template molecules are recorded by a CCD camera, and then label is cleaved and washed away. Sequencing is achieved by addition of polymerase and serial addition of fluorescently-labeled dNTP reagents. Incorporation events result in fluor signal corresponding to the dNTP, and signal is captured by a CCD camera before each round of dNTP addition. Sequence read length ranges from 25-50 nucleotides, with overall output exceeding 1 billion nucleotide pairs per analytical run.
Another exemplary nucleic acid sequencing approach developed by Stratos Genomics, Inc. that is also optionally adapted for use with the present invention involves the use of Xpandomers. This sequencing process typically includes providing a daughter strand produced by a template-directed synthesis. The daughter strand generally includes a plurality of subunits coupled in a sequence corresponding to a contiguous nucleotide sequence of all or a portion of a target nucleic acid in which the individual subunits comprise a tether, at least one probe or nucleobase residue, and at least one selectively cleavable bond. The selectively cleavable bond(s) is/are cleaved to yield an Xpandomer of a length longer than the plurality of the subunits of the daughter strand. The Xpandomer typically includes the tethers and reporter elements for parsing genetic information in a sequence corresponding to the contiguous nucleotide sequence of all or a portion of the target nucleic acid. Reporter elements of the Xpandomer are then detected. Additional details relating to Xpandomer-based approaches are described in, for example, U.S. Patent Publication No. 20090035777, entitled “HIGH THROUGHPUT NUCLEIC ACID SEQUENCING BY EXPANSION,” that was filed Jun. 19, 2008, which is incorporated herein in its entirety.
Other emerging single molecule sequencing methods include real-time sequencing by synthesis using a VisiGen platform (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; U.S. Pat. No. 7,329,492; U.S. patent application Ser. No. 11/671,956; U.S. patent application Ser. No. 11/781,166; each herein incorporated by reference in their entirety) in which immobilized, primed DNA template is subjected to strand extension using a fluorescently-modified polymerase and florescent acceptor molecules, resulting in detectible fluorescence resonance energy transfer (FRET) upon nucleotide addition.
Another real-time single molecule sequencing system developed by Pacific Biosciences (Voelkerding et al., Clinical Chem., 55: 641-658, 2009; MacLean et al., Nature Rev. Microbiol., 7: 287-296; U.S. Pat. No. 7,170,050; U.S. Pat. No. 7,302,146; U.S. Pat. No. 7,313,308; U.S. Pat. No. 7,476,503; all of which are herein incorporated by reference) utilizes reaction wells 50-100 nm in diameter and encompassing a reaction volume of approximately 20 zeptoliters (10×10−21 L). Sequencing reactions are performed using immobilized template, modified phi29 DNA polymerase, and high local concentrations of fluorescently labeled dNTPs. High local concentrations and continuous reaction conditions allow incorporation events to be captured in real time by fluor signal detection using laser excitation, an optical waveguide, and a CCD camera.
In certain embodiments, the single molecule real time (SMRT) DNA sequencing methods using zero-mode waveguides (ZMWs) developed by Pacific Biosciences, or similar methods, are employed. With this technology, DNA sequencing is performed on SMRT chips, each containing thousands of zero-mode waveguides (ZMWs). A ZMW is a hole, tens of nanometers in diameter, fabricated in a 100 nm metal film deposited on a silicon dioxide substrate. Each ZMW becomes a nanophotonic visualization chamber providing a detection volume of just 20 zeptoliters (10-21 liters). At this volume, the activity of a single molecule can be detected amongst a background of thousands of labeled nucleotides.
The ZMW provides a window for watching DNA polymerase as it performs sequencing by synthesis. Within each chamber, a single DNA polymerase molecule is attached to the bottom surface such that it permanently resides within the detection volume. Phospholinked nucleotides, each type labeled with a different colored fluorophore, are then introduced into the reaction solution at high concentrations which promote enzyme speed, accuracy, and processivity. Due to the small size of the ZMW, even at these high, biologically relevant concentrations, the detection volume is occupied by nucleotides only a small fraction of the time. In addition, visits to the detection volume are fast, lasting only a few microseconds, due to the very small distance that diffusion has to carry the nucleotides. The result is a very low background.
Processes and systems for such real time sequencing that may be adapted for use with the invention are described in, for example, U.S. Pat. No. 7,405,281, entitled “Fluorescent nucleotide analogs and uses therefor”, issued Jul. 29, 2008 to Xu et al., U.S. Pat. No. 7,315,019, entitled “Arrays of optical confinements and uses thereof”, issued Jan. 1, 2008 to Turner et al., U.S. Pat. No. 7,313,308, entitled “Optical analysis of molecules” , issued Dec. 25, 2007 to Turner et al., U.S. Pat. No. 7,302,146, entitled “Apparatus and method for analysis of molecules”, issued Nov. 27, 2007 to Turner et al., and U.S. Pat. No. 7,170,050, entitled “Apparatus and methods for optical analysis of molecules” , issued Jan. 30, 2007 to Turner et al., U.S. Patent Publications Nos. 20080212960, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Oct. 26, 2007 by Lundquist et al., 20080206764, entitled “Flowcell system for single molecule detection”, filed Oct. 26, 2007 by Williams et al., 20080199932, entitled “Active surface coupled polymerases”, filed Oct. 26, 2007 by Hanzel et al., 20080199874, entitled “CONTROLLABLE STRAND SCISSION OF MINI CIRCLE DNA”, filed Feb. 11, 2008 by Otto et al., 20080176769, entitled “Articles having localized molecules disposed thereon and methods of producing same”, filed Oct. 26, 2007 by Rank et al., 20080176316, entitled “Mitigation of photodamage in analytical reactions”, filed Oct. 31, 2007 by Eid et al., 20080176241, entitled “Mitigation of photodamage in analytical reactions”, filed Oct. 31, 2007 by Eid et al., 20080165346, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Oct. 26, 2007 by Lundquist et al., 20080160531, entitled “Uniform surfaces for hybrid material substrates and methods for making and using same”, filed Oct. 31, 2007 by Korlach, 20080157005, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Oct. 26, 2007 by Lundquist et al., 20080153100, entitled “Articles having localized molecules disposed thereon and methods of producing same”, filed Oct. 31, 2007 by Rank et al., 20080153095, entitled “CHARGE SWITCH NUCLEOTIDES”, filed Oct. 26, 2007 by Williams et al., 20080152281, entitled “Substrates, systems and methods for analyzing materials”, filed Oct. 31, 2007 by Lundquist et al., 20080152280, entitled “Substrates, systems and methods for analyzing materials”, filed Oct. 31, 2007 by Lundquist et al., 20080145278, entitled “Uniform surfaces for hybrid material substrates and methods for making and using same”, filed Oct. 31, 2007 by Korlach, 20080128627, entitled “SUBSTRATES, SYSTEMS AND METHODS FOR ANALYZING MATERIALS”, filed Aug. 31, 2007 by Lundquist et al., 20080108082, entitled “Polymerase enzymes and reagents for enhanced nucleic acid sequencing”, filed Oct. 22, 2007 by Rank et al., 20080095488, entitled “SUBSTRATES FOR PERFORMING ANALYTICAL REACTIONS”, filed Jun. 11, 2007 by Foquet et al., 20080080059, entitled “MODULAR OPTICAL COMPONENTS AND SYSTEMS INCORPORATING SAME”, filed Sep. 27, 2007 by Dixon et al., 20080050747, entitled “Articles having localized molecules disposed thereon and methods of producing and using same”, filed Aug. 14, 2007 by Korlach et al., 20080032301, entitled “Articles having localized molecules disposed thereon and methods of producing same”, filed Mar. 29, 2007 by Rank et al., 20080030628, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Feb. 9, 2007 by Lundquist et al., 20080009007, entitled “CONTROLLED INITIATION OF PRIMER EXTENSION”, filed Jun. 15, 2007 by Lyle et al., 20070238679, entitled “Articles having localized molecules disposed thereon and methods of producing same”, filed Mar. 30, 2006 by Rank et al., 20070231804, entitled “Methods, systems and compositions for monitoring enzyme activity and applications thereof”, filed Mar. 31, 2006 by Korlach et al., 20070206187, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Feb. 9, 2007 by Lundquist et al., 20070196846, entitled “Polymerases for nucleotide analogue incorporation”, filed Dec. 21, 2006 by Hanzel et al., 20070188750, entitled “Methods and systems for simultaneous real-time monitoring of optical signals from multiple sources”, filed Jul. 7, 2006 by Lundquist et al., 20070161017, entitled “MITIGATION OF PHOTODAMAGE IN ANALYTICAL REACTIONS”, filed Dec. 1, 2006 by Eid et al., 20070141598, entitled “Nucleotide Compositions and Uses Thereof”, filed Nov. 3, 2006 by Turner et al., 20070134128, entitled “Uniform surfaces for hybrid material substrate and methods for making and using same”, filed Nov. 27, 2006 by Korlach, 20070128133, entitled “Mitigation of photodamage in analytical reactions”, filed Dec. 2, 2005 by Eid et al., 20070077564, entitled “Reactive surfaces, substrates and methods of producing same”, filed Sep. 30, 2005 by Roitman et al., 20070072196, entitled “Fluorescent nucleotide analogs and uses therefore”, filed Sep. 29, 2005 by Xu et al., and 20070036511; entitled “Methods and systems for monitoring multiple optical signals from a single source”, filed Aug. 11, 2005 by Lundquist et al., and Korlach et al. (2008) “Selective aluminum passivation for targeted immobilization of single DNA polymerase molecules in zero-mode waveguide nanostructures” Proc. Nat'I. Acad. Sci. U.S.A. 105(4): 11761181—all of which are herein incorporated by reference in their entireties.
In certain embodiments, the present invention employs methods that employ determining at least partial base counts from endosymbionts. Methods of employing base compositions, databases containing base composition entries, and triangulation using primers, are described in the following patents, patent applications and scientific publications, all of which are herein incorporated by reference as if fully set forth herein: U.S. Pat. Nos. 7,108,974; 7,217,510; 7,226,739; 7,255,992; 7,312,036; 7,339,051; US patent publication numbers 2003/0027135; 2003/0167133; 2003/0167134; 2003/0175695; 2003/0175696; 2003/0175697; 2003/0187588; 2003/0187593; 2003/0190605; 2003/0225529; 2003/0228571; 2004/0110169; 2004/0117129; 2004/0121309; 2004/0121310; 2004/0121311; 2004/0121312; 2004/0121313; 2004/0121314; 2004/0121315; 2004/0121329; 2004/0121335; 2004/0121340; 2004/0122598; 2004/0122857; 2004/0161770; 2004/0185438; 2004/0202997; 2004/0209260; 2004/0219517; 2004/0253583; 2004/0253619; 2005/0027459; 2005/0123952; 2005/0130196 2005/0142581; 2005/0164215; 2005/0266397; 2005/0270191; 2006/0014154; 2006/0121520; 2006/0205040; 2006/0240412; 2006/0259249; 2006/0275749; 2006/0275788; 2007/0087336; 2007/0087337; 2007/0087338 2007/0087339; 2007/0087340; 2007/0087341; 2007/0184434; 2007/0218467; 2007/0218467; 2007/0218489; 2007/0224614; 2007/0238116; 2007/0243544; 2007/0248969; WO2002/070664; WO2003/001976; WO2003/100035; WO2004/009849; WO2004/052175; WO2004/053076; WO2004/053141; WO2004/053164; WO2004/060278; WO2004/093644; WO 2004/101809; WO2004/111187; WO2005/023083; WO2005/023986; WO2005/024046; WO2005/033271; WO2005/036369; WO2005/086634; WO2005/089128; WO2005/091971; WO2005/092059; WO2005/094421; WO2005/098047; WO2005/116263; WO2005/117270; WO2006/019784; WO2006/034294; WO2006/071241; WO2006/094238; WO2006/116127; WO2006/135400; WO2007/014045; WO2007/047778; WO2007/086904; WO2007/100397; and WO2007/118222, all of which are herein incorporated by reference.
Exemplary base-count related methods and other aspects of use in the methods, systems, and other aspects of the invention are also described in, for example, Ecker et al. (2005) “The Microbial Rosetta Stone Database: A compilation of global and emerging infectious microorganisms and bioterrorist threat agents” BMC Microbiology 5(1):19; Ecker et al. (2006) “The Ibis T5000 Universal Biosensor: An Automated Platform for Pathogen Identification and Strain Typing” JALA 6(10:341-351.; Ecker et al. (2006) “Identification of Acinetobacter species and genotyping of Acinetobacter baumannii by multilocus PCR and mass spectrometry” J Clin Microbiol. 44(8):2921-32; Ecker et al. (2005) “Rapid identification and strain-typing of respiratory pathogens for epidemic surveillance” Proc Natl Acad Sci USA. 102(22):8012-7; Hannis et al. (2008) “High-resolution genotyping of Campylobacter species by use of PCR and high-throughput mass spectrometry” J Clin Microbiol. 46(4):1220-5; Blyn et al. (2008) “Rapid detection and molecular serotyping of adenovirus by use of PCR followed by electrospray ionization mass spectrometry” J Clin Microbiol. 46(2):644-51; Sampath et al. (2007) “Global surveillance of emerging Influenza virus genotypes by mass spectrometry” PLoS ONE 2(5):e489; Sampath et al. (2007) “Rapid identification of emerging infectious agents using PCR and electrospray ionization mass spectrometry” Ann N Y Acad Sci. 1102:109-20; Hall et al. (2005) “Base composition analysis of human mitochondrial DNA using electrospray ionization mass spectrometry: a novel tool for the identification and differentiation of humans” Anal Biochem. 344(1):53-69; Hofstadler et al. (2003) “A highly efficient and automated method of purifying and desalting PCR products for analysis by electrospray ionization mass spectrometry” Anal Biochem. 316:50-57; Hofstadler et al. (2006) “Selective ion filtering by digital thresholding: A method to unwind complex ESI-mass spectra and eliminate signals from low molecular weight chemical noise” Anal Chem. 78(2):372-378.; and Hofstadler et al. (2005) “TIGER: The Universal Biosensor” Int J Mass Spectrom. 242(1):23-41, each of which is herein incorporated by reference in its entirety.
In certain embodiments, bioagent (e.g., endosymbiont) identifying amplicons amenable to molecular mass determination produced by the primers described herein are either of a length, size or mass compatible with a particular mode of molecular mass determination, or compatible with a means of providing a fragmentation pattern in order to obtain fragments of a length compatible with a particular mode of molecular mass determination. Such means of providing a fragmentation pattern of an amplicon include, but are not limited to, cleavage with restriction enzymes or cleavage primers, sonication or other means of fragmentation. Thus, in some embodiments, bioagent identifying amplicons are larger than 200 nucleobases and are amenable to molecular mass determination following restriction digestion. Methods of using restriction enzymes and cleavage primers are well known to those with ordinary skill in the art.
In some embodiments, amplicons corresponding to bioagent identifying amplicons are obtained using the polymerase chain reaction (PCR). Other amplification methods may be used such as ligase chain reaction (LCR), low-stringency single primer PCR, and multiple strand displacement amplification (MDA). (Michael, S F., Biotechniques (1994), 16:411-412 and Dean et al., Proc. Natl. Acad. Sci. U.S.A. (2002), 99, 5261-5266).
One embodiment of a process flow diagram used for endosymbiont primer selection and validation process is depicted in FIGS. 1 and 2. For each group of organisms, candidate target sequences are identified (200) from which nucleotide sequence alignments are created (210) and analyzed (220). Primers are then configured by selecting priming regions (230) to facilitate the selection of candidate primer pairs (240). The primer pair sequence is typically a “best fit” amongst the aligned sequences, such that the primer pair sequence may or may not be fully complementary to the hybridization region on any one of the bioagents in the alignment. Thus, best fit primer pair sequences are those with sufficient complementarity with two or more bioagents to hybridize with the two or more bioagents and generate an amplicon. The primer pairs are then subjected to in silico analysis by electronic PCR (ePCR) (300) wherein bioagent identifying amplicons are obtained from sequence databases such as GenBank or other sequence collections (310) and tested for specificity in silico (320). Bioagent identifying amplicons obtained from ePCR of GenBank sequences (310) may also be analyzed by a probability model which predicts the capability of a given amplicon to identify unknown bioagents. Preferably, the base compositions of amplicons with favorable probability scores are then stored in a base composition database (325). Alternatively, base compositions of the bioagent identifying amplicons obtained from the primers and GenBank sequences are directly entered into the base composition database (330). Candidate primer pairs (240) are validated by in vitro amplification by a method such as PCR analysis (400) of nucleic acid from a collection of organisms (410). Amplicons thus obtained are analyzed to confirm the sensitivity, specificity and reproducibility of the primers used to obtain the amplicons (420).
Synthesis of primers is well known and routine in the art. The primers may be conveniently and routinely made through the well-known technique of solid phase synthesis. Equipment for such synthesis is sold by several vendors including, for example, Applied Biosystems (Foster City, Calif.). Any other means for such synthesis known in the art may additionally or alternatively be employed.
The primers typically are employed as compositions for use in methods for identification of bioagents as follows: a primer pair composition is contacted with nucleic acid of an unknown isolate suspected of comprising an endosymbiont associated with a particular parasite. The nucleic acid is then amplified by a nucleic acid amplification technique, such as PCR for example, to obtain an amplicon that represents a bioagent identifying amplicon. The molecular mass of the strands of the double-stranded amplicon is determined by a molecular mass measurement technique such as mass spectrometry, for example. Preferably the two strands of the double-stranded amplicon are separated during the ionization process; however, they may be separated prior to mass spectrometry measurement. In some embodiments, the mass spectrometer is electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) or electrospray time of flight mass spectrometry (ESI-TOF-MS). A list of possible base compositions may be generated for the molecular mass value obtained for each strand, and the choice of the base composition from the list is facilitated by matching the base composition of one strand with a complementary base composition of the other strand. A measured molecular mass or base composition calculated therefrom is then compared with a database of molecular masses or base compositions indexed to primer pairs and to known bioagents. A match between the measured molecular mass or base composition of the amplicon and the database molecular mass or base composition for that indexed primer pair correlates the measured molecular mass or base composition with an indexed bioagent, thus identifying the unknown bioagent (e.g. the species of endosymbiont). In some embodiments, the primer pair used is at least one of the primer pairs of Table 3. In some embodiments, the method is repeated using a different primer pair to resolve possible ambiguities in the identification process or to improve the confidence level for the identification assignment (triangulation identification). In some embodiments, for example, where the unknown is a novel, previously uncharacterized organism, the molecular mass or base composition from an amplicon generated from the unknown is matched with one or more best match molecular masses or base compositions from a database to predict a family, genus, species, sub-type, etc. of the unknown. Such information may assist further characterization of the unknown or provide a physician treating a patient infected by the unknown with a therapeutic agent best calculated to treat the patient.
In certain embodiments, an endosymbiont associated with a particular parasite is detected with the systems and methods of the present invention in combination with other bioagents, including viruses, bacteria, fungi, or other bioagents. In particular embodiments, a panel is employed that includes endosymbionts and other related or un-related bioagents. Such panels may be specific for a particular type of bioagent, or specific for a specific type of test.
In some embodiments, a bioagent identifying amplicon may be produced using only a single primer (either the forward or reverse primer of any given primer pair), provided an appropriate amplification method is chosen, such as, for example, low stringency single primer PCR (LSSP-PCR).
In some embodiments, the oligonucleotide primers are broad range survey primers which hybridize to conserved regions of nucleic acid. The broad range primer may identify the unknown bioagent depending on which bioagent is in the sample. In other cases, the molecular mass or base composition of an amplicon does not provide sufficient resolution to identify the unknown bioagent as any one bioagent at or below the species level. These cases generally benefit from further analysis of one or more amplicons generated from at least one additional broad range survey primer pair, or from at least one additional division-wide primer pair, or from at least one additional drill-down primer pair. Identification of sub-species characteristics may be required, for example, to determine a clinical treatment of patient, or in rapidly responding to an outbreak of a new species, sub-type, etc. of pathogen to prevent an epidemic or pandemic.
One with ordinary skill in the art of design of amplification primers will recognize that a given primer need not hybridize with 100% complementarity in order to effectively prime the synthesis of a complementary nucleic acid strand in an amplification reaction. Primer pair sequences may be a “best fit” amongst the aligned bioagent sequences, thus they need not be fully complementary to the hybridization region of any one of the bioagents in the alignment. Moreover, a primer may hybridize over one or more segments such that intervening or adjacent segments are not involved in the hybridization event (e.g., for example, a loop structure or a hairpin structure). The primers may comprise at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% or at least 99% sequence identity with any of the primers listed in Table 3. Thus, in some embodiments, an extent of variation of 70% to 100%, or any range falling within, of the sequence identity is possible relative to the specific primer sequences disclosed herein. To illustrate, determination of sequence identity is described in the following example: a primer 20 nucleobases in length which is identical to another 20 nucleobase primer having two non-identical residues has 18 of 20 identical residues (18/20=0.9 or 90% sequence identity). In another example, a primer 15 nucleobases in length having all residues identical to a 15 nucleobase segment of primer 20 nucleobases in length would have 15/20=0.75 or 75% sequence identity with the 20 nucleobase primer. Percent identity need not be a whole number, for example when a 28 consecutive nucleobase primer is completely identical to a 31 consecutive nucleobase primer (28/31=0.9032 or 90.3% identical).
Percent homology, sequence identity or complementarity, can be determined by, for example, the Gap program (Wisconsin Sequence Analysis Package, Version 8 for Unix, Genetics Computer Group, University Research Park, Madison Wis.), using default settings, which uses the algorithm of Smith and Waterman (Adv. Appl. Math., 1981, 2, 482-489). In some embodiments, complementarity of primers with respect to the conserved priming regions of viral nucleic acid, is between about 70% and about 80%. In other embodiments, homology, sequence identity or complementarity, is between about 80% and about 90%. In yet other embodiments, homology, sequence identity or complementarity, is at least 90%, at least 92%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or is 100%.
In some embodiments, the primers described herein comprise at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 92%, at least 94%, at least 95%, at least 96%, at least 98%, or at least 99%, or 100% (or any range falling within) sequence identity with the primer sequences specifically disclosed herein.
In some embodiments, the oligonucleotide primers are 13 to 35 nucleobases in length (13 to 35 linked nucleotide residues). These embodiments comprise oligonucleotide primers 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35 nucleobases in length, or any range therewithin.
In some embodiments, any given primer comprises a modification comprising the addition of a non-templated T residue to the 5′ end of the primer (i.e., the added T residue does not necessarily hybridize to the nucleic acid being amplified). The addition of a non-templated T residue has an effect of minimizing the addition of non-templated A residues as a result of the non-specific enzyme activity of, e.g., Taq DNA polymerase (Magnuson et al., Biotechniques, 1996, 21, 700-709), an occurrence which may lead to ambiguous results arising from molecular mass analysis.
Primers may contain one or more universal bases. Because any variation (due to codon wobble in the third position) in the conserved regions among species is likely to occur in the third position of a DNA (or RNA) triplet, oligonucleotide primers can be designed such that the nucleotide corresponding to this position is a base which can bind to more than one nucleotide, referred to herein as a “universal nucleobase.” For example, under this “wobble” base pairing, inosine (I) binds to U, C or A; guanine (G) binds to U or C, and uridine (U) binds to U or C. Other examples of universal nucleobases include nitroindoles such as 5-nitroindole or 3-nitropyrrole (Loakes et al., Nucleosides and Nucleotides, 1995, 14, 1001-1003), the degenerate nucleotides dP or dK, an acyclic nucleoside analog containing 5-nitroindazole (Van Aerschot et al., Nucleosides and Nucleotides., 1995, 14, 1053-1056) or the purine analog 1-(2-deoxy-beta-D -ribofuranosyl)-imidazole-4-carboxamide (Sala et al., Nucl. Acids Res., 1996, 24, 3302-3306).
In some embodiments, to compensate for weaker binding by the wobble base, oligonucleotide primers are configured such that the first and second positions of each triplet are occupied by nucleotide analogs which bind with greater affinity than the unmodified nucleotide. Examples of these analogs include, but are not limited to, 2,6-diaminopurine which binds to thymine, 5-propynyluracil which binds to adenine and 5-propynylcytosine and phenoxazines, including G-clamp, which binds to G. Propynylated pyrimidines are described in U.S. Pat. Nos. 5,645,985, 5,830,653 and 5,484,908, each of which is commonly owned and incorporated herein by reference in its entirety. Propynylated primers are described in U.S Pre-Grant Publication No. 2003-0170682; also commonly owned and incorporated herein by reference in its entirety. Phenoxazines are described in U.S. Pat. Nos. 5,502,177, 5,763,588, and 6,005,096, each of which is incorporated herein by reference in its entirety. G-clamps are described in U.S. Pat. Nos. 6,007,992 and 6,028,183, each of which is incorporated herein by reference in its entirety.
In some embodiments, non-template primer tags are used to increase the melting temperature (Tm) of a primer-template duplex in order to improve amplification efficiency. A non-template tag is at least three consecutive A or T nucleotide residues on a primer which are not complementary to the template. In any given non-template tag, A can be replaced by C or G and T can also be replaced by C or G. Although Watson-Crick hybridization is not expected to occur for a non-template tag relative to the template, the extra hydrogen bond in a G-C pair relative to an A-T pair confers increased stability of the primer-template duplex and improves amplification efficiency for subsequent cycles of amplification when the primers hybridize to strands synthesized in previous cycles.
In other embodiments, propynylated tags may be used in a manner similar to that of the non-template tag, wherein two or more 5-propynylcytidine or 5-propynyluridine residues replace template matching residues on a primer. In other embodiments, a primer contains a modified internucleoside linkage such as a phosphorothioate linkage, for example.
In some embodiments, the primers contain mass-modifying tags. Reducing the total number of possible base compositions of a nucleic acid of specific molecular weight provides a means of avoiding a possible source of ambiguity in the determination of base composition of amplicons. Addition of mass-modifying tags to certain nucleobases of a given primer will result in simplification of de novo determination of base composition of a given bioagent identifying amplicon from its molecular mass.
In some embodiments, the mass modified nucleobase comprises one or more of the following: for example, 7-deaza-2′-deoxyadenosine-5-triphosphate, 5-iodo-2′-deoxyuridine-5′-triphosphate, 5-bromo-2′-deoxyuridine-5′-triphosphate, 5-bromo-2′-deoxycytidine-5′-triphosphate, 5-iodo-2′-deoxycytidine-5′-triphosphate, 5-hydroxy-2′-deoxyuridine-5′-triphosphate, 4-thiothymidine-5′-triphosphate, 5-aza-2′-deoxyuridine-5′-triphosphate, 5-fluoro-2′-deoxyuridine-5′-triphosphate, O6-methyl-2′-deoxyguanosine-5′-triphosphate, N2-methyl-2′-deoxyguanosine-5′-triphosphate, 8-oxo-2′-deoxyguanosine-5′-triphosphate or thiothymidine-5′-triphosphate. In some embodiments, the mass-modified nucleobase comprises 15N or 13C or both 13N and 13C.
In some embodiments, the molecular mass of a given bioagent (e.g., a species of endosymbiont) identifying amplicon is determined by mass spectrometry. Mass spectrometry is intrinsically a parallel detection scheme without the need for radioactive or fluorescent labels, because an amplicon is identified by its molecular mass. The current state of the art in mass spectrometry is such that less than femtomole quantities of material can be analyzed to provide information about the molecular contents of the sample. An accurate assessment of the molecular mass of the material can be quickly obtained, irrespective of whether the molecular weight of the sample is several hundred, or in excess of one hundred thousand atomic mass units (amu) or Daltons.
In some embodiments, intact molecular ions are generated from amplicons using one of a variety of ionization techniques to convert the sample to the gas phase. These ionization methods include, but are not limited to, electrospray ionization (ESI), matrix-assisted laser desorption ionization (MALDI) and fast atom bombardment (FAB). Upon ionization, several peaks are observed from one sample due to the formation of ions with different charges. Averaging the multiple readings of molecular mass obtained from a single mass spectrum affords an estimate of molecular mass of the bioagent identifying amplicon. Electrospray ionization mass spectrometry (ESI-MS) is particularly useful for very high molecular weight polymers such as proteins and nucleic acids having molecular weights greater than 10 kDa, since it yields a distribution of multiply-charged molecules of the sample without causing a significant amount of fragmentation.
The mass detectors used include, but are not limited to, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), time of flight (TOF), ion trap, quadrupole, magnetic sector, Q-TOF, and triple quadrupole.
In some embodiments, assignment of previously unobserved base compositions (also known as “true unknown base compositions”) to a given phylogeny can be accomplished via the use of pattern classifier model algorithms. Base compositions, like sequences, may vary slightly from strain to strain within species, for example. In some embodiments, the pattern classifier model is the mutational probability model. In other embodiments, the pattern classifier is the polytope model. A polytope model is the mutational probability model that incorporates both the restrictions among strains and position dependence of a given nucleobase within a triplet. In certain embodiments, a polytope pattern classifier is used to classify a test or unknown organism according to its amplicon base composition.
In some embodiments, it is possible to manage this diversity by building “base composition probability clouds” around the composition constraints for each species. A “pseudo four-dimensional plot” may be used to visualize the concept of base composition probability clouds. Optimal primer design typically involves an optimal choice of bioagent identifying amplicons and maximizes the separation between the base composition signatures of individual bioagents. Areas where clouds overlap generally indicate regions that may result in a misclassification, a problem which is overcome by a triangulation identification process using bioagent identifying amplicons not affected by overlap of base composition probability clouds.
In some embodiments, base composition probability clouds provide the means for screening potential primer pairs in order to avoid potential misclassifications of base compositions. In other embodiments, base composition probability clouds provide the means for predicting the identity of an unknown bioagent whose assigned base composition has not been previously observed and/or indexed in a bioagent identifying amplicon base composition database due to evolutionary transitions in its nucleic acid sequence. Thus, in contrast to probe-based techniques, mass spectrometry determination of base composition does not require prior knowledge of the composition or sequence in order to make the measurement.
Provided herein is bioagent classifying information at a level sufficient to identify a given bioagent. Furthermore, the process of determining a previously unknown base composition for a given bioagent (for example, in a case where sequence information is unavailable) has utility by providing additional bioagent indexing information with which to populate base composition databases. The process of future bioagent identification is thus improved as additional base composition signature indexes become available in base composition databases.
In some embodiments, the identity and quantity of an unknown bioagent may be determined using the process illustrated in FIG. 3. Primers (500) and a known quantity of a calibration polynucleotide (505) are added to a sample containing nucleic acid of an unknown bioagent. The total nucleic acid in the sample is then subjected to an amplification reaction (510) to obtain amplicons. The molecular masses of amplicons are determined (515) from which are obtained molecular mass and abundance data. The molecular mass of the bioagent identifying amplicon (520) provides for its identification (525) and the molecular mass of the calibration amplicon obtained from the calibration polynucleotide (530) provides for its quantification (535). The abundance data of the bioagent identifying amplicon is recorded (540) and the abundance data for the calibration data is recorded (545), both of which are used in a calculation (550) which determines the quantity of unknown bioagent in the sample.
In certain embodiments, a sample comprising an unknown bioagent is contacted with a primer pair which amplifies the nucleic acid from the bioagent, and a known quantity of a polynucleotide that comprises a calibration sequence. The amplification reaction then produces two amplicons: a bioagent identifying amplicon and a calibration amplicon. The bioagent identifying amplicon and the calibration amplicon are distinguishable by molecular mass while being amplified at essentially the same rate. Effecting differential molecular masses can be accomplished by choosing as a calibration sequence, a representative bioagent identifying amplicon (from a specific species of bioagent) and performing, for example, a 2-8 nucleobase deletion or insertion within the variable region between the two priming sites. The amplified sample containing the bioagent identifying amplicon and the calibration amplicon is then subjected to molecular mass analysis by mass spectrometry, for example. The resulting molecular mass analysis of the nucleic acid of the bioagent and of the calibration sequence provides molecular mass data and abundance data for the nucleic acid of the bioagent and of the calibration sequence. The molecular mass data obtained for the nucleic acid of the bioagent enables identification of the unknown bioagent by base composition analysis. The abundance data enables calculation of the quantity of the bioagent, based on the knowledge of the quantity of calibration polynucleotide contacted with the sample.
In some embodiments, construction of a standard curve in which the amount of calibration or calibrant polynucleotide spiked into the sample is varied provides additional resolution and improved confidence for the determination of the quantity of bioagent in the sample. Alternatively, the calibration polynucleotide can be amplified in its own reaction vessel or vessels under the same conditions as the bioagent. A standard curve may be prepared there from, and the relative abundance of the bioagent determined by methods such as linear regression. In some embodiments, multiplex amplification is performed where multiple bioagent identifying amplicons are amplified with multiple primer pairs which also amplify the corresponding standard calibration sequences. In this or other embodiments, the standard calibration sequences are optionally included within a single construct (preferably a vector) which functions as the calibration polynucleotide.
In some embodiments, the calibrant polynucleotide is used as an internal positive control to confirm that amplification conditions and subsequent analysis steps are successful in producing a measurable amplicon. Even in the absence of copies of the genome of a bioagent, the calibration polynucleotide gives rise to a calibration amplicon. Failure to produce a measurable calibration amplicon indicates a failure of amplification or subsequent analysis step such as amplicon purification or molecular mass determination. Reaching a conclusion that such failures have occurred is, in itself, a useful event. In some embodiments, the calibration sequence is comprised of DNA. In some embodiments, the calibration sequence is comprised of RNA.
In some embodiments, a calibration sequence is inserted into a vector which then functions as the calibration polynucleotide. In some embodiments, more than one calibration sequence is inserted into the vector that functions as the calibration polynucleotide. Such a calibration polynucleotide is herein termed a “combination calibration polynucleotide.” It should be recognized that the calibration method should not be limited to the embodiments described herein. The calibration method can be applied for determination of the quantity of any bioagent identifying amplicon when an appropriate standard calibrant polynucleotide sequence is designed and used.
In certain embodiments, primer pairs are configured to produce bioagent identifying amplicons within more conserved regions of an endosymbiont, while others produce bioagent identifying amplicons within regions that are may evolve more quickly. Primer pairs that characterize amplicons in a conserved region with low probability that the region will evolve past the point of primer recognition are useful, e.g., as a broad range survey-type primer. Primer pairs that characterize an amplicon corresponding to an evolving genomic region are useful, e.g., for distinguishing emerging bioagent strain variants.
The primer pairs described herein provide reagents for identifying parasites via their associated endosymbiont(s). Base composition analysis eliminates the need for prior knowledge of bioagent sequence to generate hybridization probes. Thus, in another embodiment, there is provided a method for determining the etiology of a particular stain when the process of identification of is carried out in a clinical setting, and even when a new strain is involved. This is possible because the methods may not be confounded by naturally occurring evolutionary variations.
Also provided are kits for carrying out the methods described herein. In some embodiments, the kit may comprise a sufficient quantity of one or more primer pairs to perform an amplification reaction on a target polynucleotide from a bioagent to form a bioagent identifying amplicon. In some embodiments, the kit may comprise from one to twenty primer pairs, from one to ten primer pairs, from one to eight pairs, from one to five primer pairs, from one to three primer pairs, or from one to two primer pairs. In some embodiments, the kit may comprise one or more primer pairs recited in Table 3. In certain embodiments, kits include all of the primer pairs recited in Table 3.
In some embodiments, the kit may also comprise a sufficient quantity of reverse transcriptase, a DNA polymerase, suitable nucleoside triphosphates (including any of those described above), a DNA ligase, and/or reaction buffer, or any combination thereof, for the amplification processes described above. A kit may further include instructions pertinent for the particular embodiment of the kit, such instructions describing the primer pairs and amplification conditions for operation of the method. In some embodiments, the kit further comprises instructions for analysis, interpretation and dissemination of data acquired by the kit. In other embodiments, instructions for the operation, analysis, interpretation and dissemination of the data of the kit are provided on computer readable media. A kit may also comprise amplification reaction containers such as microcentrifuge tubes, microtiter plates, and the like. A kit may also comprise reagents or other materials for isolating bioagent nucleic acid or bioagent identifying amplicons from amplification reactions, including, for example, detergents, solvents, or ion exchange resins which may be linked to magnetic beads. A kit may also comprise a table of measured or calculated molecular masses and/or base compositions of bioagents using the primer pairs of the kit.
The invention also provides systems that can be used to perform various assays relating to endosymbiont detection for parasite identification. In certain embodiments, systems include mass spectrometers configured to detect molecular masses of amplicons produced using purified oligonucleotide primer pairs described herein. Other detectors that are optionally adapted for use in the systems of the invention are described further below. In some embodiments, systems also include controllers operably connected to mass spectrometers and/or other system components. In some of these embodiments, controllers are configured to correlate the molecular masses of the amplicons with bioagents to effect detection or identification. In some embodiments, controllers are configured to determine base compositions of the amplicons from the molecular masses of the amplicons. As described herein, the base compositions generally correspond to the endosymbiont species identities. In certain embodiments, controllers include, or are operably connected to, databases of known molecular masses and/or known base compositions of amplicons of known species of endosymbiont produced with the primer pairs described herein. Controllers are described further below.
In some embodiments, systems include one or more of the primer pairs described herein (e.g., in Table 3). In certain embodiments, the oligonucleotides are arrayed on solid supports, whereas in others, they are provided in one or more containers, e.g., for assays performed in solution. In certain embodiments, the systems also include at least one detector or detection component (e.g., a spectrometer) that is configured to detect detectable signals produced in the container or on the support. In addition, the systems also optionally include at least one thermal modulator (e.g., a thermal cycling device) operably connected to the containers or solid supports to modulate temperature in the containers or on the solid supports, and/or at least one fluid transfer component (e.g., an automated pipettor) that transfers fluid to and/or from the containers or solid supports, e.g., for performing one or more assays (e.g:, nucleic acid amplification, real-time amplicon detection, etc.) in the containers or on the solid supports.
Detectors are typically structured to detect detectable signals produced, e.g., in or proximal to another component of the given assay system (e.g., in a container and/or on a solid support). Suitable signal detectors that are optionally utilized, or adapted for use, herein detect, e.g., fluorescence, phosphorescence, radioactivity, absorbance, refractive index, luminescence, or mass. Detectors optionally monitor one or a plurality of signals from upstream and/or downstream of the performance of, e.g., a given assay step. For example, detectors optionally monitor a plurality of optical signals, which correspond in position to “real-time” results. Example detectors or sensors include photomultiplier tubes, CCD arrays, optical sensors, temperature sensors, pressure sensors, pH sensors, conductivity sensors, or scanning detectors. Detectors are also described in, e.g., Skoog et al., Principles of Instrumental Analysis, 5th Ed., Harcourt Brace College Publishers (1998), Currell, Analytical Instrumentation: Performance Characteristics and Quality, John Wiley & Sons, Inc. (2000), Sharma et al., Introduction to Fluorescence Spectroscopy, John Wiley & Sons, Inc. (1999), Valeur, Molecular Fluorescence: Principles and Applications, John Wiley & Sons, Inc. (2002), and Gore, Spectrophotometry and Spectrofluorimetry: A Practical Approach, 2.sup.nd Ed., Oxford University Press (2000), which are each incorporated by reference.
As mentioned above, the systems of the invention also typically include controllers that are operably connected to one or more components (e.g., detectors, databases, thermal modulators, fluid transfer components, robotic material handling devices, and the like) of the given system to control operation of the components. More specifically, controllers are generally included either as separate or integral system components that are utilized, e.g., to receive data from detectors (e.g., molecular masses, etc.), to effect and/or regulate temperature in the containers, or to effect and/or regulate fluid flow to or from selected containers. Controllers and/or other system components are optionally coupled to an appropriately programmed processor, computer, digital device, information appliance, or other logic device (e.g., including an analog to digital or digital to analog converter as needed), which functions to instruct the operation of these instruments in accordance with preprogrammed or user input instructions, receive data and information from these instruments, and interpret, manipulate and report this information to the user. Suitable controllers are generally known in the art and are available from various commercial sources.
Any controller or computer optionally includes a monitor, which is often a cathode ray tube (“CRT”) display, a flat panel display (e.g., active matrix liquid crystal display or liquid crystal display), or others. Computer circuitry is often placed in a box, which includes numerous integrated circuit chips, such as a microprocessor, memory, interface circuits, and others. The box also optionally includes a hard disk drive, a floppy disk drive, a high capacity removable drive such as a writeable CD-ROM, and other common peripheral elements. Inputting devices such as a keyboard or mouse optionally provide for input from a user. These components are illustrated further below.
The computer typically includes appropriate software for receiving user instructions, either in the form of user input into a set of parameter fields, e.g., in a graphic user interface (GUI), or in the form of preprogrammed instructions, e.g., preprogrammed for a variety of different specific operations. The software then converts these instructions to appropriate language for instructing the operation of one or more controllers to carry out the desired operation. The computer then receives the data from, e.g., sensors/detectors included within the system, and interprets the data, either provides it in a user understood format, or uses that data to initiate further controller instructions, in accordance with the programming.
FIG. 4 is a schematic showing a representative system that includes a logic device in which various aspects of the present invention may be embodied. As will be understood by practitioners in the art from the teachings provided herein, aspects of the invention are optionally implemented in hardware and/or software. In some embodiments, different aspects of the invention are implemented in either client-side logic or server-side logic. As will be understood in the art, the invention or components thereof may be embodied in a media program component (e.g., a fixed media component) containing logic instructions and/or data that, when loaded into an appropriately configured computing device, cause that device to perform as desired. As will also be understood in the art, a fixed media containing logic instructions may be delivered to a viewer on a fixed media for physically loading into a viewer's computer or a fixed media containing logic instructions may reside on a remote server that a viewer accesses through a communication medium in order to download a program component.
More specifically, FIG. 4 schematically illustrates computer 1000 to which mass spectrometer 1002 (e.g., an ESI-TOF mass spectrometer, etc.), fluid transfer component 1004 (e.g., an automated mass spectrometer sample injection needle or the like), and database 1008 are operably connected. Optionally, one or more of these components are operably connected to computer 1000 via a server (not shown in FIG. 4). During operation, fluid transfer component 1004 typically transfers reaction mixtures or components thereof (e.g., aliquots comprising amplicons) from multi-well container 1006 to mass spectrometer 1002. Mass spectrometer 1002 then detects molecular masses of the amplicons. Computer 1000 then typically receives this molecular mass data, calculates base compositions from this data, and compares it with entries in database 1008 to identify species or strains of endosymbionts in a given sample. It will be apparent to one of skill in the art that one or more components of the system schematically depicted in FIG. 4 are optionally fabricated integral with one another (e.g., in the same housing).
EXAMPLES
The following example is provided to further illustrate aspects of the invention and it not intended to limit the present invention, but instead is an exemplary embodiment.
Example 1
Parasite Detection Via Endosymbiont Detection
This Example describes the detection of heartworm parasite (Dirofilaria immitis) in a sample by detecting the known endosymbiont Wolbachia—without ever directly detecting Dirofilaria immitis itself (e.g., not detecting an protein sequence, nucleic acid sequence, or host generated antibody from Dirofilaria immitis itself).
Heartworm positive and negative dog blood specimens were obtained from TRS Labs (295 Research Dr, Athens, Ga. 30605). Samples were extracted using TNA_Blood_1 mL_001.6 protocol. Samples were eluted in 200 uL of AVE buffer.









TABLE 2






ID
Sample








GV022510CC-1
545; infected with 50 dil3 



GV022510CC-2
288; infected with 50 dil3 



GV022510CC-3
571; infected with 50 dil3 



GV022510CC-4
275; IV transplanted with 10F + 10M 



GV022510CC-5
277; IV transplanted with 10F + 10M 



GV022510CC-6
666; negative



GV022510CC-7
964; negative



GV022510CC-8
965; negative



GV022510CC-9
966; negative



GV022510CC-10
967; negative









Samples GV022510CC-1, 2, and 6 were loaded into a TBS [v2] plate at 5 uL of sample per well and cycled on EPluto99 (A0007656/P05040103). The plate was analyzed for any unknown basecounts found in the two positive samples (1,2) but not in the negative sample (6) or a water blank.

The following five primer pairs, specific to Wolbachia endosymbiont of Dirofilaria immitis, shown in Table 3 were employed for amplification:














TABLE 3






Gene
forward
forward
SEQ
reverse
reverse
SEQ


pp code
target
primer name
primer sequence
ID NO:
primer name
primer sequence
ID NO:







BCT346
16S
16S_EC_713_732_TMOD_F
TAGAACACCGATGGC
1
16S_EC_789_809_TMOD_R
TCGTGGACTACCAGG
2



rRNA

GAAGGC


GTATCTA




gene








 


GCT348
16S
16S_EC_960_981_TMOD_F
TTTCGATGCAACGCG
3
16S_EC_1054_1073_TMOD_R
TACGAGCTGACGACA
4



rRNA

AAGAACCT


GCCATG




gene








 


BCT360
23S
23S_EC_2646_2667_TMOD_F
TCTGTTCTTAGTACG
5
23S_EC_2745_2765_TMOD_R
TTTCGTGCTTAGATG
6



rRNA

AGAGGACC


CTTTCAG




gene








 


BCT3569
GltA
GLTA_NC005956-747661-
TGCATGCAGATCATG
7
GLTA_NC005956-747661-
TCCATGTGCTGGTCC
8




746366_677_701_F
AACAAAATGC

746366_781_798_R
CCA



 


BCT3575
RpoB
RPOB_NC005956-709722-
TGCATCACTTGGTTG
9
RPOB_NC005956-709722-
TCACCAAAACGCTGA
10




713873_3782_3812_F
ATGATAAGATACATG

713873_3871_3893_R
CCACCAAA






C









Samples 1 and 2 both had high amounts of amplicon for PP BCT3569 and PP BCT3575 that were not observed in the negative sample. Samples were subjected to mass spectrometry and base counts were determined. Samples were also run on the TBS 5.0 plate. Samples GV022510CC-3, 4, and 7 were run on the TBS 5.0 plate (C00033324N00033324) with 10 uL of sample per well. Samples GV022510CC-3, and 4 showed the same signature for PP BCT3575 as the samples run on the TBS[v2] plate; A26G28C22T36. This signature was absent in sample 7 (negative blood).
PP BCT3569 had the basecount signature A29G34C25T34 in both samples 1 and 2 (FIG. 5). PP BCT3575 had the basecount signature A26G28C22T36 in both samples (FIG. 6). Neither one of these signatures was observed in the negative sample (GV02251OCC-5). There were unique signatures for the heartworm positive samples on primer pairs BCT346, BCT348, and BCT360. The basecount signature for BCT346 was A28G31C21T19 (FIG. 7). The basecount signature for BCT348 was A25G34C28T32 (FIG. 8). The basecount signature for BCT360 was A35G32C21T34 (FIG. 9). None of these basecounts were observed in the heartworm negative blood.
It is noted that the above basecounts could be part of a database such that, when a sample is tested, if the same basecount is located in an unknown sample, a user would know that Wolbachia associated with Dirofilaria immitis was present in the sample—thereby identifying that Dirofilaria immitis was present in the sample (or present in the subject being tested) without having to test for Dirofilaria immitis. 
Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference (including, but not limited to, journal articles, U.S. and non-U.S. patents, patent application publications, international patent application publications, gene bank accession numbers, internet web sites, and the like) cited in the present application is incorporated herein by reference in its entirety.

## Claims

1. A method of identifying a parasite in a subject comprising:
a) providing:
i) a blood sample from a human subject suspected of being infected with a parasite, wherein said parasite is associated with a specific Wolbachia species or subspecies endosymbiont; and
ii) a nucleic acid detection assay configured to detect nucleic acid from said endosymbiont wherein said nucleic acid detection assay comprises at least one primer pair, and said contacting generates endosymbiont amplicons using said primer pair under amplification conditions; and

b) contacting said sample with said nucleic acid detection assay under conditions such that the presence or absence of said Wolbachia species or subspecies endosymbiont in said sample is determined, wherein said presence of said Wolbachia species or subspecies endosymbiont uniquely identifies said subject as being infected with said parasite;
c) determining a partial base count of at least a subsequence of said endosymbiont amplicons to produce base count data; and
d) diagnosing said subject as being infected with said parasite based on said presence of said Wolbachia species or subspecies endosymbiont in said sample wherein said diagnosing is accomplished without directly detecting the presence of said parasite in said subject.

2. The method of claim 1, further comprising querying a database comprising at least one base count entry corresponding to an identified nucleic acid to produce a match of the base count data with the base count entry, thereby identifying said endosymbiont amplicon as from said endosymbiont.

3. The method of claim 1, wherein said determining a partial base count employs mass spectrometry.

4. The method of claim 1, wherein said determining a partial base count does not employ mass spectrometry.

5. The method of claim 1, wherein said nucleic acid detection assay is selected from the group consisting of: a fluorogenic 5′ nuclease assay, a sequencing assay, a polymerase chain reaction assay, a hybridization assay, a microarray assay, a bead array assay, a primer extension assay, an enzyme mismatch cleavage assay, a branched hybridization assay, a rolling circle replication assay, a molecular beacon assay, a cycling probe assay, a ligase chain reaction assay, a sandwich hybridization assay, an invasive cleavage assay, and a Line Probe Assay.

6. The method of claim 1, wherein said parasite is a nematode.

7. The method of claim 6, wherein said nematode infects dogs or cats.

8. The method of claim 6, wherein said nematode infects humans.

9. The method of claim 1, wherein said parasite is selected from the group consisting of: Dirofilaria immitis, Onchocerca volvulus, Wuchereria bancrofti, Brugia timori, and Brugia malayi.

10. The method of claim 1, wherein said nucleic acid detection assay comprises at least one primer pair, wherein said primer pair is selected from the group consisting of: SEQ ID NOs:1 and 2; SEQ ID NOs:3 and 4; SEQ ID NOs:5 and 6; SEQ ID NOs:7 and 8; and SEQ ID NOs: 9 and 10.

11. The method of claim 10, wherein said nucleic acid detection assay comprises at least one primer pair, wherein said primer pair is configured to hybridize with conserved regions of said endosymbiont nucleic acid that flank a variable region of said endosymbiont nucleic acid.

12. A system, comprising:
a) a mass spectrometer configured to detect one or more molecular masses of amplicons produced using at least one purified oligonucleotide primer pair that comprises forward and reverse primers, wherein said primer pair is configured to hybridize with conserved regions of Wolbachia nucleic acid that flank a variable region of nucleic acid specific for a Wolbachia species or subspecies endosymbiont;
b) a controller operably connected to said mass spectrometer, said controller configured to correlate said molecular masses of said amplicons with one or more Wolbachiaspecies or subspecies endosymbiont identities; and
c) a database of partial base counts wherein said database of partial base counts comprises partial base counts comprising the number of any one of four nucleobase types, any two of four nucleobase types, or any three of four nucleobase types.