bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic Characterization of a
Streptococcus mutans
LraI Family Operon and Role in Virulence
Authors: Kitten Todd , Munro Cindy L. , Michalek Suzanne M. , Macrina Francis L. 
Published: July 2002

ABSTRACT

Proteins belonging to the LraI (for “lipoprotein receptor antigen”) family function as adhesins in several streptococci, as a virulence factor for endocarditis in at least one of these species, and potentially as metal transporters in many bacteria. We have identified and characterized the chromosomal locus containing the LraI family gene (designated
sloC
) from
Streptococcus mutans
, an agent of dental caries and endocarditis in humans. Northern blot analysis indicated that
sloC
is cotranscribed with three other genes. As with other LraI operons, the
sloA
and
sloB
genes apparently encode components of an ATP-binding cassette transport system. The product of the fourth gene,
sloR
, has homology to the metal-dependent regulator from
Corynebacterium diphtheriae
, DtxR. A potential binding site for SloR was identified upstream from the
sloABCR
operon and was conserved upstream from LraI operons in several other streptococci. Potential SloR homologs were identified in the unfinished genomic sequences from two of these,
S. pneumoniae
and
S. pyogenes
. Mutagenesis of
sloC
in
S. mutans
resulted in apparent loss of expression of the entire operon as assessed by Northern blot analysis. The
sloC
mutant was indistinguishable from its wild-type parent in a gnotobiotic rat model of caries but was significantly less virulent in a rat model of endocarditis. Virulence for endocarditis was restored by correction of the
sloC
mutation but not by provision of the
sloC
gene in
trans
, suggesting that virulence requires the expression of other genes in the
sloC
operon.
Invasion of Epithelial Cells byYersinia pestis: Evidence for aY. pestis-Specific Invasin
Authors: Cowan Clarissa , Jones Heather A. , Kaya Yasemin H. , Perry Robert D. , Straley Susan C. 
Published: July 2002

ABSTRACTThe causative agent of plague,Yersinia pestis, is regarded as being noninvasive for epithelial cells and lacks the major adhesins and invasins of its enteropathogenic relativesYersinia enterocoliticaandYersinia pseudotuberculosis. However, there are studies indicating thatY. pestisinvades and causes systemic infection from ingestive and aerogenic routes of infection. Accordingly, we developed a gentamicin protection assay and reexamined invasiveness ofY. pestisfor HeLa cells. By optimizing this assay, we discovered thatY. pestisis highly invasive. Several factors, including the presence of fetal bovine serum, the configuration of the tissue culture plate, the temperature at which the bacteria are grown, and the presence of the plasminogen activator protease Pla-encoding plasmid pPCP1, were found to influence invasiveness strongly. Suboptimal combinations of these factors may have contributed to negative findings by previous studies attempting to demonstrate invasion byY. pestis. Invasion of HeLa cells was strongly inhibited by cytochalasin D and modestly inhibited by colchicine, indicating strong and modest respective requirements for microfilaments and microtubules. We found no significant effect of the iron status of yersiniae or of the pigmentation locus on invasion and likewise no significant effect of the Yops regulon. However, an unidentified thermally induced property (possibly theY. pestis-specific capsular protein Caf1) did inhibit invasiveness significantly, and the plasmid pPCP1, unique toY. pestis, was essential for highly efficient invasion. pPCP1 encodes an invasion-promoting factor and not just an adhesin, becauseY. pestislacking this plasmid still adhered to HeLa cells. These studies have enlarged our picture ofY. pestisbiology and revealed the importance of properties that are unique toY. pestis.
Expression of ExsA in
trans
Confers Type III Secretion System-Dependent Cytotoxicity on Noncytotoxic
Pseudomonas aeruginosa
Cystic Fibrosis Isolates
Authors: Dacheux Denis , Attree Ina , Toussaint Bertrand 
Published: July 2002

ABSTRACT

Twelve
Pseudomonas aeruginosa
cystic fibrosis isolates that are not able to exert a type III secretion system (TTSS)-dependent cytotoxicity towards phagocytes have been further studied. The strains, although possessing TTSS genes and
exsA
, which encodes a positive regulator of the TTSS regulon, showed no transcriptional activation of the
exsCBA
regulatory operon. The expression of
exsA
in trans restored the in vitro secretion of TTSS proteins and ex vivo cytotoxicity.
Mimicry of a G Protein Mutation by Pertussis Toxin Expression in Transgenic
Caenorhabditis elegans
Authors: Darby Creg , Falkow Stanley 
Published: July 2002

ABSTRACT

Pathogens produce virulence factors that interact directly with host molecules, but in many cases the host targets are unknown. The genetic and molecular identification of these orphan targets is often not feasible with mammalian experimental models. However, a substantial number of known targets are molecules and pathways that are conserved among eukaryotes, and therefore the use of nonmammalian model hosts to identify orphan targets may prove useful. To demonstrate the feasibility of this approach, we transformed the nematode
Caenorhabditis elegans
with a gene encoding the catalytic subunit of pertussis toxin (PTX), which in mammals inactivates G
o/i
α proteins. Expression of PTX in
C. elegans
produced phenotypes almost identical to those of a null mutation in the nematode gene encoding G
o/i
α. Furthermore, PTX suppressed the phenotype of a constitutively active form of nematode G
o/i
α protein. These results indicate that PTX is functional in nematodes and acts specifically on the
C. elegans
homologue of the mammalian target.
Transient Transgenic Expression of Gamma Interferon PromotesLegionella pneumophilaClearance in Immunocompetent Hosts
Authors: Deng Jane C. , Tateda Kazuhiro , Zeng Xianying , Standiford Theodore J. 
Published: July 2002

ABSTRACTGamma interferon (IFN-γ) and T1-phenotype immune responses are important components of host defense against a variety of intracellular pathogens, includingLegionella pneumophila. The benefit of intrapulmonary adenovirus-mediated IFN-γ gene therapy was investigated in a nonlethal murine model of experimentalL. pneumophilapneumonia. Intratracheal (i.t.) administration of 106CFU ofL. pneumophilainduced the expression of T1 phenotype cytokines, such as IFN-γ and interleukin-12 (IL-12). Natural killer cells were identified as the major cellular source of IFN-γ. To determine if enhanced expression of IFN-γ in the lung could promote pulmonary clearance ofL. pneumophila, we i.t. administered 5 × 108PFU of a recombinant adenovirus vector containing the murine IFN-γ cDNA (AdmIFN-γ) concomitant withL. pneumophila. We observed a 10-fold decrease in lung bacterial CFU at day 2 in the AdmIFN-γ-treated group compared to controls (P< 0.01). Alveolar macrophages isolated from AdmIFN-γ-treated animals displayed enhanced killing of intracellularL. pneumophilaorganisms ex vivo. Similar improvements in bacterial clearance were observed with i.t. recombinant IFN-γ treatment. The transient transgenic expression of IL-12, a known inducer of IFN-γ and promoter of T1-type immune responses, resulted in more modest improvement in bacterial clearance (sixfold reduction;P< 0.05). These results demonstrate that, even in immunocompetent hosts, exogenous administration or transient transgenic expression of IFN-γ, and to a lesser extent IL-12, may be of potential therapeutic benefit in the treatment of patients withLegionellapneumonia.
Bartonella henselae-Specific Cell-Mediated Immune Responses Display a Predominantly Th1 Phenotype in Experimentally Infected C57BL/6 Mice
Authors: Arvand Mardjan , Ignatius Ralf , Regnath Thomas , Hahn Helmut , Mielke Martin E. A. 
Published: July 2002

ABSTRACTImmune responses of the immunocompetent host toBartonella henselaeinfection were investigated in the murine infection model using C57BL/6 mice. Following intraperitoneal infection with human-derivedB. henselaestrain Berlin-1, viable bacteria could be recovered from livers and spleens during the first week postinfection, whileBartonellaDNA remained detectable by PCR in the liver for up to 12 weeks after infection. Granulomatous lesions developed in livers of infected mice, reached maximal density at 12 weeks after infection, and persisted for up to 20 weeks, indicating thatB. henselaeinduced a chronic granulomatous hepatitis in the immunocompetent murine host. T-cell-mediated immune responses were analyzed in vitro by means of spleen cell proliferation and cytokine release assays as well as analysis of immunoglobulin G (IgG) isotypes. Spleen cells from infected mice proliferated specifically upon stimulation with heat-killedBartonellaantigen. Proliferative responses were mainly mediated by CD4+T cells, increased during the course of infection, peaked at 8 weeks postinfection, and decreased thereafter. Gamma interferon, but not interleukin-4, was produced in vitro by spleen cells from infected animals upon stimulation withBartonellaantigens.Bartonella-specific IgG was detectable in serum of infected mice by 2 weeks, and the antibody concentration peaked at 12 weeks postinfection. IgG2b was the prominent isotype among theBartonella-specific serum IgG antibodies. These data indicate thatB. henselaeinduces cell-mediated immune responses with a Th1 phenotype in immunocompetent C57BL/6 mice.
Candida albicansIs Phagocytosed, Killed, and Processed for Antigen Presentation by Human Dendritic Cells
Authors: Newman Simon L. , Holly Angela 
Published: July 2002

ABSTRACTCandida albicansis a component of the normal flora of the alimentary tract and also is found on the mucocutaneous membranes of the healthy host.Candidais the leading cause of invasive fungal disease in premature infants, diabetics, and surgical patients, and of oropharyngeal disease in AIDS patients. As the induction of cell-mediated immunity toCandidais of critical importance in host defense, we sought to determine whether human dendritic cells (DC) could phagocytose and degradeCandidaand subsequently presentCandidaantigens to T cells. Immature DC obtained by culture of human monocytes in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 phagocytosed unopsonizedCandidain a time-dependent manner, and phagocytosis was not enhanced by opsonization ofCandidain serum. Like macrophages (Mφ), DC recognizedCandidaby the mannose-fucose receptor. Upon ingestion, DC killedCandidaas efficiently as human Mφ, and fungicidal activity was not enhanced by the presence of fresh serum. Although phagocytosis ofCandidaby DC stimulated the production of superoxide anion, inhibitors of the respiratory burst (or NO production) did not inhibit killing ofCandida, even when phagocytosis was blocked by preincubation of DC with cytochalasin D. Further, although apparently only modest phagolysosomal fusion occurred upon DC phagocytosis ofCandida, killing ofCandidaunder anaerobic conditions was almost equivalent to killing under aerobic conditions. Finally, DC stimulatedCandida-specific lymphocyte proliferation in a concentration-dependent manner after phagocytosis of both viable and heat-killedCandidacells. These data suggest that, in vivo, such interactions between DC andC. albicansmay facilitate the induction of cell-mediated immunity.
cDNA Array Analysis ofcagPathogenicity Island-AssociatedHelicobacter pyloriEpithelial Cell Response Genes
Authors: Cox Joanne M. , Clayton Christopher L. , Tomita Toshihiko , Wallace Don M. , Robinson Philip A. , Crabtree Jean E. 
Published: July 2002

ABSTRACTHelicobacter pyloristrains containing thecagpathogenicity island (PAI) induce NF-κB activation and interleukin-8 secretion in gastric epithelial cells. The aim of this study was to investigate changes in epithelial gene expression induced bycagPAI-positive and -negative strains ofH. pyloriusing high-density cDNA array hybridization technology. Radio-labeled cDNA prepared fromH. pylori-infected Kato 3 gastric epithelial cells was hybridized to high-density cDNA arrays to identify changes in epithelial gene expression compared to noninfected controls. In vivo expression of selected, differentially expressed genes was examined by reverse transcription-PCR analysis ofH. pylori-positive and -negative gastric mucosa. Screening of ca. 57,800 cDNAs identified 208 known genes and 48 novel genes and/or expressed sequence tags of unknown function to be differentially expressed in Kato 3 cells followingH. pyloriinfection. Marked differences in gene expression profiles were observed followingcagPAI-positive andcagPAI-negative infection with 15 novel cDNAs and 92 known genes being differentially expressed.H. pyloriwas found to change the expression of genes encoding growth factors and cytokine/chemokines and their receptors, apoptosis proteins, transcription factors and metalloprotease-disintegrin proteins (ADAMs), and tissue inhibitors of metalloproteinases. Gastric differential expression of selected known genes (amphiregulin and ADAM 10) and a novel gene (HPYR1) was confirmed in vivo in patients withH. pyloriinfection. Confirmation of the in vivo expression of selected genes demonstrates the usefulness of this approach for investigating pathogen-induced changes in host gene expression.
Role of
Streptococcus gordonii
Amylase-Binding Protein A in Adhesion to Hydroxyapatite, Starch Metabolism, and Biofilm Formation
Authors: Rogers Jeffrey D. , Palmer Robert J. , Kolenbrander Paul E. , Scannapieco Frank A. 
Published: July 2002

ABSTRACT

Interactions between bacteria and salivary components are thought to be important in the establishment and ecology of the oral microflora. α-Amylase, the predominant salivary enzyme in humans, binds to
Streptococcus gordonii
, a primary colonizer of the tooth. Previous studies have implicated this interaction in adhesion of the bacteria to salivary pellicles, catabolism of dietary starches, and biofilm formation. Amylase binding is mediated at least in part by the amylase-binding protein A (AbpA). To study the function of this protein, an erythromycin resistance determinant [
erm
(AM)] was inserted within the
abpA
gene of
S. gordonii
strains Challis and FAS4 by allelic exchange, resulting in
abpA
mutant strains Challis-E1 and FAS4-E1. Comparison of the wild-type and mutant strains did not reveal any significant differences in colony morphology, biochemical metabolic profiles, growth in complex or defined media, surface hydrophobicity, or coaggregation properties. Scatchard analysis of adhesion isotherms demonstrated that the wild-type strains adhered better to human parotid-saliva- and amylase-coated hydroxyapatite than did the AbpA mutants. In contrast, the mutant strains bound to whole-saliva-coated hydroxyapatite to a greater extent than did the wild-type strains. While the wild-type strains preincubated with purified salivary amylase grew well in defined medium with potato starch as the sole carbohydrate source, the AbpA mutants did not grow under the same conditions even after preincubation with amylase. In addition, the wild-type strain produced large microcolonies in a flow cell biofilm model, while the
abpA
mutant strains grew much more poorly and produced relatively small microcolonies. Taken together, these results suggest that AbpA of
S. gordonii
functions as an adhesin to amylase-coated hydroxyapatite, in salivary-amylase-mediated catabolism of dietary starches and in human saliva-supported biofilm formation by
S. gordonii.
Identification of Genes Induced In Vivo during
Klebsiella pneumoniae
CG43 Infection
Authors: Lai Yi-Chyi , Peng Hwei-Ling , Chang Hwan-You 
Published: July 2002

ABSTRACT

A novel in vivo expression technology (IVET) was performed to identify
Klebsiella pneumoniae
CG43 genes that are specifically expressed during infection of BALB/c mice. The IVET employed a UDP glucose pyrophosphorylase (
galU
)-deficient mutant of
K. pneumoniae
which is incapable of utilizing galactose and synthesizing capsular polysaccharide, as demonstrated by its low virulence to BALB/c mice and a white nonmucoid colony morphology on MacConkey-galactose agar. By using a functional
galU
gene as the reporter, an IVE promoter could render the
galU
mutant virulent while maintaining the white nonmucoid colony phenotype. A total of 20 distinct sequences were obtained through the in vivo selection. Five of them have been identified previously as virulence-associated genes in other pathogens, while another five with characterized functions are involved in regulation and transportation of nutrient uptake, biosynthesis of isoprenoids, and protein folding. No known functions have been attributed to the other 10 sequences. We have also demonstrated that 2 of the 20 IVE genes turn on under iron deprivation, whereas the expression of another five genes was found to be activated in the presence of paraquat, a superoxide generator.
Pertussis Toxin and Lipopolysaccharide Influence Phagocytosis ofBordetella pertussisby Human Monocytes
Authors: Schaeffer Lyndsay M. , Weiss Alison A. 
Published: July 2002

ABSTRACTThe potential of human monocytes to mediate the clearance ofBordetella pertussisinfection was examined. Bacteria expressing green fluorescent protein were incubated with adherent peripheral blood monocytes, and phagocytosis was quantified by using fluorescence microscopy. Monocytes internalized only a small percentage of the adherent bacteria. Surface-associated Bvg-regulated virulence factors, including adenylate cyclase toxin and filamentous hemagglutinin, did not affect attachment or phagocytosis. However, 1-h pretreatment with purified pertussis toxin inhibited the ability of monocytes to internalize wild-type bacteria. Mutations affecting the terminal trisaccharide of lipopolysaccharide resulted in reduced internalization without affecting adherence of bacteria to monocytes. Opsonization with human serum played only a modest role in promoting phagocytosis. The viability of internalized bacteria was determined by colony counts following treatment with polymyxin B and gentamicin. Less than 1% of internalized bacteria remained viable. These results suggest that pertussis toxin plays a role in the evasion of monocyte phagocytosis and that these cells represent a potential mediator of the clearance ofB. pertussisinfection.
Salmonella
DNA Adenine Methylase Mutants Elicit Protective Immune Responses to Homologous and Heterologous Serovars in Chickens
Authors: Dueger E. L. , House J. K. , Heithoff D. M. , Mahan M. J. 
Published: July 2002

ABSTRACT

Salmonella
DNA adenine methylase (Dam) mutants that lack or overproduce Dam are highly attenuated for virulence in mice and confer protection against murine typhoid fever. To determine whether vaccines based on Dam are efficacious in poultry, a
Salmonella
Dam
−
vaccine was evaluated in the protection of chicken broilers against oral challenge with homologous and heterologous
Salmonella
serovars. A
Salmonella enterica
serovar Typhimurium Dam
−
vaccine strain was attenuated for virulence in day-of-hatch chicks more than 100,000-fold. Vaccination of chicks elicited cross-protective immune responses, as evidenced by reduced colonization (10- to 10,000-fold) of the gastrointestinal tract (ileum, cecum, and feces) and visceral organs (bursa and spleen) after challenge with homologous (Typhimurium F98) and heterologous (Enteritidis 4973 and
S. enterica
O6,14,24: e,h-monophasic)
Salmonella
serovars that are implicated in
Salmonella
infection of poultry. The protection conferred was observed for the organ or the maximum CFU/tissue/bird as a unit of analysis, suggesting that Dam mutant strains may serve as the basis for the development of efficacious poultry vaccines for the containment of
Salmonella
.
Capsular Reactions ofCryptococcus neoformanswith Polyspecific and Oligospecific Polyclonal Anticapsular Antibodies
Authors: MacGill Tracy C. , MacGill Randall S. , Kozel Thomas R. 
Published: July 2002

ABSTRACTMonoclonal antibodies to the capsular polysaccharide ofCryptococcus neoformansproduce distinct capsular reactions and have biological activities that are determined by serotype specificity. In the present study, polyclonal rabbit anticapsular antibodies were cross-absorbed to produce serotype specificities similar to those of monoclonal antibodies. The results showed that polyclonal and monoclonal antibodies with similar serotype specificities have similar capsular reactions and biological activities.
C-Terminal Invariable Domain of VlsE May Not Serve as Target for Protective Immune Response againstBorrelia burgdorferi
Authors: Liang Fang Ting , Jacobs Mary B. , Philipp Mario T. 
Published: July 2002

ABSTRACTVlsE, the variable surface antigen of the Lyme disease spirochete,Borrelia burgdorferi, contains two invariable domains, at the amino and carboxyl termini, respectively, which collectively account for approximately one-half of the entire molecule's length and remain unchanged during antigenic variation. It is not known if these two invariable domains are exposed at the surface of either the antigen or the spirochete. If they are exposed at the spirochete's surface, they may elicit a protective immune response againstB. burgdorferiand serve as vaccine candidates. In this study, a 51-mer synthetic peptide that reproduced the entire sequence of the C-terminal invariable domain of VlsE was conjugated to the carrier keyhole limpet hemocyanin and used to immunize mice. Generated mouse antibody was able to immunoprecipitate native VlsE extracted from culturedB. burgdorferiB31 spirochetes, indicating that the C-terminal invariable domain was exposed at the antigen's surface. However, this domain was inaccessible to antibody binding at the surface of cultured intact spirochetes, as demonstrated by both an immunofluorescence experiment and an in vitro killing assay. Mouse antibody to the C-terminal invariable domain was not able to confer protection againstB. burgdorferiinfection, indicating that this domain was unlikely exposed at the spirochete's surface in vivo. We concluded that the C-terminal invariable domain was exposed at the antigen's surface but not at the surface of either cultured or in vivo spirochetes and thus cannot elicit protection againstB. burgdorferiinfection.