COMPARATIVE PHENOTYPE ANALYSIS FOR ASSESSMENT OF BIOLOGICALLY ACTIVE COMPOUNDS SUCH AS ANTIMICROBIALS

Abstract: The present invention relates to using multitest panels to improve the effectiveness, throughput, and efficiency of testing and commercial development of biologically active compounds, in particular those useful in human, animal, and plant health. In particular, the present invention provides phenotype microarrays suitable for testing biologically active compounds for their potential application in clinical, veterinary, and plant health.

Description: COMPARATIVE PHENOTYPE ANALYSIS FOR ASSESSMENT OF BIOLOGICALLY ACTIVE COMPOUNDS SUCH AS ANTIMICROBIALS FIELD OF THE INVENTION The present invention relates to using multitest panels to improve the effectiveness, throughput, and efficiency of testing and commercial development of biologically active compounds, in particular those useful in human, animal, and plant health. BACKGROUND OF THE INVENTION Biologically active chemicals (BACs) constitute major, important commercial product lines. These compounds are generally focused toward enhancing the health of humans, other animals and plants. The largest markets are for drugs, especially antimicrobials and pharmaceuticals for human use. Because of the large market, major efforts and expenditures are made annually, in the pursuit of better and more effective BACs. Antimicrobials constitute a major category of BACs. Although many antimicrobials have been developed and marketed, there remains a critical need for novel antimicrobials acting at novel targets. To some extent, this need is driven by the rapid emergence of antimicrobial-resistant pathogens. The appearance of strains resistant to all available drugs (e.g., enterococci), and the lag in the discovery of new antimicrobials has resulted in a renewed search for compounds effective against these resistant organisms. Despite this critical need and substantial research efforts, no new chemical entity has been approved by the U.S. Food and Drug Administration (FDA) for bacterial disease treatment for more than 20 years (Trias and Gordon, Curr. Opin. Biotechnol., 8:757-762 [1997]; See also, Bianchi and Baneyx, Appl. Environ. Microbiol., 65:5023-5027 [1999]). The situation is particularly desperate in the area of nosocomial infections, as infections with methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin- resistant Enterococcus faecium (VRE) have increased in frequency. There is a very real fear that high-level vancomycin resistance will spread within the staphylococci. Indeed, since 1996, vancomycin- intermediate S. aureus isolates (VISA; with vancomycin minimum inhibitory concentration [MIC] of 8-16 μg/ml), have been identified in Europe, Asia, and the U.S. This emergence of reduced vancomycin susceptibility in S. aureus increases the chances that some strains will become fully resistant, and currently used antimicrobials will become ineffective against such strains. This is of special concern because the emergence of community-acquired MRS A infections, has led to the increasing use of vancomycin against these organisms. Because very few therapies are available for treatment of MRSA, the confirmed reports of VISA strains demonstrating reduced susceptibility to vancomycin, the drug of last resort to treat MRSA, is of great concern (See e.g., Khurshid et al, MMWR, 48:1165-1167 [2000]; See also, Baughman et al.. MMWR 48:1167-1171 [2000]). Currently, the most commonly used antimicrobials are directed against a surprisingly small number of cellular functions as targets (e.g., cell wall, DNA, RNA, and protein biosynthesis). Table 1 summarizes these targets, gene products, and some antimicrobial classes that interact with the targets currently used. Instances of organism resistance to these antimicrobials are well-documented and widespread. Thus, it is clear that new antimicrobials are needed to counter the problem of increasing antimicrobial resistance. The efforts to discover new, effective antimicrobials involve two steps. In the first step, one or more drug targets are defined. Targeting of new pathways beyond those shown in Table 1 will likely play an important role in this stage of development. In the second step, potentially active chemicals are screened and evaluated to find those that have the desired activity without engendering undesirable side effects. Table 1. Targets of Some Widely Used Antimicrobials* Another major category of BACs are pharmaceuticals (i.e., drugs) designed to counteract human diseases. Diseases can be viewed as abnormalities in physiological pathways of cells. The main components of these pathways are proteins (enzymes, receptors, etc.) encoded by genes and expressed within the cells affected by the disease. Drugs usually exert their pharmaceutical effect by interacting with key proteins (i.e., drug targets) to restore the normal functioning of the protein or to inactivate the protein and compensate for a physiological pathway abnormality. As with antimicrobials, the process of developing pharmaceuticals involves two steps: (1) defining drug targets and then, (2) screening potential active chemicals to find the ones that specifically interact with the target to produce the desired effect without undesirable side effects. Although much work has been done in this area, there remains a need for improvements in the efficiency and effectiveness of the screening and evaluation of these chemicals. In response to the pressures to generate more promising drugs, pharmaceutical and biotechnology companies have turned toward more rapid high-throughput methods to find and evaluate lead compounds. These lead compounds are typically selected by screening large libraries of compounds compiled from a wide variety of sources, using collections of extracts, chemicals synthesized by combinatorial chemistry approaches, or through rational drug design. However, these methods have been a mixed blessing. Technologies such as combinatorial chemistry allow for rapid generation and screening of libraries of compounds against potential drug targets. Unfortunately, these technologies only look at the effect of the drugs on the proposed target, and they do not measure the effect on other cellular processes. A chemical may be an excellent candidate based on its interaction with the target protein, but it may also interact with other proteins in the cell and cause side effects. Thus, a major problem remains, in that the drug developer must sort through promising drug candidates to see how they effect other aspects of cell function, as well as how the drug candidates interact with other drugs that may be used simultaneously. Despite advances in these fields, there remains a need for highly sensitive and specific, yet cost-effective and easy-to-use methods for the identification and development of BACs that are effective in the treatment of disease. SUMMARY OF THE INVENTION The present invention relates to using multitest panels to improve the effectiveness, throughput, and efficiency of testing and commercial development of biologically active compounds, in particular those useful in human, animal, and plant health. The present invention provides methods for testing the response of at least two cells to at least one biologically active chemical comprising the steps of: a) providing: a testing device having at least two wells, wherein each well of the testing device contains a defined medium comprising at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates; a first suspension comprising a first cell and at least one biologically active chemical; and a second suspension comprising a second cell and at least one biologically active chemical; (b) inoculating the suspension into the wells of the testing device; and (c) observing the response of the first and second cells to at least one biologically active chemical. In some embodiments of the methods, the testing device is selected from the group consisting of microtiter plates and microcards. In other embodiments, the suspension further comprises a gelling agent. In still further embodiments, the testing device further comprises a gel-initiating agent in the wells. In some embodiments, the suspension further comprises a colorimetric indicator, while in other embodiments, the testing device further comprises a colorimetric indicator in the wells, and in other embodiments, the suspension and wells of the testing device both contain a colorimetric indicator. In some preferred embodiments, the observing is visual, while in other preferred embodiments, the observing is performed by an instrument. In some particularly preferred embodiments, the response of the first and second cells is non- radioactive. In alternative embodiments, the first and second cells are eukaryotic cells. In some preferred embodiments, the eukaryotic cells are animal cells, while in other preferred embodiments, the animal cells are mammalian cells, and in some particularly preferred embodiments, the mammalian cells are human cells. In some embodiments, the mammalian cells are mutant cells. In still further embodiments, the first and second cells are fungal cells, while in other embodiments, the first and second cells are prokaryotic cells. In some preferred embodiments, the drug comprises at least one antimicrobial. The present invention further provides methods for comparing the effect of at least two biologically active chemicals comprising: a) providing a first cell suspension comprising at least one cell type and at least one biologically active chemical, a second cell suspension comprising the same cell type as the first cell suspension and at least one biologically active chemical wherein the biologically active chemical is different from the biologically active chemical in the first cell suspension, a first testing device having wells, wherein the wells contain defined medium comprising at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates a second testing device having wells, wherein the wells contain at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates; b) adding the first cell suspension to the wells of the first testing device to provide a first phenotype array; c) adding the second cell suspension to the wells of the second testing device to provide a second phenotype array; d) incubating the first and second phenotype arrays; e) observing the response of the cell suspension in the first and the second phenotype arrays; and f) comparing the response of the cell suspension in the first phenotype array with the response of the cell suspension in the second phenotype array. In some embodiments of the methods, the testing device is selected from the group consisting of microtiter plates and microcards. In other embodiments, the suspension further comprises a gelling agent. In still further embodiments, the testing device further comprises a gel-initiating agent in the wells. In some embodiments, the suspension further comprises a colorimetric indicator, while in other embodiments, the testing device further comprises a colorimetric indicator in the wells, and in other embodiments, the suspension and wells of the testing device both contain a colorimetric indicator. In some preferred embodiments, the observing is visual, while in other preferred embodiments, the observing is performed by an instrument. In some particularly preferred embodiments, the response of the first and second cells is non- radioactive. In alternative embodiments, the first and second cells are eukaryotic cells. In some preferred embodiments, the eukaryotic cells are animal cells, while in other preferred embodiments, the animal cells are mammalian cells, and in some particularly preferred embodiments, the mammalian cells are human cells. In some embodiments, the mammalian cells are mutant cells. In still further embodiments, the first and second cells are fungal cells, while in other embodiments, the first and second cells are prokaryotic cells. In some preferred embodiments, the drug comprises at least one antimicrobial. In some embodiments, the testing device contains the same substrates as the second testing device. In still further embodiments, the comparison of the response is performed using multi-dimensional pattern analysis. The present invention further provides methods for testing the response of an organism to at least one biologically active chemical comprising the steps of: a) providing a testing device having at least two wells, wherein each well of the testing device contains at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, antimicrobials, and chromogenic testing substrates; and a suspension comprising an organism and at least one biologically active chemical; b) inoculating the suspension into the wells of the testing device; and c) observing the response of the organism to the biologically active chemical(s). In some embodiments, the testing device is selected from the group consisting of microtiter plates and microcards. In other embodiments, the suspension further comprises a gelling agent. In still other embodiments, the testing device further comprises a gel-initiating agent in the wells. In some preferred embodiments, the suspension further comprises a colorimetric indicator, while in other preferred embodiments the testing device further comprises a colorimetric indicator in the wells. In further embodiments, the observing is visual, while in other particularly preferred embodiments, the observing is performed by an instrument. The present invention also provides methods for comparing the effect of at least two biologically active chemicals comprising the steps of: a) providing a first cell suspension comprising an organism and at least one biologically active chemical, a second cell suspension comprising the same organism as in the first cell suspension and at least one biologically active chemical, wherein the biologically active chemical is different from the biologically active chemical in the first cell suspension; a first testing device having wells, wherein the wells contain at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, antimicrobials, and chromogenic testing substrates; a second testing device having wells, wherein the wells contain at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, antimicrobials, and chromogenic testing substrates; b) adding the cell suspension to the wells of the first testing device to provide a first phenotype array; c) adding the cell suspension to the wells of the second testing device to provide a second phenotype array; d) incubating the first and second phenotype arrays; e) observing the response of the cell suspension in the first and the second phenotype arrays; and f) comparing the response of the cell suspension in the first phenotype array with the response of the cell suspension in the second phenotype array. In some embodiments, the first and second testing devices are selected from the group consisting of microtiter plates and microcards. In other embodiments, the first and second cell suspensions further comprise a gelling agent. In still other embodiments, the first and second testing devices further comprise a gel-initiating agent in the wells. In some preferred embodiments, the first and second cell suspensions further comprise a colorimetric indicator, while in other embodiments the first and second testing devices further comprise a colorimetric indicator in the wells. In some particularly preferred embodiments, the first testing device contains the same substrates as the second testing device. In some preferred embodiments, the observing is performed visually, while in alternative preferred embodiments, the observing is performed by an instrument. In particularly preferred embodiments, the comparison of the response is performed using multi-dimensional pattern analysis. The present invention also provides multiwell kits for testing the effect of at least one biologically active chemical comprising: at least one testing device having at least two wells, wherein the wells contain at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorous sources, sulfur sources, growth stimulating nutrients, antimicrobials, and chromogenic substrates; and a cell suspension medium containing at least one biologically active chemical. In some embodiments, the testing device is selected from the group consisting of microtiter plates and microcards. In some preferred embodiments, the cell suspension medium comprises a gelling agent, while in other embodiments the testing device comprises a gel-initiating agent in the wells. In some embodiments, the cell suspension further comprises a colorimetric indicator, while in still other embodiments, the testing device further comprises a colorimetric indicator in the wells. DESCRIPTION OF THE FIGURES Figure 1 provides a simple schematic of one embodiment of the present invention in which a drug target in a cell is inactivated by the addition of a drug to the cell. This testing is performed using PMs. Figure 2 provides a simple schematic of one embodiment of the present invention in which synergistic and antagonistic drug interactions are detected and characterized. This testing is also performed using PMs. Figure 3 provides a simplified schematic of the environmental conditions in various wells within a microtiter plate and the effect of these conditions on the cells within the wells. Figure 4 provides a dendrogram showing the response of E. coli to various antimicrobials. DESCRIPTION OF THE INVENTION The present invention relates to using multitest panels, referred to herein as "phenotype microarrays," or "PMs," to improve the effectiveness, throughput, and efficiency of testing and commercial development of biologically active compounds (BACs), in particular those useful in human, animal, and plant health. Although particularly preferred embodiments of the present invention involve BACs such as antimicrobials and other compounds commonly used to treat disease or disease symptoms, the present invention also encompasses a wide range of BACs, including but not limited to nutrients, hormones, growth stimulating compounds, nutritional supplements, vitamins, metabolism-modifying compounds, insecticides, rodenticides, fungicides, herbicides, algicides, etc. It is further intended that the present invention encompasses BACs from any source. Thus, the present invention provides means to assess BACs from any source as well as for any suitable application. As indicated above, major problems are associated with traditional methods utilized in drug discovery and development. For example, a major problem remains, in that the drug developer must first sort through drug candidates to find the promising ones and then sort through the promising drug candidates to see how they effect other aspects of cell function, as well as how they interact with other drugs that may be used simultaneously. The present invention provides methods to test this efficiently and effectively, since PMs provide cost-effective and rapid, physiologically-based analyses of in vivo drug activity. In addition to aiding the screening of chemical libraries in an efficient, high- throughput manner, the present invention also finds use in detailed toxicological analyses. For example, it is contemplated that in assays utilizing mammalian cells, a battery of cell lines representing various organs are used to assay multiple drug candidates in an easy- to-use, high-throughput, rapid, and cost-effective manner. Based on these results, compounds that initially look promising, but that in fact cause unacceptable side effects can be eliminated from consideration before the start of costly clinical trials. Importantly, the present invention also provides methods for the analysis of drugs used in combination. The advantages of this embodiment include the ability to assess the likely interaction of multiple drugs in vivo. For example, in some cases, drug combinations exert harmful or antagonistic interactions, while in other cases, drug combinations act synergistically to provide additional benefit to the patient. Examples of the latter include combinations such as sulfa drugs with trimethoprim, and penicillins with β-lactamase inhibitors. As cost is always a consideration in the development of drugs and treatment regimens, the present invention provides distinct advantages over presently used methods. The present invention represents a significant time and cost savings for the development of drugs. For example, current estimates indicate that it currently takes an average of 14.9 years to develop a drug from first synthesis to final Food and Drug Administration (FDA) approval (See, R. Hansen, University of Rochester; S.N. Wigging, Texas A&M University; J. A. Dimasi, Tufts University Office of Technology Assessment, in Healthcare Marketplace Guide Research Reports 2000, 15th edition, volume 1, Dorland's Biomedical, Philadelphia, PA 19102, [1999-2000], at page 1-172). The cost of developing a single new drug has been reported to have grown from $54 million in 1976 to the current average of $359 million (Hansen supra). In addition, billions of dollars are wasted because approximately nine out of ten drugs fail during the course of clinical trials (Hansen, supra). The ability to efficiently identify and characterize new drug candidates, as well as eliminate unsatisfactory candidates early in the drug discovery process can save pharmaceutical companies billions of dollars on an annual basis. The present invention also provides methods and compositions suitable for determining the mode of action of a BAC of interest. In this embodiment, the invention utilizes PMs in broad assays of various cell functions. This allows the determination of which functions are most sensitively altered by the BAC. For example, if a BAC is shown to inhibit cell wall synthesis (e.g., vancomycin), the level of synergy between this test BAC and other BACs that also inhibit cell wall synthesis (e.g., cephalosporins, penicillins, etc.) can be easily and efficiently evaluated. The present invention can be used to make quantitative and qualitative determination(s) regarding the type and level of synergy between the BACs. In another example, the activity of BACs that inhibit enzymatic activity involved in biosynthesis of an amino acid such as isoleucine (e.g., sulfometuron methyl) may be observed (i.e., expected to be toxic) on minimal medium phenotypes, and the effect specifically reversed in phenotype media containing branch chain amino acids. The present invention also finds use in determinations of the type and number of BAC targets present in cells. Such determinations are significant, in that preferred BACs have specific modes of action and no side effects. Each potential new BAC must satisfy a number of criteria prior to its approval for use. The choice of a target is an important early step in the development of new BACs. In general, a target should provide adequate selectivity and spectrum (i.e., an antimicrobial will be highly specific and/or highly selective against the microbe with respect to the human host, and also be active against the desired pathogen spectrum); a target should be essential for the growth or viability of pathogens (i.e., at least under conditions of infection); and the function of the target should be known, so that assays and high throughput screens, such as those of the present invention can be utilized. The present invention also provides means to determine and assess the selectivity and spectrum of BACs, as well as the functionality, and degree of importance of various targets. In some embodiments of the present invention, the activity of the BAC is determined in such a manner that side effects, such as an interaction with multiple targets, are observed. For example, in one test BAC 1 is a specific drug that inhibits one target, protein 1. This is distinguished from BAC 2, which is found to be a non-specific drug, that inhibits protein 1, as well as protein 5. In the case where inhibition of protein 5 would be deleterious, this BAC would be determined to be unsuitable for use. Figure 1 provides a simplified schematic of one embodiment of the present invention designed to measure the effects of BACs on cells, using PMs. In this Figure and in Figure 2, the "phe" designations indicate phenotypes of the cells (e.g., the growth and/or respiration of the cells in a particular well of the phenotype microarray). At the top left, Figures 1 and 2 show a normal cell and a mutant cell (e.g., a gene knockout) which lacks the functional activity of a normally encoded protein, which in this example, is a potential drug target. In Figures 1 and 2, "gl" indicates the gene that codes for protein "pi," which is the potential drug target. Most drugs work by blocking the activity of a protein, so when a drug is added, the cell now lacks the function of the target protein. Thus, in either case (i.e., the mutant cell or a normal cell exposed to a drug), the cell lacks the function of the target protein (e.g., pi). The major difference between these cells is that in the case of the mutant cell the protein function was eliminated by genetic means, whereas in the case of the normal cell exposed to the drug, the protein function was eliminated by chemical means. In Figure 1 , drug 1 is a good candidate for inactivating its target protein (pi), because it is active and specific (i.e., it only effects phenotype 1). In contrast, drug 2 is a poor candidate because it inactivates another protein, designated as protein 5 (p5), as well as pi (i.e., it affects both phenotypes 1 and 5). Because drug 2 has non-specific effects on the cell, drug 2 is likely to cause side effects and be a less desirable compound to use in treatment regimens. Thus, in some embodiments of the present invention, the activity of the BAC is determined in such a manner that side effects, such as an interaction with multiple targets, are observed. For example, in one test BAC 1 is a specific drug that inhibits one target, protein 1. This is distinguished from BAC 2, which is found to be a non-specific drug, that inhibits protein 1, as well as protein 5. In the case where inhibition of protein 5 would be deleterious, this BAC would be determined to be unsuitable for use. Figure 2 provides a simplified schematic of how PMs can detect drug interactions. When a cell is simultaneously exposed to "drug 1" and "drug 2," the consequent effect is more than just the effect of drug 1 (i.e., phe 1 changed) and drug 2 (i.e., phe 5 changed), as phe 6 and phe 7 were also changed. This demonstrates an extra effect of the drugs that cannot be predicted based on the known effects of the drugs used singly. These extra effects (i.e., changes on phe 6 and phe 7) may be beneficial (i.e., synergistic) or they may be harmful (i.e., antagonistic). As shown schematically in Figure 3, during the testing process, the cells in various wells are placed under different environmental stresses. These stresses pressure the organisms to adapt in order to survive. For example, in some wells, the cells may be partially starved for an element such as phosphorus, while in other wells the cells may be adapting to high salt conditions, undergoing DNA repair, growing at low pH, producing partially defective cell walls, or experiencing decreased ribosome function. Thus, the present invention provides means, starting from a single culture (or cell population), to expose that culture to various environmental conditions, and thereby create an array of cells in different physiological states. If an antimicrobial drug or other BAC is also added to the culture, the present invention provides means to simultaneously observe the effect of the BAC on the culture under many environmental and physiological conditions. This is very different and much more powerful than current practice for such tasks as determining the antimicrobial susceptibility patterns of organisms, which typically grow the culture only under one condition that provides for rapid growth of the organism (i.e., optimal growth conditions). In traditional and current methods for antimicrobial susceptibility testing, every effort is made to standardize the procedure and its interpretation. Although the methods are relatively simple (e.g., Kirby-Bauer disk diffusion and tube dilution methods), they are strictly controlled in the clinical setting by the National Committee for Clinical Laboratory Standards (NCCLS) (See, Hindler, "Antimicrobial Susceptibility Testing," in Isenberg (ed.), Clinical Microbiology Procedures Handbook, vol. 1, American Society for Microbiology, Washington, D.C., [1994], pages 5.0.1 through 5.25.1). Indeed, the practitioner is warned to not deviate from the standard methods or misleading results may be obtained. However, although antimicrobial susceptibility tests are one of the most important tasks of the clinical microbiology laboratory, it is recognized that these tests simply provide an in vitro prediction of how well a particular antimicrobial will work to treat a patient's disease (See, Jorgensen and Sahm, "Antimicrobial Susceptibility Testing: General Considerations, in Murray et al, (eds.) Manual of Clinical Microbioloev. 6th edition, American Society for Microbiology, Washington, D.C. [1995], pages 1277- 1280). Because the approved testing procedures are highly standardized, there is no mechanism for testing the susceptibility of organisms under different environmental stresses. This is in direct contrast to the present invention, which allows the determination of antimicrobial susceptibility (as well as the determination of other characteristics of a particular culture) under multiple and widely different conditions, such as those that the organisms may encounter in vivo. Thus, as indicated above, the present invention further finds use in the determination of synergy and antagonism. As is known in the art, it is important to know which BAC combinations are synergistic and which are antagonistic or harmful when utilized. The present invention provides methods and compositions for determining these relationships. The results obtained using the present invention can produce simple or complex patterns which may be recorded quantitatively and analyzed using standard methods known in the art. In particular, multidimenstional pattern analysis methods, including but not limited to non-metric multidimensional scaling (NMDS), principle component and canonical variate analysis, heuristic clustering analysis, distance and similarity matrix generation, data extraction and mining activities, and bioinformatics tools and practices. In methods such as ANOVA, sample sets are compared based on how closely they have the same degree of variability. ANCOVA provides information about the joint variability of data sets. It is also contemplated that principle component analysis (PCA) and canonical variate analysis (CVA) will find use in the present invention. PCA provides an algebraic analysis of the data matrix, while CVA is applied to the distance or similarity matrix associated with the same algebraic analysis of the data. Correspondence analysis and discriminate analysis provide methods to use the basic PCA algorithm. As with CVA, the difference is how the data are handled prior to application of the algorithm. Monte Carlo permutation tests are also contemplated for use in conjunction with the present invention. These tests provide an indication of the stability and reliability of cluster analysis results. In addition, it is contemplated that use of the Gini coefficient will be used in analyzing data obtained using the present invention (See e.g., Harch et al, J. Microbiol. Meth., 30:91-101 [1997]). For example, in this analysis, the Gini coefficient can be used as a measure to quantify unequal use of certain substrates or BACs. However, the choice of statistical methods will depend upon the use of the present invention. Thus, it is not intended that the present invention be limited to any particular method for data analysis. Indeed, it is contemplated that methods such as the Shannon index, as well as other suitable approaches will be used to analyze data generated using the present invention (See also, Garland, FEMS Microbiol. Ecol., 24:289-300 [1997]). In addition, the present invention provides methods for determining data on BAC susceptibility profiles and permitting their easy storage in a database. In preferred embodiments, the present invention is suitable for the comparative phenotype testing of microorganisms as well as other cells. In one preferred method, the present invention encompasses methods and compositions for the phenotypic testing of E. coli and S. cerevisiae, which are important prokaryotic and eukaryotic "model" organisms for many biological systems. However, it is not intended that the present invention be limited to these organisms. Indeed, it is contemplated that the present invention will find use in analyzing organisms of medical, veterinary, industrial, and environmental importance and/or interest. It is not intended that the invention be limited to a particular genus, species nor group of organisms or cells. In addition to commonly isolated organisms, the range of cell types that can be tested using the methods and compositions of the present invention includes cells that undergo complex forms of differentiation, filamentation, sporulation, etc. Indeed, it is also intended that the present invention will find use with cells of any type, including, but not limited to cells maintained in cell culture, cell lines, etc., including mammalian, insect, and plant cells. The compositions and methods of the present invention are particularly targeted toward some of the most economically important organisms, as well as species of clinical importance. As various cells may be characterized using the PMs of the present invention, it is not intended that the choice of primary isolation or culture media be limited to particular formulae. As indicated above, the present invention finds use with prokaryotic (e.g., bacteria) cells, as well as eukaryotic cells. For example, the present invention finds use with cells obtained from various animal and other eukaryotic species. For example, the present invention finds use with mammalian, insect, avian, piscine, reptilian, and amphibian cells. Thus, mammalian cells, including but not limited to human and non- human animal cells, including cells from laboratory, domestic and livestock animals (e.g., canines, felines, equines, bovines, porcines, caprines, ovines, avians [e.g., chickens, turkeys, ostriches, etc.], lagomorphs [e.g., rabbits and hares], rodents [e.g., rats, mice, hamsters, guinea pigs, etc.], and non-human primates), as well as cells obtained from zoo, feral, and wild animals find use with the present invention. Thus, the present invention finds use with any number of vertebrate, as well as invertebrate animals. Examples of invertebrate cells that find use with the present invention include, but are not limited to insects such as fruit flies, cockroaches, mosquitoes, beetles, moths, butterflies, and worms (e.g., C. elegans). Indeed, it is not intended that the present invention be limited to cells from any particular species. As cell culture methods and techniques for cells from various classes of animals (e.g., mammals, reptiles, amphibians, and insects) are well-known to those in the art, those in the art recognize that the present invention is suitable for use with cells from any animal source. In addition to animal cells, the present invention finds use with other eukaryotic cells, including but not limited to fungal cells. For example, the present invention finds use with yeasts (e.g., Candida, Cryptococcus, Saccharomyces, Schizosaccharomyces, Torulopsis, and Rhodotorula) and molds (e.g., Aspergillus, Alternaria, Coccidioides, Histoplasma, Blastomyces, Paracoccidiodes, Penicillium, Fusaήum, etc.). Thus, the present invention encompasses use with dimorphic fungi, as well as fungal species with only one form (i.e., mold or yeast). In addition to animal cells, the present invention finds use with cells obtained from plants, including but not limited to rice, tobacco, maize, arabidopsis. Indeed, the present invention finds use with agriculturally useful (e.g., crops for food and feed), as well as horticulturally (e.g., decorative plants and flowers) useful plants, and wild plants. It is not intended that the present invention be limited to any particular plant or type of plant. In addition, various plant cells (e.g., root, stem, leaf, flower, etc.) find use with the present invention. In addition, the present invention finds use with cells from various organs and tissues (e.g., skin, respiratory system, digestive system, urinary tract, reproductive tract, circulatory system, skeletal system, sensory system [e.g., sight, smell, taste, etc.], muscle, and connective tissue). In addition, the present invention finds use with various embryological cell types and cells in various stages of development (e.g., stem cells, oocytes, zygotes, blastocoeles, fibroblasts, etc.). Thus, it is not intended that the present invention be limited to cells of any particular type. Indeed, as cell culture methods and techniques for cells from various organs, tissues, and bodily systems, (e.g., mammals, reptiles, amphibians, and insects) are well-known to those in the art, those in the art recognize that the present invention is suitable for use with cells from any source. The present invention finds use with normal eukaryotic and prokaryotic cells, as well as abnormal cells, (e.g., cancer cells, cells undergoing apoptosis, mutant cells, pre- cancerous cells, diseased cells, etc.). Cells that have been infected with a pathogenic or other organism (e.g,. viruses, bacteria, mycoplasmas, parasites, fungi, etc.), also find use with the present invention. Thus, it is not intended that the present invention be limited to cells in any particular stage of development (e.g., fetal, adult, senescent cells, etc.) or health. Mutant cells such as those that naturally occur, as well as genetically engineered cells (e.g., knock-outs, knock-ins), plasmid-containing cells, transfected cells, transformed cells, chemically-induced mutant cells, radiation-induced mutant cells, etc., also find use with the present invention. The following Table lists a few in vitro tumor cell lines that find use with the present invention. However, it is not intended that the present invention be limited to the few cell lines listed herein. The present invention further finds use with cultured cells, including but not limited to primary cultured cells, cell lines, cell strains, and other cells maintained in cell cultures. Numerous cell lines and strains are available from depositories such as the American Type Culture Collection (ATCC). For example, cell lines such as HeLa, Vero, MDCK, A-9, HFF, CHO, MRC-5, HeP-2, CV-1, BGMK, BHK, BHK-21, A549, MvlLu, HEK-293, HT-29, MCF-7, AC- 133, CD-4, C3A, hTERT-RPEl, KB, 3T3, Jurkat, IMR- 90, F9, PCI 3, LNCaP, PC-3, US7, HUH-7, NCI-460, NCI-H23, MB-MDA-237, HME, MKN45, CD80-AT, A2780, OVCAR-3, SK-OV-3, NBS-1LB, MCF-10, Rat-1, RTS34St, etc., as well as McCoy and other cells maintained in culture systems. In addition, the present invention finds use with cells with selectable markers (i.e., the use of a gene which encodes an enzymatic activity that confers resistance to an antibiotic or drug upon the cell in which the selectable marker is expressed). Selectable markers may be "dominant"; a dominant selectable marker encodes an enzymatic activity which can be detected in any mammalian cell line. Examples of dominant selectable markers include the aminoglycoside 3' phosphotransferase gene (also referred to as the neo gene) which confers resistance to the drug G418 in mammalian cells, the hygromycin G phosphotransferase (hyg) gene which confers resistance to the antibiotic hygromycin, the bacterial xanthine-guanine phosphoribosyl transferase gene (also referred to as the gpt gene) which confers the ability to grow in the presence of mycophenolic acid, and the chloramphenicol acetyl transferase gene (also referred to as the cat gene) which confers resistance to chloramphenicol acetyl transferase. Other selectable markers are not dominant in that their use must be in conjunction with a cell line that lacks the relevant enzyme activity. Examples of non-dominant selectable markers include the thymidine kinase (tk) gene which is used in conjunction with tk ~ cell lines, the cad gene (i.e., encoding the CAD protein, which possesses the first three enzymatic activities of de novo uridine biosynthesis) which is used in conjunction with CAD-deficient cells (i.e., UrdA mutants), and the mammalian hypoxanthine-guanine phosphoribosyl transferase (hprt) gene which is used in conjunction with hprt " cell lines. A review of the use of selectable markers in mammalian cell lines is provided in Sambrook et al, (Sambrook et al, Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, New York [1989], at pp.16.9- 16.15.) The present invention contemplates using a multiwell testing device essentially similar in structure to microtiter plates ("microplates" or "MicroPlates™" microtiter plates) which are commonly used in the art and commercially available from numerous scientific supply sources (e.g., Biolog, Fisher, etc.). It is also intended that the present invention encompasses various testing formats. Thus, in addition to standard microtiter plate testing methods, it is contemplated that the present invention be used with various gelling agents, including but not limited to alginate, carrageenan, and gellan gum (e.g., Gelrite™ and/or Phytagel™), as described in U.S. Patent Nos. 5,627,045, and 5,882,882, and 5,989,853, as well as the MicroCard™ miniaturized testing plates described in U.S. Patent Nos. 5,589,350 and 5,800,785, all of which are herein incorporated by reference. Thus, in one embodiment, a microplate (e.g., a MicroPlate™ microtiter plate) format is used. In this embodiment, the gel-forming matrix containing suspended cells is used to inoculate the wells of a MicroPlate™, MicroCard™ or another receptacle. At the time of inoculation, the gel-forming matrix is in liquid form, allowing for easy dispensing of the suspension into the compartments. These compartments contain dried biochemicals and cations. Upon contact of the gel-forming matrix with the cations, the suspension solidifies to form a soft gel, with the cells evenly distributed throughout. This gel is sufficiently viscous or rigid that to keep the cells suspended so that they do not sink to the bottom of the wells or testing array. In another embodiment, a MicroCard ™ miniaturized testing format is used. One embodiment of the device of the present invention comprises a housing with a liquid entry port through which the sample is introduced. The housing further contains a channel providing communication to a testing region so that a liquid can flow into a plurality of wells or compartments. The channel is enclosed by the surface of a hydrophobic, gas-venting membrane adapted for forming one surface of the wells and attached to one side of the housing. The housing can be sealed on its other side by a solid base. In other embodiments, a flexible tape may be substituted for the solid base or the solid base may be molded so as to be integral with the housing. After filling the device with the solution or gel-forming matrix containing cells, an optional non-venting material such as tape (e.g., polyester tape) can be adhered to the outer surface of the gas- venting membrane to seal it against evaporation of the gel matrix within the device through the gas-venting membrane. At the time of delivery, the gel- forming matrix with suspended cells is in liquid form. Once the liquid comes into contact with gel-initiating compounds present in the testing region, a gel matrix is produced, trapping the suspended cells. The present invention is particularly well-suited for use as a kit. In particular, this invention in the form of a kit, is suitable for the easy and rapid phenotypic testing of various cells, including commonly isolated bacteria, as well as actinomycetes and fungi (i.e., yeasts and molds), in addition to mammalian, insect, and plant cells. In particular, the present invention provides compositions and methods for the phenotypic analysis of cells, in particular, their susceptibility and resistance to various compounds with potential BAC activity. While it is contemplated that the PMs of the present invention will be interpreted visually, it is also contemplated that instruments will find use in reading and interpreting the results of the assays. For example, a practical, efficient and cost-effective system for reading testing panels is described in U.S. Patent Application Serial No. 09/277,353, which is hereby incorporated by reference. This instrument facilitates the direct and simultaneous analysis of cells and cell lines for thousands of phenotypes. The present invention provides methods and compositions for the phenotypic analysis of prokaryotic, as well as eukaryotic cells. Indeed, the present invention is not limited to any particular organism, cell, or testing format. In many embodiments, the present invention provides one or more testing panels, with each test panel including substrates for 95 phenotypic tests. In particular, the present invention allows testing of numerous BAC compounds. However, it is not intended that the present invention be limited to a particular number of tests. For example, some panels are currently available that allow 384 or 1536 substrates to be tested in one array. Thus, the present invention allows testing of numerous BAC compounds. However, it is not intended that the present invention be limited solely to the testing of single BAC compounds. Thus, it is intended that the present invention encompasses testing panels with test substrates of any type suitable for the phenotypic testing of various cells. Indeed, it is contemplated that combinations of substrates will be used in the methods of the present invention, including individual BACs, potential BACs, combinations of BACs, and BACs tested in conjunction with other substrates (e.g., carbon or nitrogen sources). Definitions The terms "sample" and "specimen" in the present specification and claims are used in their broadest sense. On the one hand, they are meant to include a specimen or culture. On the other hand, they are meant to include both biological and environmental samples. These terms encompasses all types of samples obtained from humans and other animals, including but not limited to, body fluids such as urine, blood, fecal matter, cerebrospinal fluid (CSF), semen, and saliva, as well as solid tissue. These terms also refers to swabs and other sampling devices which are commonly used to obtain samples for culture of microorganisms. Biological samples may be animal, including human, fluid or tissue, food products and ingredients such as dairy items, vegetables, meat and meat by-products, and waste. Environmental samples include environmental material such as surface matter, soil, water, and industrial samples, as well as samples obtained from food and dairy processing instruments, apparatus, equipment, disposable, and non-disposable items. These examples are not to be construed as limiting the sample types applicable to the present invention. Whether biological or environmental, a sample suspected of containing microorganisms may (or may not) first be subjected to an enrichment means to create a "pure culture" of microorganisms. By "enrichment means" or "enrichment treatment," the present invention contemplates (i) conventional techniques for isolating a particular microorganism of interest away from other microorganisms by means of liquid, solid, semi-solid or any other culture medium and/or technique, and (ii) novel techniques for isolating particular microorganisms away from other microorganisms. It is not intended that the present invention be limited only to one enrichment step or type of enrichment means. For example, it is within the scope of the present invention, following subjecting a sample to a conventional enrichment means, to subject the resultant preparation to further purification such that a pure culture of a strain of a species of interest is produced. This pure culture may then be analyzed by the medium and method of the present invention. As used herein, the term "primary isolation" refers to the process of culturing organisms directly from a sample. Thus, primary isolation involves such processes as inoculating an agar plate from a culture swab, urine sample, environmental sample, etc. Primary isolation may be accomplished using solid or semi-solid agar media, or in liquid. As used herein, the term "isolation" refers to any cultivation of organisms, whether it be primary isolation or any subsequent cultivation, including "passage" or "transfer" of stock cultures of organisms for maintenance and/or use. As used herein, the term "culture" refers to any sample or specimen which is suspected of containing one or more microorganisms or cells. In particularly preferred embodiments, the term is used in reference to bacteria and fungi. "Pure cultures" are cultures in which the organisms present are only of one strain of a particular genus and species. This is in contrast to "mixed cultures," which are cultures in which more than one genus and/or species of microorganism are present. As used herein, the term "eukaryote" refers to cells or organisms that have a unit membrane-bound (t.e., true) nucleus and usually have other organelles. Most eukaryotes have DNA that is complexed with histones and present in several chromosomes. The eukaryotes include algae, fungi, protozoa, plants, and animals. It is not intended that the present invention be limited to any particular eukaryotic cell or organism. Indeed, it is intended that the term encompass any organism or cell that has the characteristics typically associated with eukaryotic cells (See e.g., Brock et al, (eds), Biology of Microorganisms. 7th ed., Prentice Hall, New Jersey [1994], at pages 86-87). As used herein, the term "prokaryote" refers to organisms or cells that lack a unit membrane-bound (i.e., true) nucleus and other organelles (e.g., there is no nucleolus), and typically have a genome comprised of a single circular DNA. In most cases, cell walls are present. The prokaryotes include bacteria (i.e., eubacteria) and archaea (i.e., archaebacteria). It is not intended that the present invention be limited to any particular prokaryotic cell or organism. Indeed, it is intended that the term encompass any organism or cell that has the characteristics typically associated with prokaryotic cells (See e.g., Brock et al, (eds), Biology of Microorganisms, 7th ed., Prentice Hall, New Jersey [1994], at pages 86-87). As used herein, the term "organism" is used to refer to any species or type of microorganism, including but not limited to bacteria, yeasts and other fungi. As used herein, the term fungi, is used in reference to eukaryotic organisms such as the molds and yeasts, including dimorphic fungi. As used herein, the term "spore" refers to any form of reproductive elements produced asexually (e.g., conidia) or sexually by such organisms as bacteria, fungi, algae, protozoa, etc. It is also used in reference to structures within microorganisms such as members of the genus Bacillus, which provide advantages to the individual cells in terms of survival under harsh environmental conditions. It is not intended that the term be limited to any particular type or location of spores, such as "endospores" or "exospores." Rather, the term is used in the very broadest sense. As used herein, the terms "microbiological media" and "microbiological culture media," and "media" refer to any substrate for the growth and reproduction of microorganisms. "Media" may be used in reference to solid plated media which support the growth of microorganisms. Also included within this definition are semi-solid and liquid microbial growth systems including those that incorporate living host organisms, as well as any type of media. As used herein, the terms "culture media," and "cell culture media," refers to media that are suitable to support the growth of cells in vitro (i.e., cell cultures). It is not intended that the term be limited to any particular cell culture medium. For example, it is intended that the definition encompass outgrowth as well as maintenance media. Indeed, it is intended that the term encompass any culture medium suitable for the growth of the cell cultures of interest. As used herein, the term "defined medium" refers to a medium in which the components are known. For example, the term encompasses synthetic media prepared using particular ingredients of known composition. However, it is not intended that the present invention be limited to any particular medium or type of medium. In addition, the present invention encompasses defined media with additional uncharacterized components (i.e., the defined medium is the basal medium to which various compounds are added). In contrast to defined media, "undefined media" are media that contain uncharacterized or unknown constituents (e.g., trypticase soy broth, yeast extract, serum, plasma, etc.). As used herein, the terms "monolayer," "monolayer culture," and "monolayer cell culture," refer to cells that have adhered to a substrate and grow in as a layer that is one eel) in thickness. Monolayers may be grown in any format, including but not limited to flasks, tubes, coverslips (e.g., shell vials), roller bottles, etc. Cells may also be grown attached to microcarriers, including but not limited to beads. As used herein, the term "confluent" refers to adherent cells that are in contact with each other, such that there is no substrate that is uncovered by cells. As used herein, the term "adherent" refers to cells that are "anchorage-dependent" (i.e., require attachment to a solid substrate or surface for survival and/or growth), and are attached to a solid substrate. In contrast, "anchorage-independent" cells do not require attachment to a solid substrate or survival for survival and/or growth. As used herein, the term "contact inhibition" refers to the inhibition of cell membrane ruffling and cell motility when cells are in complete contact with other adjacent cells (e.g., in a confluent culture). This stage often precedes cessation of cell proliferation, but the two are not necessarily causally related. As used herein, the term "suspension," and "suspension culture," refers to cells that survive and proliferate without being attached to a substrate. Suspension cultures are typically produced using hematopoietic cells, transformed cell lines, and cells from malignant tumors. As used herein, the term "microcarrier beads" refer to beads that are suitable for cell attachment and growth. These beads are commercially available and are commonly used for the growth and maintenance of cells in culture. In particularly preferred embodiments, cells are grown attached to beads placed in liquid growth medium. Thus, in some embodiments, cells are grown in suspension but are attached to microcarrier beads. As used herein, the term "cell type," refers to any cell, regardless of its source or characteristics. As used herein, the term "cell line," refers to cells that are cultured in vitro, including primary cell lines, finite cell lines, continuous cell lines, and transformed cell lines. As used herein, the terms "primary cell culture," and "primary culture," refer to cell cultures that have been directly obtained from animal, plant or insect tissue. These cultures may be derived from adults as well as fetal tissue. As used herein, the term "finite cell lines," refer to cell cultures that are capable of a limited number of population doublings prior to senescence. As used herein, the term "continuous cell lines," refer to cell cultures that have an indefinite lifespan. Some cell lines arise from spontaneous transformation, while others are engineered (e.g., by telomerization). In many cases, the cells have undergone a "crisis" phase during which a population of cells in a primary or finite cell line apparently ceases to grow, but yet a population of cells emerges with the general characteristics of a reduced cell size, higher growth rate, higher cloning efficiency, increased tumorigenicity, and a variable chromosomal complement. These cells often result from spontaneous transformation in vitro. These cells have an indefinite lifespan. As used herein, the term "transformed cell lines," refers to cell cultures that have been transformed into continuous cell lines with the characteristics as described above. Transformed cell lines can be derived directly from tumor tissue and also by in vitro transformation of cells with whole virus (e.g., SV40 or EBV), or DNA fragments derived from a transforming virus using vector systems. As used herein, the term "mixed cell culture," refers to a mixture of two types of cells. In some embodiments, the cells are cell lines that are not genetically engineered, while in other preferred embodiments the cells are genetically engineered cell lines. As used herein, the term "auxotroph" is used in reference to an organism or cell line that can be grown only in the presence of nutritional supplements (e.g., growth factors). Thus, in auxotrophic testing, auxotrophs will only grow in the presence of the supplement(s) that is/are necessary for their growth, and will not grow in media that lack the necessary supplement(s). As used herein, the term "carbon source" is used in reference to any compound which may be utilized as a source of carbon for cell growth and/or metabolism. Carbon sources may be in various forms, including, but not limited to polymers, carbohydrates, acids, alcohols, aldehydes, ketones, amino acids, and peptides. As used herein, the term "nitrogen source" is used in reference to any compound which may be utilized as a source of nitrogen for cell growth and/or metabolism. As with carbon sources, nitrogen sources may be in various forms, such as free nitrogen, as well as compounds which contain nitrogen, including but not limited to amino acids, peptones, vitamins, and nitrogenous salts. As used herein, the term "phosphorus source" is used in reference to any compound which may be utilized as a source of phosphorus for cell growth and/or metabolism. As with sources of other elements (e.g., carbon and nitrogen), phosphorus sources may be in various forms, such as free phosphorus, as well as compounds which contain phosphorus. As used herein, the term "sulfur source" is used in reference to any compound which may be utilized as a source of sulfur for cell growth and/or metabolism. As with carbon, nitrogen and phosphorus sources, sulfur sources may be in various forms, such as free sulfur, as well as compounds which contain sulfur. As used herein, the term "growth stimulating nutrients" is used in reference to any compounds that enhance the growth of an organism. It is not intended that the present invention be limited to any particular growth stimulating nutrients, although in particularly preferred embodiments, the present invention contemplates the use of growth factors, amino acids, nucleic acid precursors, lipids, cell membrane and wall precursors, vitamins, hormones, minerals, as well as other elements and compounds that stimulate growth of cells. As used herein, the term "drug" refers to any compound that has biological activity. In some embodiments, the term is used in reference to antimicrobials, although it is not intended that the term be limited to antimicrobials. Indeed, the term encompasses compounds that alter cell proliferation, metabolism, and or growth, as well as compounds that affect microbial and/or other cells (e.g., animal cells). Thus, the term encompasses such compounds as anti-inflammatories, anti-histaminics, emetics, anti- emetics, and other compounds that cause some effect in biological systems and/or cells. As used herein, the term "antimicrobial" is used in reference to any compound which inhibits the growth of, or kills microorganisms. It is intended that the term be used in its broadest sense, and includes, but is not limited to compounds such as antibiotics which are produced naturally or synthetically. It is also intended that the term includes any other organic and inorganic compounds that are useful for inhibiting the growth of, or killing microorganisms. As used herein, the term "testing substrate" is used in reference to any nutrient source (e.g., carbon, nitrogen, phosphorus, and sulfur sources, as well as growth stimulating nutrients, antimicrobials, and chromogenic substrates) that may be utilized to differentiate bacteria based on biochemical characteristics. For example, one cell species may utilize one testing substrate that is not utilized by another species. This utilization may then be used to differentiate between these two species. It is contemplated that numerous testing substrates be utilized in combination. Testing substrates may be tested individually (e.g., one substrate per testing well or compartment, or testing area) or in combination (e.g., multiple testing substrates mixed together and provided as a "cocktail"). As used herein, the term "BAC" is used in reference to any compound that has an effect on a cell. The effect can be to stimulate or inhibit cell growth or respiration, to bind to any cellular component, to influence the activity of any function or protein- catalyzed activity of a cell. Thus, it is not intended that the present invention be limited to any compound or class of compounds. Indeed, the BACs of the present invention include any compound that has any effect on a particular cell. Following exposure to a testing substrate (e.g., BAC(s), carbon or nitrogen sources, etc.), the response of an organism or cell line may be detected. This detection may be visual (i.e., by eye) or accomplished with the assistance of machine(s) (e.g., the Biolog MicroStation Reader™). For example, the response of organisms to carbon sources may be detected as turbidity in the suspension due to the utilization of the testing substrate by the organisms. Likewise, growth can be used as an indicator that an organism is not inhibited by certain BACs. In one embodiment, color is used to indicate the presence or absence of organism growth/metabolism. As used herein, the term "colorimetric indicator" refers to any compound that is used to indicate by means of a color change that a reaction has occurred or that a cell or organism is capable of metabolizing a particular compound. This includes, but is not limited to any color, as used in the traditional sense of "colors," such as indigo, blue, red, yellow, green, orange, brown, etc., as well as fluorochromic or fluorogenic compounds, which produce colors detectable with fluorescence (e.g., the yellow-green of fluorescein, the red of rhodamine, etc.). It is intended that such other indicators as dyes (e.g., pH and redox) and luminogenic compounds be encompassed within this definition. In preferred embodiments, the colorimetric indicators of the present invention include, but are not limited to chromogenic substrates, oxidation-reduction indicators, and pH indicators. In some particularly preferred embodiments, the oxidation-reduction indicator is tetrazolium violet, while in other embodiments, the oxidation-reduction indicator is redox purple. The colorimetric indicator can be monitored visually or by means of a device or machine (e.g., a colorimeter, photometer or camera). As used herein, the terms "chromogenic compound" and "chromogenic substrate," refer to any compound useful in detection systems by their light absorption or emission characteristics. The term is intended to encompass any enzymatic cleavage products, soluble, as well as insoluble, which are detectable either visually or with optical machinery. Included within the designation "chromogenic" are all enzymatic substrates which produce an end product which is detectable as a color change. This includes, but is not limited to any color, as used in the traditional sense of "colors," such as indigo, blue, red, yellow, green, orange, brown, etc., as well as fluorochromic or fluorogenic compounds, which produce colors detectable with fluorescence (e.g., the yellow-green of fluorescein, the red of rhodamine, etc.). It is intended that such other indicators as dyes (e.g., pH and redox) and luminogenic compounds be encompassed within this definition. As used herein, the commonly used meaning of the terms "pH indicator," "redox indicator," and "oxidation- reduction indicator," are intended. Thus, "pH indicator" encompasses all compounds commonly used for detection of pH changes, including, but not limited to phenol red, neutral red, bromthymol blue, bromcresol purple, bromcresol green, bromchlorophenol blue, m-cresol purple, thymol blue, bromcresol purple, xylenol blue, methyl red, methyl orange, and cresol red. The terms "redox indicator" and "oxidation-reduction indicator" encompass all compounds commonly used for detection of oxidation/reduction potentials (i.e., "eH") including, but not limited to various types or forms of tetrazolium, resazurin, methylene blue, and quinone-imide redox dyes including the compounds known as "methyl purple" and derivatives of methyl purple. The quinone-imide redox dye known as methyl purple is referred to herein as "redox purple" (See e.g., U.S. Patent No. 5,882,882, herein incorporated by reference). In a particularly preferred embodiment, "redox purple" comprises the compound with the chemical structure shown in Figure 5, VI of U.S. Patent No. 5,882,882. It is contemplated that analogous derivatives of the reagent (e.g., alkali salts, alkyl O-esters), with modified properties (e.g., solubility, cell permeability, toxicity, and/or modified color(s)/absorption wavelengths) will be produced using slight modifications of the methods described in the accompanying Examples. It is also contemplated that various forms of "redox purple" (e.g., salts, etc.), may be effectively used in combination as a redox indicator in the present invention. As used herein, the terms "testing means" and "testing device" are used in reference to testing systems in which at least one organism is tested for at least one characteristic, such as utilization of a particular carbon source, nitrogen source, or chromogenic substrate, and/or susceptibility to a BAC agent. This definition is intended to encompass any suitable means to contain a reaction mixture, suspension, or test. It is intended that the term encompass microplates, petri plates, microcard devices, or any other supporting structure that is suitable for use. For example, a microplate having at least one gel-initiating agent included in each of a plurality of wells or compartments, comprises a testing means. Other examples of testing means include microplates without gel-initiating means included in the well. It is also intended that other compounds such as carbon sources or BACs will be included within the compartments. The definition encompasses the MicroPlate™ microtiter plates for characterization of microorganisms (available from Biolog). The definition is also intended to encompass a "microcard" or miniaturized plates or cards which are similar in function, but much smaller than standard microtiter plates (for example, many testing devices can be conveniently held in a user's hand). In particularly preferred embodiments, the microcards are the MicroCard™ device described in U.S. Patent Nos. 5,589,350, and 5,800,785, both of which are herein incorporated by reference (available from Biolog). It is not intended that the present invention be limited to a particular size or configuration of testing device or testing means. For example, it is contemplated that various formats will be used with the present invention, including, but not limited to microtiter plates (including but not limited to MicroPlates™), miniaturized testing plates (e.g., MicroCard™ miniaturized testing cards), petri plates, petri plates with internal dividers used to separate different media placed within the plate, test tubes, as well as many other formats. As used herein, the term "gelling agent" is used in a broad generic sense, and includes compounds that are obtained from natural sources, as well as those that are prepared synthetically. As used herein, the term refers to any substance which becomes at least partially solidified when certain conditions are met. For example, one gelling agent encompassed within this definition is Gelrite™, a gellan which forms a gel upon exposure to divalent cations (e.g., Mg 2+ or Ca 2+ ); Gelrite™ is a gellan gum, produced by deacetylating a natural polysaccharide produced by Pseudomonas elodea, and is described by Kang et al. (U.S. Patent Nos. 4,326,052 and 4,326,053, herein incorporated by reference). Included within the definition are various gelling agents obtained from natural sources, including protein-based as well as carbohydrate-based gelling agents. One example is bacteriological agar, a polysaccharide complex extracted from kelp. Also included within the definition are such compounds as gelatins (e.g., water-soluble mixtures of high molecular weight proteins obtained from collagen), pectin (e.g., polysaccharides obtained from plants), carrageenans and alginic acids (e.g., polysaccharides obtained from seaweed), and gums (e.g., mucilaginous excretions from some plants and bacteria). It is contemplated that various carrageenan preparations will be used in the present invention, with iota carrageenan comprising a preferred embodiment. It is also contemplated that gelling agents used in the present invention may be obtained commercially from a supply company, such as Difco, BBL, Oxoid, Marcor, Sigma, or any other source. It is not intended that the term "gelling agent" be limited to compounds which result in the formation of a hard gel substance. A spectrum is contemplated, ranging from merely a more thickened or viscous colloidal suspension to one that is a firm gel. It is also not intended that the present invention be limited to the time it takes for the suspension to gel. Importantly, it is intended that the present invention provides a gelling agent suitable for production of a matrix in which organisms may grow (i.e., a "gel matrix"). The gel matrix of the present invention is a colloidal-type suspension of organisms produced when organisms are mixed with an aqueous solution containing a gelling agent, and this suspension is exposed to a gel-initiating agent. It is intended that this colloidal- type gel suspension be a continuous matrix medium throughout which organisms may be evenly dispersed without settling out of the matrix due to the influence of gravity. The gel matrix supports the growth of organisms within, under, and on top of the gel suspension. As used herein the term "gel-initiating agent" refers to any compound or element which results in the formation of a gel matrix, following exposure of a gelling agent to certain conditions or reagents. It is intended that "gel-initiating agent" encompass such reagents as cations (e.g., Ca 2+ , Mg 2+ , and K + ). Until the gelling agent contacts at least one gel-initiating agent, any suspension containing the gelling agent remains "ungelled" (i.e., there is no thickening, increased viscosity, nor hardening of the suspension). After contact, the suspension will become more viscous and may or may not form a rigid gel (i.e., contact will produce "gelling"). As used herein, the term "inoculating suspension" or "inoculant" is used in reference to a suspension which may be inoculated with organisms to be tested. It is not intended that the term "inoculating suspension" be limited to a particular fluid or liquid substance. For example, inoculating suspensions may be comprised of water, saline, or an aqueous solution which includes at least one gelling agent. It is also contemplated that an inoculating suspension may include a component to which water, saline or any aqueous material is added. It is contemplated in one embodiment, that the component comprises at least one component useful for the intended microorganism. It is not intended that the present invention be limited to a particular component. As used herein, the term "kit" is used in reference to a combination of reagents and other materials. It is contemplated that the kit may include reagents such as BACs, carbon sources, nitrogen sources, chromogenic substrates, diluents and other aqueous solutions, as well as specialized microplates (e.g., GN, GP, ES, YT, SF-N, SF-P, and other MicroPlates™, obtained from Biolog), inoculants, miniaturized testing cards (e.g., MicroCards™), and plated agar media. The present invention contemplates other reagents useful for the growth, identification and or determination of the BAC susceptibility of microorganisms. For example, the kit may include reagents for detecting the growth of microorganisms following inoculation of kit components (e.g., tetrazolium or resazurin included in some embodiments of the present invention). It is not intended that the term "kit" be limited to a particular combination of reagents and/or other materials. Further, in contrast to methods and kits which involve inoculating organisms on or into a preformed matrix such as an agar surface or broth, the present invention involves inoculation of a testing plate in which the organisms are suspended within a gel-forming matrix. As used herein, the term "oocyte" refers to a female gamete cell and includes primary oocytes, secondary oocytes and mature, unfertilized ovum. An oocyte is a large cell having a large nucleus (i.e., the germinal vesicle) surrounded by ooplasm. The ooplasm contains non-nuclear cytoplasmic contents including mRNA, ribosomes, mitochondria, yolk proteins, etc. The membrane of the oocyte is referred to herein as the "plasma membrane." The term "pre-maturation oocyte" as used herein refers to a female gamete cell following the oogonia stage (i.e., mitotic proliferation has occurred) that is isolated from an ovary (e.g., by aspiration) but which has not been exposed to maturation medium in vitro. Those of skill in the art know that the process of aspiration causes oocytes to begin the maturation process but that completion of the maturation process (i.e., formation of a secondary oocyte which has extruded the first polar body) in vitro requires the exposure of the aspirated oocytes to maturation medium. Pre-maturation oocytes will generally be arrested at the first anaphase of meiosis. The term "pre-fertilization oocyte" as used herein refers to a female gamete cell such as a pre-maturation oocyte following exposure to maturation medium in vitro but prior to exposure to sperm (i.e., matured but not fertilized). The pre-fertilization oocyte has completed the first meiotic division, has released the first polar body and lacks a nuclear membrane (the nuclear membrane will not reform until fertilization occurs; after fertilization, the second meiotic division occurs along with the extrusion of the second polar body and the formation of the male and female pronuclei). Pre-fertilization oocytes may also be referred to as matured oocytes at metaphase II of the second meiosis. The terms "unfertilized egg" or "unfertilized oocyte" as used herein refers to any female gamete cell which has not been fertilized and these terms encompass both pre- maturation and pre-fertilization oocytes. Although embodiments have been described with some particularity, many modifications and variations of the preferred embodiment are possible without deviating from the invention. EXPERIMENTAL The following examples are provided in order to demonstrate and further illustrate certain preferred embodiments and aspects of the present invention and are not to be construed as limiting the scope thereof. In the experimental disclosure which follows, the following abbreviations apply: eq (equivalents); M (Molar); μM (micromolar); N (Normal); mol (moles); mmol (millimoles); μmol (micromoles); nmol (nanomoles); g (grams); mg (milligrams); μg (micrograms); ng (nanograms); 1 or L (liters); ml (milliliters); μl (microliters); cm (centimeters); mm (millimeters); μm (micrometers); nm (nanometers); °C (degrees Centigrade); TSA (trypticase soy agar); YME or YEME (Yeast extract-malt extract agar); Redigel (RCR Scientific, Goshen, IN); Gelrite™ (Merck and Co., Rahway, NJ); Remel, (Remel, Lenexa, KS); Oxoid (Oxoid, Basingstoke, England); BBL (Becton Dickinson Microbiology Systems, Cockeysville, MD); DIFCO (Difco Laboratories, Detroit, MI, now part of Becton-Dickinson); Acumedia (Acumedia, Baltimore, MD); U.S. Biochemical (U.S. Biochemical Corp., Cleveland, OH); Fisher (Fisher Scientific, Pittsburgh, PA); Sigma (Sigma Chemical Co., St. Louis, MO.); Biolog (Biolog, Inc., Hayward, CA); ATCC (American Type Culture Collection, Rockville, Maryland); NCYC (National Collection of Yeast Cultures, Norwich, England); NCCLS (National Committee for Clinical Laboratory Standards); and Molecular Devices (Molecular Devices, Mountain View, CA). The three-letter abbreviations conventionally used for amino acids (e.g., "ala" designates alanine or an alanine residue) are also used in some of the following Examples. EXAMPLE 1 BAC Testing of Bacteria In this Example, the susceptibility of E. coli (MG1655) was tested in the presence of vancomycin (10 μg/ml) or sulfamethoxazole (235 μg/ml) in microarrays containing various additional compounds. The microarrays were present in three Biolog™ sensitivity test panels, referred to as ESI, ES2 and ES3 MicroPlates™. The organisms were added to a sterile aqueous suspension containing 0.40% NaCl, 0.03% pluronic F68, 0.01%) phytagel, and 0.01% tetrazolium violet, to a cell density of 85%> transmittance (as measured using a Biolog™ turbidimeter). The BAC to be tested was added to the suspension just prior to inoculating the organisms (100 μl/well) into the wells of the microarrays. The wells of these ES MicroPlates™ contained a basal broth medium consisting of tryptone (2 g/L), yeast extract (1 g/L), and NaCl (1 g/L). In addition to one positive control well, the wells of the ESI plates contained the following antimicrobials (one compound at a particular concentration per well): acriflavine (4.0 μg/ml, 8.0 μg/ml, and 16 μg/ml), ampicillin (2.0 μg/ml, 4.0 μg/ml, 8.0 μg/ml, and 16 μg/ml), nafcillin (75 μg/ml, 150 μg/ml, 300 μg/ml, and 600 μg/ml,), lincomycin (50 μg/ml, 100 μg/ml, 200 μg/ml, and 400 μg/ml), chloramphenicol (0.1 μg/ml, 0.2 μg/ml, 0.4 μg/ml, and 0.8 μg/ml), chlortetracycline (0.125 μg/ml, 0.25 μg/ml, 0.50 μg/ml, and 1.0 μg/ml), tetracycline (0.033 μg/ml, 0.066 μg/ml, 0.133 μg/ml, and 0.266μg/ml), gentamycin (0.25 μg/ml, 0.50 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), kanamycin (0.25 μg/ml, 0.5 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), neomycin (0.75 μg/ml, 1.5 μg/ml, 3.0 μg/ml, and 6.0 μg/ml), vancomycin (10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml), bacitracin (208 μg/ml, 416 μg/ml, 833 μg/ml, and 1666 μg/ml), clindamycin (3.3 μg/ml, 6.6 μg/ml, 13.2 μg/ml, and 26.4 μg/ml), cloxacillin (100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml), erythromycin (2.5 μg/ml, 5.0 μg/ml, 10 μg/ml, and 20 μg/ml), penicillin G (5 μg/ml, 10 μg/ml, 20 μg/ml, and 40 μg/ml), novobiocin (33 μg/ml, 66 μg/ml, 133 μg/ml, and 266 μg/ml), spiramycin (5.0 μg/ml, 10 μg/ml, 20 μg/ml, and 40 μg/ml,), trimethoprim (0.17 μg/ml, 0.33 μg/ml, 0.67 μg/ml, and 1.3 μg/ml), streptomycin (0.38 μg/ml, 0.75 μg/ml, 1.5 μg/ml, and 3.0 μg/ml), cephaloridine (0.75 μg/ml, 1.5 μg/ml, 3.0 μg/ml, and 6.0 μg/ml), cefuroxime (0.5 μg/ml, 1.0 μg/ml, 2.0 μg/ml, and 4.0 μg/ml), roxithromycin (10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml), and piperacillin (0.5 μg/ml, 1.0 μg/ml, 2.0 μg/ml, and 4.0 μg/ml). The wells of the ES2 plates contained the following antimicrobials (one compound at a particular concentration per well): azomycin (0.2 μg/ml, 0.4 μg/ml, 0.8 μg/ml, and 1.6 μg/ml), rifampicin (0.25 μg/ml, 0.5 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), tylosin tartrate (25 μg/ml, 50 μg/ml, 100 μg/ml, and 200 μg/ml), cefazolin (0.5 μg/ml, 1.0 μg/ml, 2.0 μg/ml, and 4.0 μg/ml), cephalothin (2.5 μg/ml, 5.0 μg/ml, 10 μg/ml, and 20 μg/ml), cefaclor (0.66 μg/ml, 1.33 μg/ml„ 2.66 μg/ml, and 5.33 μg/ml), rifamycin SV (1.5 μg/ml, 3.0 μg/ml, 6.0 μg/ml, and 12 μg/ml), cefsulodin 4.0 μg/ml, 8.0 μg/ml, 16 μg/ml, and 32 μg/ml), cefotaxime (0.05 μg/ml, 0.1 μg/ml, 0.2 μg/ml, and 0.4 μg/ml), cefoxitin (0.75 μg/ml, 1.5 μg/ml, 3.0 μg/ml, and 6.0 μg/ml), puromycin (12 μg/ml, 25 μg/ml, 50 μg/ml, and 100 μg/ml), spectinomycin (3.5 μg/ml, 7.0 μg/ml, 14 μg/ml, and 28 μg/ml), fusidic acid (50 μg/ml, 100 μg/ml, 200 μg/ml, and 400 μg/ml), phosphomycin (0.2 μg/ml, 0.4 μg/ml, 0.8 μg/ml, and 1.6 μg/ml), phleomycin (0.25 μg/ml, 0.5 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), amikacin (0.25 μg/ml, 0.5 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), isoniazid (300 μg/ml, 600 μg/ml, 1200 μg/ml, 2400 μg/ml), ethionamide (25 μg/ml, 50 μg/ml, 100 μg/ml, and 200 μg/ml), SDS (50 μg/ml, 100 μg/ml, 200 μg/ml, 400 μg/ml), dodecyltrimethyl ammonium bromide (10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml), BIGCHAP (2000 μg/ml, 4000 μg/ml, 8000 μg/ml, and 16,000 μg/ml), niaproof (0.08%, 0.16%, 0.32%, and 0.64%), CHAPS (1500 μg/ml, 3000 μg/ml, 6000 μg/ml, 12,000 μg/ml), and N-lauryl sarcosine (1000 μg/ml, 2000 μg/ml, 4000 μg/ml and 8000 μg/ml). The wells of the ES3 plates contained the following antimicrobials (one compound at a particular concentration per well): nalidixic acid (0.5 μg/ml, 1.0 μg/ml, 2.0 μg/ml, 4.0 μg/ml), taurocholic acid (600 μg/ml, 1200 μg/ml, 2400 μg/ml, and 4800 μg/ml), colistin (0.25 μg/ml, 0.5 μg/ml, 1.0 μg/ml, and 2.0 μg/ml), procaine (2500 μg/ml, 5000 μg/ml, 10,000 μg/ml, and 20,000 μg/ml), diamide (16.6 μg/ml, 33.3 μg/ml, 66.6 μg/ml, and 133 μg/ml), hydroxylamine (12 μg/ml, 25 μg/ml, 50 μg/ml, and 100 μg/ml), guanidine (500 μg/ml, 1000 μg/ml, 2000 μg/ml, and 4000 μg/ml), cupric chloride (20 μg/ml, 40 μg/ml, 80 μg/ml, and 160 μg/ml), zinc chloride (10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml), cadmium chloride (5.0 μg/ml, 10 μg/ml, 20 μg/ml, and 40 μg/ml), nickel chloride (20 μg/ml, 40 μg/ml, 80 μg/ml, and 160 μg/ml), chromium chloride (100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml), sodium selenite (100 μg/ml, 200 μg/ml, 300 μg/ml, and 400 μg/ml), potassium tellurite (0.2 μg/ml, 0.4 μg/ml, 0.8 μg/ml, and 1.6 μg/ml), manganese sulfate (100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml), cobalt chloride (12 μg/ml, 25 μg/ml, 50 μg/ml, and 100 μg/ml), silver chloride (2.0 μg/ml, 4.0 μg/ml, 8.0 μg/ml, and 16 μg/ml), potassium chromate (10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml), potassium bromide (225 μg/ml, 450 μg/ml, 900 μg/ml, and 1800 μg/ml), sodium cyanate (155 μg/ml, 310 μg/ml, 600 μg/ml, and 1200 μg/ml), sodium azide (500 μg/ml, 1000 μg/ml, 2000 μg/ml, and 4000 μg/ml), picolinic acid (50 μg/ml, 100 μg/ml, 200 μg/ml, and 400 μg/ml), potassium superoxide (100 μg/ml, 200 μg/ml, 400 μg/ml, and 800 μg/ml) and menadione (3.3 μg/ml, 6.6 μg/ml, 13.3 μg/ml, and 26.6 μg/ml) The results of the first experiment indicated that in the presence of 10 μg/ml vancomycin, the E. coli strain tested exhibited transient increased sensitivity only to vancomycin at 10 μg/ml, 20 μg/ml, 40 μg/ml, and 80 μg/ml. In addition, the strain exhibited increased sensitivity to novobiocin at 33 μg/ml and 66 μg/ml, trimethoprim at 0.17 ng/ml, 0.33 ng/ml, 0.67 ng/ml, and 1.3 ng ml, cefazolin at 2.0 μg/ml and 4.0 μg/ml, cephalothin at 10 μg/ml and 20 μg/ml, cefoxitin at 0.75 μg/ml and 1.5 μg/ml, fusidic acid at 200 μg/ml and 400 μg/ml, and nalidixic acid at 1.0 μg/ml, 2.0 μg/ml, and 4.0 μg/ml. Normal sensitivity levels were observed for the other tests in the ESI, ES2 and ES3 microarray panels. The results also indicated that in the presence of 235 μg/ml sulfamethoxazole, the E. coli strain exhibited increased resistance to chlortetracycline at 0.25 μg/ml, 0.50 μg/ml, and 1.0 μg/ml, tetracycline at 0.033 μg/ml, 0.066 μg/ml, 0.133 μg/ml, and 0.266 μg/ml, novobiocin at 66 μg/ml and 133 μg/ml, but exhibited increased sensitivity to trimethoprim at 0.17 ng/ml, 0.33 ng/ml, 0.67 ng/ml, and 1.3 ng/ml, cephaloridine at 0.75 μg/ml, 1.5 μg/ml, 3.0 μg/ml, and 6.0 μg/ml, azomycin at 0.2 μg/ml, 0.4 μg/ml, 0.8 μg/ml, and 1.6 μg/ml, cefazolin at 0.5 μg/ml, 1.0 μg/ml, 2.0 μg/ml, and 4.0 μg/ml, cephalothin at 5.0 μg/ml, 10 μg/ml, and 20 μg/ml, cefaclor at 1.33 μg/ml, 2.66 μg/ml, and 5.33 μg/ml, cefsulodin at 8 μg/ml and 16 μg/ml, nickel chloride at 20 μg/ml and 40 μg/ml, chromium chloride at 200 μg/ml and 400 μg/ml, and cobalt chloride 12 μg/ml and 25 μg/ml. Normal sensitivity levels were observed for the other tests in the ESI, ES2 and ES3 microarray panels. Thus, this Example clearly illustrates the use of the present invention to test for synergy and/or antagonism using combinations of BACs. EXAMPLE 2 Antimicrobial Testing In this Example, experiments are described in which the feasibility of using PMs for analyzing the metabolic effects of antimicrobial compounds and their mechanisms of action were investigated. Specifically, the experiments were designed to determine whether compounds that act via interaction with specific bacterial proteins ("target- specific") can be distinguished from those acting via non-specific mechanisms, solely on the basis of differences in signature metabolic profiles. In addition, the experiments were designed to determine whether different interactors of the same pathway produce a similar signature profile, as well as whether interactors of different pathways produce distinctly different profiles. Twenty chemicals were selected for inclusion in these experiments. Fifteen of these, listed below in Table 3 as "single target antimicrobials" are thought to have relatively specific modes of action, whereas five antimicrobials, listed as "multiple target antimicrobials" are thought to have non-specific modes of action. Among the single target compounds were three sets of antimicrobials with similar modes of action on the cell wall (ampicillin, cephalothin, phosphomycin, and bacitracin), ribosomes (chloramphenicol, streptomycin, and tetracycline), or DNA gyrases (nalidixic acid, oxolinic acid, and coumermycin). An initial set of experiments was performed to select the concentrations of each chemical as it was desirable to use a partially inhibitory concentration. A completely inhibitory or sub-inhibitory concentration would not provide any information. Partial inhibitory levels were determined using the criterion of decreased formation of purple color due to inhibition of tetrazolium violet reduction (i.e., respiration). Each compound was tested at two concentrations giving partial inhibition of respiration. The lower concentration, referred to as "lx," was the lowest concentration giving detectable inhibition of respiration. The higher concentration, referred to as "2x," was twice the lx concentration. For most chemicals, another doubling to 4x gave a completely inhibitory level that would not be useful. Thus, only lx and 2x concentrations were used. It was determined that the selection of chemical concentration is an important parameter to control. However, the selection criteria used herein was found to be quite adequate. Only canavanine appeared to need a slightly higher concentration to give comparable results. If the concentration is chosen properly, only one concentration should be needed for the assay. Table 3. Compounds Used and Their Modes of Action In these experiments, E. coli MG1655 was tested against 20 antimicrobials at two concentrations using 7 PMs each, for a total of 280 PMs. PMs without any antimicrobial (a set of 7) were run each day as a control (this total does not include data from the control strains). Since in these experiments each PM contains 95 phenotypes, the total number of phenotypes analyzed here was 26,600. Each PM was monitored kinetically every 15 minutes using a specialized instrument described is U.S. Patent Appln. Ser. No. 09/277,353 (herein incorporated by reference) for an incubation duration of 48 hours. Thus, the total number of data points for the experiments was 5,107,200. Bioinformatics software (Biolog™) as used to analyze these data. The results of the data collected for a run is a kinetic phenotype of the cell exposed to an antimicrobial overlaid and compared against the phenotype of the cell without exposure to the antimicrobial. When the two kinetic tracings of tetrazolium reduction (i.e., cell respiration) overlap, there is no difference in the response to that phenotype (indicated as "O"). When the control tracing exceeds the antimicrobial tracing, the organism is scored as "more sensitive" or "S." When the antimicrobial tracing exceeds the control tracing, the organism is scored as "more resistant," or "R." Based on visual examination of the PMs after incubation, the threshold values for judging S and R results were determined. The software then automatically calculated the areas under the differential tracings and applied threshold values to score all 26,600 phenotypes as S, O, or R. From the S-O-R data, a distance matrix was generated. The S-O-R response (a string of 665 values) for one antimicrobial was compared to the response for another antimicrobial, and the differences summed up. A difference of O to S or of O to R was assigned a value of 1 , and a difference of S to R was assigned a value of 2. The string of 665 differences was then summed up. Pairs of antimicrobials with similar responses had lower difference values and pairs of antimicrobials with very different responses had higher difference values. The comparison of all pairs provides a distance matrix which can be used as input for algorithms that generate various cluster diagrams to help simplify and summarize the data. The results indicated a wide variation in the response of the organism to different classes of antimicrobials. For example, Figure 4 shows a dendrogram of the data obtained at the lx level of each antimicrobial. The four cell wall inhibitors (ampicillin, cephalothin, phosphomycin, and bacitracin) cluster, as do the three ribosome inhibitors (chloramphenicol, streptomycin, and tetracycline). Also, two out of the three of the DNA gyrase inhibitors (oxolinic acid and coumermycin) clustered. All of the single target antimicrobials except sulfathiazole and polymyxin B are in the tightly clustered center of the dendrogram, while all of the multiple target antimicrobials except canavanine are in the distant periphery of the dendrogram. First, these results indicate that the present invention can be be used to differentiate single target from multiple target antimicrobials. The multiple target antimicrobials make cells broadly and non-specifically hypersensitive, whereas the single target antimicrobials have a more specific "fingerprint." Second, this fingerprint pattern appears to successfully permit grouping of antimicrobials based upon their mode of action and differentiates them from other antimicrobials with different modes of action. In one case, the results were not as simple as expected. In this case, nalidixic acid did not cluster with the other two DNA gyrase inhibiting chemicals. This may indicate something about the mechanism of action of this drug. In addition, polymyxin B, cerulenin and sulfathiazole gave results that more closely resembled the multiple target antimicrobials. Polymyxin B and cerulenin both affect membrane synthesis and this may disrupt many cellular properties, as well as enhance the non-specific permeation of other antimicrobials. EXAMPLE 3 BAC Testing of Yeast In this Example, the response of a yeast to various compounds was tested. The yeast used in these experiments was Saccharomyces cerevisiae (BY4741, obtained from Dr. Mark Johnston, Washington University, St. Louis, MO). The genotype of this strain was indicated as being Mat a (i.e., mating type "a"), ura-, his-, leu-, and met-. In these experiments, the ability of this strain to grow in a culture medium without methionine was investigated. Methionine interferes with the ability to test this organism for its utilization of other potential sulfur sources (i.e., if methionine is added to a culture medium the organism preferentially uses it as a sulfur source). The yeast was grown for 48 hours at 30°C on R2A agar medium (Acumedia). Cells were removed from the agar surface with a sterile cotton swab and suspended at a cell density of 65% transmittance (as read using a Biolog™ turbidimeter) in an inoculating fluid containing 50 mM glucose, 0.15 mM uracil, 0.15 mM L-histidine, 0.15 mM L-leucine, 0.15 mM MgCl 2 , 1.0 mM CaCl 2 , 2.0 mM NaCl, 1.0 mM KC1, 3.0 mM NH 4 C1, 1.0 mM NaH 2 PO 4 , 0.1 mM Na^O^ 0.01% iodo-nitro-tetrazolium violet, 0.01% phytagel (gellan gum), 0.03% pluronic F-68; the pH was adjusted to 6.0. The cell suspension (100 μl/well) was then used to inoculate a Biolog™ EA MicroPlate™, which tests the ability of a cell to be stimulated by a set of 95 different nutrients. The nutrients included within the microarray were: LB medium (10 g/L tryptone, 5 g/L yeast extract, and 5 g/L NaCl), L-alanine (25 μM), L-arginine (25 μM), L-asparagine (25 μM), L-aspartic acid (25 μM), L-cysteine (25 μM), L-glutamic acid (25 μM), adenosine 3',5'-cyclic monophosphate (100 μM), adenine (100 μM), adenosine (100 μM), 2'-deoxyadenosine (100 μM), L-glutamine (25 μM), glycine (25 μM), L- histidine (25 μM), L-isoleucine (25 μM), L-leucine (25 μM), L-lysine (25 μM), L- methionine (25 μM), L-phenylalanine (25 μM), guanosine 3 ',5 '-cyclic monophosphate (100 μM), guanine (100 μM), guanosine (100 μM), 2'-deoxyguanosine (100 μM), L- proline (25 μM), L-serine (25 μM), L-threonine (25 μM), L-tryptophan (25 μM), L- tyrosine (25 μM), L-valine (25 μM), L-isoleucine and L-valine (25 μM each), trans-4- hydroxy L-proline (25 μM), (5) 4-aminoimidazole-4(5)-carboxamide (1 mM), hypoxanthine (100 μM), inosine (100 μM), 2'-deoxyinosine (100 μM), L-ornithine (100 μM), L-citrulline (100 μM), chorismic acid (100 μM), (-) shikimic acid (100 μM), L- homoserine lactone (100 μM), D-alanine (25 μM), D-aspartic acid (25 μM), D-glutamic acid (25 μM), DL-α,ε-diaminopimetic acid (25 μM), cytosine (100 μM), cytidine (100 μM), 2-deoxycytidine (100 μM), putrescine (25 μM), spermidine (25 μM), spermine (25 μM), pyridoxine (0.25 μM), pyridoxal (0.25 μM), pyridoxamine (0.25 μM), β-alanine (0.25 μM), D-pantothenic acid (0.25 μM), orotic acid (1 mM), uracil (100 μM), uridine (100 μM), 2'-deoxyuridine (100 μM), quinolinic acid (0.25 μM), nicotinic acid (0.25 μM), nicotinamide (0.25 μM), β-nicotinamide adenosine dinucleotide (0.25 μM), δ- amino-levulinic acid (0.25 μM), hematin (0.25 μM), deferoxamine mesylate (0.25 μM), glucose (1 mM), N-acetyl-D-glucosamine (100 μM), thymine (100 μM), glutathione (reduced form; 100 μM), thymidine (100 μM), oxaloacetic acid (1 mM), d-biotin (0.25 μM), cyanobalamine (0.25 μM), p-aminobenzoic acid (0.25 μM), folic acid (0.25 μM), inosine (100 μM) and thiamine (25 μM), thiamine (0.25 μM), thiamine pyrophosphate (0.25 μM), riboflavin (0.25 μM), pyrrolo-quinoline quinone (0.25 μM), menadione (0.25 μM), myo-inositol (0.25 μM), butyric acid (100 μM), DL-α-hydroxybutyric acid (100 μM), -ketobutyric acid (100 μM), caprylic acid (100 μM), DL-cc-lipoic acid (oxidized form; 0.25 μM), DL-mevalonic acid (0.25 μM), DL-carnitine (0.25 μM), choline (0.25 μM), Tween-20 (0.01%), Tween-40 (0.01%), Tween-60 (0.01%), and Tween-80 (0.01%). One well (A-l) contains no nutrients and is used as a reference (i.e., control) well. After inoculation, the microarray was incubated at 30°C for 2 days and visually observed. Any well that contained nutrient that stimulated growth of the cells had a higher level of pink color due to increased cell respiration and reduction of the iodo- nitro-tetrazolium violet dye. Three wells showed increased pink color. These wells were the wells which contained L-methionine, glutathione and pyridoxine. It was expected that methionine would be stimulatory, but it was unexpected that glutathione and pyridoxine would be stimulatory and could be used to substitute for methionine. In this case, because the ability of the organism to utilize various sulfur sources was being tested, glutathione could not be used as it also contains sulfur. However, pyridoxine does not contain sulfur, and could be used as a totally satisfactory replacement for methionine as a nutrient for S. cerevisiae strain BY4741. Thus, instead of growing and testing BY4741 on minimal media containing uracil, L-histidine, L-leucine, and L-methionine, it is possible to grow and test this strain on minimal media containing uracil, L-histidine, L- leucine, and pyridoxine. From the above Examples, it is clear that the present invention represents an unexpected and much improved system for the broad-based, rapid phenotype array testing of microorganisms and/or other cell types with BACs, in many uses and formats (or configurations), as well as for antimicrobial development and research. In addition, both automated and manual systems with fixed time point or kinetic reading may be used in conjunction with the present invention. For example, the results may be observed visually (i.e., by eye) by the person conducting the test, without assistance from a machine. Alternatively, the results may be obtained with the use of equipment (e.g., a microtiter plate reader) that measures transmittance, absorbance, or reflectance through, in, or from each well of a multitest device such as a microtiter testing plate (e.g., MicroPlate™) or a miniaturized testing card (e.g., MicroCard™). Kinetic readings may be obtained by taking readings at frequent time intervals or reading the test results continuously over time. One example of a device particularly suited for incubating and conducting the methods of the present invention includes the device described in co- pending U.S. Patent Application Serial Nos. 09/277,353, and 09/267,039, both of which are hereby incorporated by reference. In embodiments utilizing the multitest gel-matrix, the invention provides numerous advances and advantages over the prior art, including: (1) much greater safety, as there is no spillage, nor aerosolization of cells, mycelia, nor spores, while performing or inoculating test wells; (2) faster biochemical reactions are produced, giving final results hours or days earlier than commonly used methods; (3) more positive biochemical or phenotypic reactions are obtained, giving a truer picture of the microorganisms' metabolic characteristics; (4) darker, more clear-cut biochemical reactions and color changes are obtained; (5) more uniform color and/or turbidity are obtained, as the cells, mycelia, and/or spores do not settle and clump together at the bottom of the wells, nor do they adhere to the sides of the wells; (6) the reactions are much easier to observe visually or with optical instruments (e.g., the Biolog MicroStation Reader™); and (7) the overall process for performing multiple tests is extremely simple and efficient, requiring very little labor on the part of the biologist. All of these advantages enhance the speed and accuracy of scoring test results in studies to perform comparative phenotype analysis for the assessment of BACs using any cell type, including microbial strains.

Claims: CLAIMS What is claimed is: 1. A method for testing the response of at least two cells to at least one biologically active chemical comprising the steps of: (a) providing: i) a testing device having at least two wells, wherein each well of said testing device contains a defined medium comprising at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates; ii) a first suspension comprising a first cell and at least one biologically active chemical; and iii) a second suspension comprising a second cell and at least one biologically active chemical; (b) inoculating said first and second suspensions into said wells of said testing device; and (c) observing the response of said at first and second cells to said at least one biologically active chemical. 2. The method of Claim 1, wherein said testing device is selected from the group consisting of microtiter plates and microcards. 3. The method of Claim 1, wherein said suspension further comprises a gelling agent. 4. The method of Claim 1, wherein said testing device further comprises a gel-initiating agent in said wells. 5. The method of Claim 1, wherein said suspension further comprises a colorimetric indicator. 6. The method of Claim 1, wherein said testing device further comprises a colorimetric indicator in said wells. 7. The method of Claim 1, wherein said observing is visual. 8. The method of Claim 1, wherein said observing is performed by an instrument. 9. The method of Claim 1, wherein said response of said first and second cells is non-radioactive. 10. The method of Claim 1, wherein said first and second cells are eukaryotic cells. 11. The method of Claim 10, wherein said eukaryotic cells are animal cells. 12. The method of Claim 11, wherein said animal cells are mammalian cells. 13. The method of Claim 12, wherein said mammalian cells are human cells. 14. The method of Claim 11, wherein said mammalian cells are mutant cells. 15. The method of Claim 10, wherein said first and second cells are fungal cells. 16. The method of Claim 1, wherein said first and second cells are prokaryotic. 17. The method of Claim 16, wherein said prokaryotic cells are selected from the group consisting of eubacteria and archaebacteria. 18. The method of Claim 1, wherein said drug comprises at least one antimicrobial. 19. A method for comparing the effect of at least two biologically active chemicals comprising: a) providing: i) a first cell suspension comprising at least one cell type and at least one biologically active chemical, ii) a second cell suspension comprising the same said at least one cell type as in step i) and at least one biologically active chemical wherein said biologically active chemical is different from said biologically active chemical in said first cell suspension, iii) a first testing device having wells, wherein said wells contain defined medium comprising at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates, iv) a second testing device having wells, wherein said wells contain at least one substrate selected from the group consisting of carbon sources, nitrogen sources, phosphorus sources, sulfur sources, growth stimulating nutrients, drugs, and chromogenic testing substrates, and b) adding said first cell suspension to said wells of said first testing device to provide a first phenotype array; c) adding said second cell suspension to said wells of said second testing device to provide a second phenotype array; d) incubating said first and said second phenotype arrays; e) observing the response of said cell suspensions in said first and second phenotype arrays; and f) comparing the response of said first cell suspension in said first phenotype array with the response of said second cell suspension in said second phenotype array. 20. The method of Claim 19, wherein said first and second testing devices are selected from the group consisting of microtiter plates and microcards. 21. The method of Claim 19, wherein said first and second cell suspensions further comprise a gelling agent. 22. The method of Claim 19, wherein said first and second testing devices further comprise a gel-initiating agent in said wells. 23. The method of Claim 19, wherein said first and second cell suspensions further comprise a colorimetric indicator. 24. The method of Claim 19, wherein said first and second testing devices further comprise a colorimetric indicator in said wells. 25. The method of Claim 19, wherein said first testing device contains the same substrates as said second testing device. 26. The method of Claim 19, wherein said observing is visual. 27. The method of Claim 19, wherein said observing is performed by an instrument. 28. The method of Claim 19, wherein said response of said first and second cells is non-radioactive. 29. The method of Claim 19, wherein said comparison of said response is performed using multi-dimensional pattern analysis. 30. The method of Claim 19, wherein said first and second cells are eukaryotic cells. 31. The method of Claim 30, wherein said eukaryotic cells are animal cells. 32. The method of Claim 30, wherein said animal cells are mammalian cells. 33. The method of Claim 32, wherein said mammalian cells are human cells. 34. The method of Claim 32, wherein said mammalian cells are mutant cells. 35. The method of Claim 30, wherein said first and second cells are fungal cells. 36. The method of Claim 19, wherein said first and second cells are prokaryotic. 37. The method of Claim 36, wherein said prokaryotic cells are selected from the group consisting of eubacteria and archaebacteria. 38. The method of Claim 17, wherein said drug comprises at least one antimicrobial.

Inventors: BOCHNER BARRY, BOCHNER, BARRY
Applicants: BIOLOG INC, BOCHNER BARRY, BIOLOG, INC., BOCHNER, BARRY
Application year: 2001
Main classification: G01N33
IPC codes: C12Q1, C12R1, G01N33