Mycobacterium smegmatis: A rapid-growing, nonphotochromogenic species of MYCOBACTERIUM originally isolated from human smegma and found also in soil and water. (From Dorland, 28th ed)Mycobacterium: A genus of gram-positive, aerobic bacteria. Most species are free-living in soil and water, but the major habitat for some is the diseased tissue of warm-blooded hosts.Mycobacterium tuberculosis: A species of gram-positive, aerobic bacteria that produces TUBERCULOSIS in humans, other primates, CATTLE; DOGS; and some other animals which have contact with humans. Growth tends to be in serpentine, cordlike masses in which the bacilli show a parallel orientation.Mycobacterium bovis: The bovine variety of the tubercle bacillus. It is called also Mycobacterium tuberculosis var. bovis.Mycobacterium avium: A bacterium causing tuberculosis in domestic fowl and other birds. In pigs, it may cause localized and sometimes disseminated disease. The organism occurs occasionally in sheep and cattle. It should be distinguished from the M. avium complex, which infects primarily humans.Mycobacterium Infections: Infections with bacteria of the genus MYCOBACTERIUM.Nontuberculous Mycobacteria: So-called atypical species of the genus MYCOBACTERIUM that do not cause tuberculosis. They are also called tuberculoid bacilli, i.e.: M. buruli, M. chelonae, M. duvalii, M. flavescens, M. fortuitum, M. gilvum, M. gordonae, M. intracellulare (see MYCOBACTERIUM AVIUM COMPLEX;), M. kansasii, M. marinum, M. obuense, M. scrofulaceum, M. szulgai, M. terrae, M. ulcerans, M. xenopi.Mycobacteriophages: Viruses whose host is one or more Mycobacterium species. They include both temperate and virulent types.Mycobacterium Infections, Nontuberculous: Infections with nontuberculous mycobacteria (atypical mycobacteria): M. kansasii, M. marinum, M. scrofulaceum, M. flavescens, M. gordonae, M. obuense, M. gilvum, M. duvali, M. szulgai, M. intracellulare (see MYCOBACTERIUM AVIUM COMPLEX;), M. xenopi (littorale), M. ulcerans, M. buruli, M. terrae, M. fortuitum (minetti, giae), M. chelonae.Mycobacterium leprae: A species of gram-positive, aerobic bacteria that causes LEPROSY in man. Its organisms are generally arranged in clumps, rounded masses, or in groups of bacilli side by side.Bacterial Proteins: Proteins found in any species of bacterium.Mycobacterium fortuitum: A rapid-growing, nonphotochromogenic species that is potentially pathogenic, producing lesions of lung, bone, or soft tissue following trauma. It has been found in soil and in injection sites of humans, cattle, and cold-blooded animals. (Dorland, 28th ed)Mycolic AcidsMycobacterium avium Complex: A complex that includes several strains of M. avium. M. intracellulare is not easily distinguished from M. avium and therefore is included in the complex. These organisms are most frequently found in pulmonary secretions from persons with a tuberculous-like mycobacteriosis. Strains of this complex have also been associated with childhood lymphadenitis and AIDS; M. avium alone causes tuberculosis in a variety of birds and other animals, including pigs.Mycobacterium chelonae: A species of gram-positive, aerobic bacteria commonly found in soil and occasionally isolated from sputum. It causes postoperative wound infections as well as gluteal abscesses.Antitubercular Agents: Drugs used in the treatment of tuberculosis. They are divided into two main classes: "first-line" agents, those with the greatest efficacy and acceptable degrees of toxicity used successfully in the great majority of cases; and "second-line" drugs used in drug-resistant cases or those in which some other patient-related condition has compromised the effectiveness of primary therapy.Ethambutol: An antitubercular agent that inhibits the transfer of mycolic acids into the cell wall of the tubercle bacillus. It may also inhibit the synthesis of spermidine in mycobacteria. The action is usually bactericidal, and the drug can penetrate human cell membranes to exert its lethal effect. (From Smith and Reynard, Textbook of Pharmacology, 1992, p863)Mycobacterium phlei: A saprophytic bacterium widely distributed in soil and dust and on plants.Mycobacterium marinum: A moderate-growing, photochromogenic species found in aquariums, diseased fish, and swimming pools. It is the cause of cutaneous lesions and granulomas (swimming pool granuloma) in humans. (Dorland, 28th ed)Tuberculosis: Any of the infectious diseases of man and other animals caused by species of MYCOBACTERIUM.Mycobacterium kansasii: A slow-growing, photochromogenic species that is the etiologic agent of a tuberculosis-like disease in humans and is frequently isolated from human pulmonary secretions or tubercles. The incidence of infection is sharply increased among immunocompromised individuals. (Dorland, 28th ed)Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Mycobacterium avium subsp. paratuberculosis: A subspecies of gram-positive, aerobic bacteria. It is the etiologic agent of Johne's disease (PARATUBERCULOSIS), a chronic GASTROENTERITIS in RUMINANTS.Isoniazid: Antibacterial agent used primarily as a tuberculostatic. It remains the treatment of choice for tuberculosis.DNA, Bacterial: Deoxyribonucleic acid that makes up the genetic material of bacteria.Genes, Bacterial: The functional hereditary units of BACTERIA.Galactans: Polysaccharides composed of repeating galactose units. They can consist of branched or unbranched chains in any linkages.Gene Expression Regulation, Bacterial: Any of the processes by which cytoplasmic or intercellular factors influence the differential control of gene action in bacteria.Mycobacterium avium-intracellulare Infection: A nontuberculous infection when occurring in humans. It is characterized by pulmonary disease, lymphadenitis in children, and systemic disease in AIDS patients. Mycobacterium avium-intracellulare infection of birds and swine results in tuberculosis.Viomycin: A strongly basic peptide, antibiotic complex from several strains of Streptomyces. It is allergenic and toxic to kidneys and the labyrinth. Viomycin is used in tuberculosis as several different salts and in combination with other agents.Mycobacterium ulcerans: A slow-growing mycobacterium that infects the skin and subcutaneous tissues, giving rise to indolent BURULI ULCER.Cell Wall: The outermost layer of a cell in most PLANTS; BACTERIA; FUNGI; and ALGAE. The cell wall is usually a rigid structure that lies external to the CELL MEMBRANE, and provides a protective barrier against physical or chemical agents.Glycopeptides: Proteins which contain carbohydrate groups attached covalently to the polypeptide chain. The protein moiety is the predominant group with the carbohydrate making up only a small percentage of the total weight.Rifampin: A semisynthetic antibiotic produced from Streptomyces mediterranei. It has a broad antibacterial spectrum, including activity against several forms of Mycobacterium. In susceptible organisms it inhibits DNA-dependent RNA polymerase activity by forming a stable complex with the enzyme. It thus suppresses the initiation of RNA synthesis. Rifampin is bactericidal, and acts on both intracellular and extracellular organisms. (From Gilman et al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 9th ed, p1160)Antigens, Bacterial: Substances elaborated by bacteria that have antigenic activity.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Ergothioneine: A naturally occurring metabolite of HISTIDINE that has antioxidant properties.Microbial Sensitivity Tests: Any tests that demonstrate the relative efficacy of different chemotherapeutic agents against specific microorganisms (i.e., bacteria, fungi, viruses).Ethionamide: A second-line antitubercular agent that inhibits mycolic acid synthesis.Tuberculosis, Pulmonary: MYCOBACTERIUM infections of the lung.Glycolipids: Any compound containing one or more monosaccharide residues bound by a glycosidic linkage to a hydrophobic moiety such as an acylglycerol (see GLYCERIDES), a sphingoid, a ceramide (CERAMIDES) (N-acylsphingoid) or a prenyl phosphate. (From IUPAC's webpage)Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Alanine Racemase: A pyridoxal-phosphate protein that reversibly catalyzes the conversion of L-alanine to D-alanine. EC An isomer of glucose that has traditionally been considered to be a B vitamin although it has an uncertain status as a vitamin and a deficiency syndrome has not been identified in man. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1379) Inositol phospholipids are important in signal transduction.Cord Factors: Toxic glycolipids composed of trehalose dimycolate derivatives. They are produced by MYCOBACTERIUM TUBERCULOSIS and other species of MYCOBACTERIUM. They induce cellular dysfunction in animals.Drug Resistance, Bacterial: The ability of bacteria to resist or to become tolerant to chemotherapeutic agents, antimicrobial agents, or antibiotics. This resistance may be acquired through gene mutation or foreign DNA in transmissible plasmids (R FACTORS).Cycloserine: Antibiotic substance produced by Streptomyces garyphalus.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Culture Media: Any liquid or solid preparation made specifically for the growth, storage, or transport of microorganisms or other types of cells. The variety of media that exist allow for the culturing of specific microorganisms and cell types, such as differential media, selective media, test media, and defined media. Solid media consist of liquid media that have been solidified with an agent such as AGAR or GELATIN.Polysorbates: Sorbitan mono-9-octadecanoate poly(oxy-1,2-ethanediyl) derivatives; complex mixtures of polyoxyethylene ethers used as emulsifiers or dispersing agents in pharmaceuticals.Microbial Viability: Ability of a microbe to survive under given conditions. This can also be related to a colony's ability to replicate.Genetic Complementation Test: A test used to determine whether or not complementation (compensation in the form of dominance) will occur in a cell with a given mutant phenotype when another mutant genome, encoding the same mutant phenotype, is introduced into that cell.DNA Transposable Elements: Discrete segments of DNA which can excise and reintegrate to another site in the genome. Most are inactive, i.e., have not been found to exist outside the integrated state. DNA transposable elements include bacterial IS (insertion sequence) elements, Tn elements, the maize controlling elements Ac and Ds, Drosophila P, gypsy, and pogo elements, the human Tigger elements and the Tc and mariner elements which are found throughout the animal kingdom.Capreomycin: Cyclic peptide antibiotic similar to VIOMYCIN. It is produced by Streptomyces capreolus.Rhamnose: A methylpentose whose L- isomer is found naturally in many plant glycosides and some gram-negative bacterial lipopolysaccharides.Drug Resistance, Microbial: The ability of microorganisms, especially bacteria, to resist or to become tolerant to chemotherapeutic agents, antimicrobial agents, or antibiotics. This resistance may be acquired through gene mutation or foreign DNA in transmissible plasmids (R FACTORS).Methylmannosides: Mannosides formed by the reaction of the hydroxyl group on the anomeric carbon atom of mannose with methyl alcohol. They include both alpha- and beta-methylmannosides.Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Gene Deletion: A genetic rearrangement through loss of segments of DNA or RNA, bringing sequences which are normally separated into close proximity. This deletion may be detected using cytogenetic techniques and can also be inferred from the phenotype, indicating a deletion at one specific locus.RNA, Bacterial: Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.Anti-Bacterial Agents: Substances that reduce the growth or reproduction of BACTERIA.Streptomycin: An antibiotic produced by the soil actinomycete Streptomyces griseus. It acts by inhibiting the initiation and elongation processes during protein synthesis.Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Tuberculosis Vaccines: Vaccines or candidate vaccines used to prevent or treat TUBERCULOSIS.Mycobacterium lepraemurium: The etiologic agent of rat leprosy, also known as murine leprosy.Mycobacterium scrofulaceum: A non-tuberculous mycobacterium causing cervical lymphadenitis in children. It very rarely causes pulmonary disease, and is believed to be non-pathogenic in animals.Antibiotics, Antitubercular: Substances obtained from various species of microorganisms that are, alone or in combination with other agents, of use in treating various forms of tuberculosis; most of these agents are merely bacteriostatic, induce resistance in the organisms, and may be toxic.BCG Vaccine: An active immunizing agent and a viable avirulent attenuated strain of Mycobacterium tuberculosis, var. bovis, which confers immunity to mycobacterial infections. It is used also in immunotherapy of neoplasms due to its stimulation of antibodies and non-specific immunity.Chromatography, Thin Layer: Chromatography on thin layers of adsorbents rather than in columns. The adsorbent can be alumina, silica gel, silicates, charcoals, or cellulose. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Macrophages: The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood MONOCYTES. Main types are PERITONEAL MACROPHAGES; ALVEOLAR MACROPHAGES; HISTIOCYTES; KUPFFER CELLS of the liver; and OSTEOCLASTS. They may further differentiate within chronic inflammatory lesions to EPITHELIOID CELLS or may fuse to form FOREIGN BODY GIANT CELLS or LANGHANS GIANT CELLS. (from The Dictionary of Cell Biology, Lackie and Dow, 3rd ed.)Mutagenesis, Insertional: Mutagenesis where the mutation is caused by the introduction of foreign DNA sequences into a gene or extragenic sequence. This may occur spontaneously in vivo or be experimentally induced in vivo or in vitro. Proviral DNA insertions into or adjacent to a cellular proto-oncogene can interrupt GENETIC TRANSLATION of the coding sequences or interfere with recognition of regulatory elements and cause unregulated expression of the proto-oncogene resulting in tumor formation.Disaccharides: Oligosaccharides containing two monosaccharide units linked by a glycosidic bond.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Mycobacteriaceae: A family of gram-positive bacteria found in soil and dairy products and as parasites on animals and man. Several are important pathogens.Bacteriological Techniques: Techniques used in studying bacteria.Mycobacterium xenopi: A slow-growing, scotochromogenic species occurring usually harmlessly in human secretions but occasionally associated with chronic pulmonary disease. (Dorland, 28th ed)Paratuberculosis: A chronic GASTROENTERITIS in RUMINANTS caused by MYCOBACTERIUM AVIUM SUBSPECIES PARATUBERCULOSIS.Leprosy: A chronic granulomatous infection caused by MYCOBACTERIUM LEPRAE. The granulomatous lesions are manifested in the skin, the mucous membranes, and the peripheral nerves. Two polar or principal types are lepromatous and tuberculoid.Porins: Porins are protein molecules that were originally found in the outer membrane of GRAM-NEGATIVE BACTERIA and that form multi-meric channels for the passive DIFFUSION of WATER; IONS; or other small molecules. Porins are present in bacterial CELL WALLS, as well as in plant, fungal, mammalian and other vertebrate CELL MEMBRANES and MITOCHONDRIAL MEMBRANES.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Mannosides: Glycosides formed by the reaction of the hydroxyl group on the anomeric carbon atom of mannose with an alcohol to form an acetal. They include both alpha- and beta-mannosides.ArabinosePolymerase Chain Reaction: In vitro method for producing large amounts of specific DNA or RNA fragments of defined length and sequence from small amounts of short oligonucleotide flanking sequences (primers). The essential steps include thermal denaturation of the double-stranded target molecules, annealing of the primers to their complementary sequences, and extension of the annealed primers by enzymatic synthesis with DNA polymerase. The reaction is efficient, specific, and extremely sensitive. Uses for the reaction include disease diagnosis, detection of difficult-to-isolate pathogens, mutation analysis, genetic testing, DNA sequencing, and analyzing evolutionary relationships.Oxazoles: Five-membered heterocyclic ring structures containing an oxygen in the 1-position and a nitrogen in the 3-position, in distinction from ISOXAZOLES where they are at the 1,2 positions.Sequence Alignment: The arrangement of two or more amino acid or base sequences from an organism or organisms in such a way as to align areas of the sequences sharing common properties. The degree of relatedness or homology between the sequences is predicted computationally or statistically based on weights assigned to the elements aligned between the sequences. This in turn can serve as a potential indicator of the genetic relatedness between the organisms.Dihydrostreptomycin Sulfate: A semi-synthetic aminoglycoside antibiotic that is used in the treatment of TUBERCULOSIS.Genome, Bacterial: The genetic complement of a BACTERIA as represented in its DNA.Escherichia coli: A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.Genes, Essential: Those genes found in an organism which are necessary for its viability and normal function.Transformation, Bacterial: The heritable modification of the properties of a competent bacterium by naked DNA from another source. The uptake of naked DNA is a naturally occuring phenomenon in some bacteria. It is often used as a GENE TRANSFER TECHNIQUE.Tuberculosis, Bovine: An infection of cattle caused by MYCOBACTERIUM BOVIS. It is transmissible to man and other animals.Leprostatic Agents: Substances that suppress Mycobacterium leprae, ameliorate the clinical manifestations of leprosy, and/or reduce the incidence and severity of leprous reactions.Anti-Infective Agents: Substances that prevent infectious agents or organisms from spreading or kill infectious agents in order to prevent the spread of infection.Plasmids: Extrachromosomal, usually CIRCULAR DNA molecules that are self-replicating and transferable from one organism to another. They are found in a variety of bacterial, archaeal, fungal, algal, and plant species. They are used in GENETIC ENGINEERING as CLONING VECTORS.AmidohydrolasesMannosyltransferases: Enzymes that catalyze the transfer of mannose from a nucleoside diphosphate mannose to an acceptor molecule which is frequently another carbohydrate. The group includes EC, EC, EC, and EC Dehydrogenase: An NAD-dependent enzyme that catalyzes the reversible DEAMINATION of L-ALANINE to PYRUVATE and AMMONIA. The enzyme is needed for growth when ALANINE is the sole CARBON or NITROGEN source. It may also play a role in CELL WALL synthesis because L-ALANINE is an important constituent of the PEPTIDOGLYCAN layer.Nicotinamidase: An enzyme that catalyzes the hydrolysis of nicotinamide to nicotinate and ammonia. EC haemophilum: A species of gram-positive, aerobic bacteria that causes granulomatous or ulcerating skin lesions in immunosuppressed persons. This organism owes its name to its requirement for growth of high levels of iron, conveniently supplied as blood, heme, or ferric ammonium citrate.TrehaloseColony Count, Microbial: Enumeration by direct count of viable, isolated bacterial, archaeal, or fungal CELLS or SPORES capable of growth on solid CULTURE MEDIA. The method is used routinely by environmental microbiologists for quantifying organisms in AIR; FOOD; and WATER; by clinicians for measuring patients' microbial load; and in antimicrobial drug testing.Open Reading Frames: A sequence of successive nucleotide triplets that are read as CODONS specifying AMINO ACIDS and begin with an INITIATOR CODON and end with a stop codon (CODON, TERMINATOR).Acyltransferases: Enzymes from the transferase class that catalyze the transfer of acyl groups from donor to acceptor, forming either esters or amides. (From Enzyme Nomenclature 1992) EC 2.3.RNA, Ribosomal, 16S: Constituent of 30S subunit prokaryotic ribosomes containing 1600 nucleotides and 21 proteins. 16S rRNA is involved in initiation of polypeptide synthesis.Operon: In bacteria, a group of metabolically related genes, with a common promoter, whose transcription into a single polycistronic MESSENGER RNA is under the control of an OPERATOR REGION.Pyrazinamide: A pyrazine that is used therapeutically as an antitubercular agent.DNA Gyrase: A bacterial DNA topoisomerase II that catalyzes ATP-dependent breakage of both strands of DNA, passage of the unbroken strands through the breaks, and rejoining of the broken strands. Gyrase binds to DNA as a heterotetramer consisting of two A and two B subunits. In the presence of ATP, gyrase is able to convert the relaxed circular DNA duplex into a superhelix. In the absence of ATP, supercoiled DNA is relaxed by DNA gyrase.Substrate Specificity: A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.Kanamycin Resistance: Nonsusceptibility of bacteria to the antibiotic KANAMYCIN, which can bind to their 70S ribosomes and cause misreading of messenger RNA.Sputum: Material coughed up from the lungs and expectorated via the mouth. It contains MUCUS, cellular debris, and microorganisms. It may also contain blood or pus.Promoter Regions, Genetic: DNA sequences which are recognized (directly or indirectly) and bound by a DNA-dependent RNA polymerase during the initiation of transcription. Highly conserved sequences within the promoter include the Pribnow box in bacteria and the TATA BOX in eukaryotes.Glycine Dehydrogenase: An oxidoreductase that catalyzes the oxidative DEAMINATION of GLYCINE to glyoxylate and AMMONIA in the presence of NAD. In BACTERIA lacking transaminating pathways the enzyme can act in the reverse direction to synthesize glycine from glyoxylate and ammonia and NADH.Dianisidine: Highly toxic compound which can cause skin irritation and sensitization. It is used in manufacture of azo dyes.Phagosomes: Membrane-bound cytoplasmic vesicles formed by invagination of phagocytized material. They fuse with lysosomes to form phagolysosomes in which the hydrolytic enzymes of the lysosome digest the phagocytized material.Mannose: A hexose or fermentable monosaccharide and isomer of glucose from manna, the ash Fraxinus ornus and related plants. (From Grant & Hackh's Chemical Dictionary, 5th ed & Random House Unabridged Dictionary, 2d ed)Gene Knockout Techniques: Techniques to alter a gene sequence that result in an inactivated gene, or one in which the expression can be inactivated at a chosen time during development to study the loss of function of a gene.Armadillos: Burrowing, chiefly nocturnal mammals of the family Dasypodidae having bodies and heads encased in small bony plates. They are widely distributed in the warmer parts of the Americas.Siderophores: Low-molecular-weight compounds produced by microorganisms that aid in the transport and sequestration of ferric iron. (The Encyclopedia of Molecular Biology, 1994)Bacterial Typing Techniques: Procedures for identifying types and strains of bacteria. The most frequently employed typing systems are BACTERIOPHAGE TYPING and SEROTYPING as well as bacteriocin typing and biotyping.Recombinant Proteins: Proteins prepared by recombinant DNA technology.Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization: A mass spectrometric technique that is used for the analysis of large biomolecules. Analyte molecules are embedded in an excess matrix of small organic molecules that show a high resonant absorption at the laser wavelength used. The matrix absorbs the laser energy, thus inducing a soft disintegration of the sample-matrix mixture into free (gas phase) matrix and analyte molecules and molecular ions. In general, only molecular ions of the analyte molecules are produced, and almost no fragmentation occurs. This makes the method well suited for molecular weight determinations and mixture analysis.Fatty Acid Synthases: Enzymes that catalyze the synthesis of FATTY ACIDS from acetyl-CoA and malonyl-CoA derivatives.Tuberculosis, Multidrug-Resistant: Tuberculosis resistant to chemotherapy with two or more ANTITUBERCULAR AGENTS, including at least ISONIAZID and RIFAMPICIN. The problem of resistance is particularly troublesome in tuberculous OPPORTUNISTIC INFECTIONS associated with HIV INFECTIONS. It requires the use of second line drugs which are more toxic than the first line regimens. TB with isolates that have developed further resistance to at least three of the six classes of second line drugs is defined as EXTENSIVELY DRUG-RESISTANT TUBERCULOSIS.Kinetics: The rate dynamics in chemical or physical systems.Virulence: The degree of pathogenicity within a group or species of microorganisms or viruses as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenic capacity of an organism is determined by its VIRULENCE FACTORS.Nitroreductases: Enzymes which reduce nitro groups (NITRO COMPOUNDS) and other nitrogenous compounds.