Sulfamethoxazole: A bacteriostatic antibacterial agent that interferes with folic acid synthesis in susceptible bacteria. Its broad spectrum of activity has been limited by the development of resistance. (From Martindale, The Extra Pharmacopoeia, 30th ed, p208)Trimethoprim: A pyrimidine inhibitor of dihydrofolate reductase, it is an antibacterial related to PYRIMETHAMINE. It is potentiated by SULFONAMIDES and the TRIMETHOPRIM, SULFAMETHOXAZOLE DRUG COMBINATION is the form most often used. It is sometimes used alone as an antimalarial. TRIMETHOPRIM RESISTANCE has been reported.Trimethoprim-Sulfamethoxazole Combination: This drug combination has proved to be an effective therapeutic agent with broad-spectrum antibacterial activity against both gram-positive and gram-negative organisms. It is effective in the treatment of many infections, including PNEUMOCYSTIS PNEUMONIA in AIDS.Trimethoprim Resistance: Nonsusceptibility of bacteria to the action of TRIMETHOPRIM.Anti-Bacterial Agents: Substances that reduce the growth or reproduction of BACTERIA.Anti-Infective Agents: Substances that prevent infectious agents or organisms from spreading or kill infectious agents in order to prevent the spread of infection.Microbial Sensitivity Tests: Any tests that demonstrate the relative efficacy of different chemotherapeutic agents against specific microorganisms (i.e., bacteria, fungi, viruses).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).Pneumonia, Pneumocystis: A pulmonary disease in humans occurring in immunodeficient or malnourished patients or infants, characterized by DYSPNEA, tachypnea, and HYPOXEMIA. Pneumocystis pneumonia is a frequently seen opportunistic infection in AIDS. It is caused by the fungus PNEUMOCYSTIS JIROVECII. The disease is also found in other MAMMALS where it is caused by related species of Pneumocystis.Pneumocystis jirovecii: A species of PNEUMOCYSTIS infecting humans and causing PNEUMOCYSTIS PNEUMONIA. It also occasionally causes extrapulmonary disease in immunocompromised patients. Its former name was Pneumocystis carinii f. sp. hominis.Drug Resistance, Multiple, Bacterial: The ability of bacteria to resist or to become tolerant to several structurally and functionally distinct drugs simultaneously. This resistance may be acquired through gene mutation or foreign DNA in transmissible plasmids (R FACTORS).Pentamidine: Antiprotozoal agent effective in trypanosomiasis, leishmaniasis, and some fungal infections; used in treatment of PNEUMOCYSTIS pneumonia in HIV-infected patients. It may cause diabetes mellitus, central nervous system damage, and other toxic effects.Integrons: DNA elements that include the component genes and insertion site for a site-specific recombination system that enables them to capture mobile gene cassettes.Urinary Tract Infections: Inflammatory responses of the epithelium of the URINARY TRACT to microbial invasions. They are often bacterial infections with associated BACTERIURIA and PYURIA.Stenotrophomonas maltophilia: A species of STENOTROPHOMONAS, formerly called Xanthomonas maltophilia, which reduces nitrate. It is a cause of hospital-acquired ocular and lung infections, especially in those patients with cystic fibrosis and those who are immunosuppressed.Gram-Negative Bacterial Infections: Infections caused by bacteria that show up as pink (negative) when treated by the gram-staining method.Ciprofloxacin: A broad-spectrum antimicrobial carboxyfluoroquinoline.Enterobacteriaceae: A family of gram-negative, facultatively anaerobic, rod-shaped bacteria that do not form endospores. Its organisms are distributed worldwide with some being saprophytes and others being plant and animal parasites. Many species are of considerable economic importance due to their pathogenic effects on agriculture and livestock.Opportunistic Infections: An infection caused by an organism which becomes pathogenic under certain conditions, e.g., during immunosuppression.Escherichia coli Infections: Infections with bacteria of the species ESCHERICHIA COLI.Otitis Media: Inflammation of the MIDDLE EAR including the AUDITORY OSSICLES and the EUSTACHIAN TUBE.Dapsone: A sulfone active against a wide range of bacteria but mainly employed for its actions against MYCOBACTERIUM LEPRAE. Its mechanism of action is probably similar to that of the SULFONAMIDES which involves inhibition of folic acid synthesis in susceptible organisms. It is also used with PYRIMETHAMINE in the treatment of malaria. (From Martindale, The Extra Pharmacopoeia, 30th ed, p157-8)Anti-Infective Agents, Urinary: Substances capable of killing agents causing urinary tract infections or of preventing them from spreading.Community-Acquired Infections: Any infection acquired in the community, that is, contrasted with those acquired in a health care facility (CROSS INFECTION). An infection would be classified as community-acquired if the patient had not recently been in a health care facility or been in contact with someone who had been recently in a health care facility.Staphylococcal Infections: Infections with bacteria of the genus STAPHYLOCOCCUS.Folic Acid Antagonists: Inhibitors of the enzyme, dihydrofolate reductase (TETRAHYDROFOLATE DEHYDROGENASE), which converts dihydrofolate (FH2) to tetrahydrofolate (FH4). They are frequently used in cancer chemotherapy. (From AMA, Drug Evaluations Annual, 1994, p2033)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.Methicillin-Resistant Staphylococcus aureus: A strain of Staphylococcus aureus that is non-susceptible to the action of METHICILLIN. The mechanism of resistance usually involves modification of normal or the presence of acquired PENICILLIN BINDING PROTEINS.Cross Infection: Any infection which a patient contracts in a health-care institution.Sulfadiazine: One of the short-acting SULFONAMIDES used in combination with PYRIMETHAMINE to treat toxoplasmosis in patients with acquired immunodeficiency syndrome and in newborns with congenital infections.Sulfisoxazole: A short-acting sulfonamide antibacterial with activity against a wide range of gram- negative and gram-positive organisms.Tetrahydrofolate Dehydrogenase: An enzyme of the oxidoreductase class that catalyzes the reaction 7,8-dihyrofolate and NADPH to yield 5,6,7,8-tetrahydrofolate and NADPH+, producing reduced folate for amino acid metabolism, purine ring synthesis, and the formation of deoxythymidine monophosphate. Methotrexate and other folic acid antagonists used as chemotherapeutic drugs act by inhibiting this enzyme. (Dorland, 27th ed) EC 1.5.1.3.Staphylococcus aureus: Potentially pathogenic bacteria found in nasal membranes, skin, hair follicles, and perineum of warm-blooded animals. They may cause a wide range of infections and intoxications.Serotyping: Process of determining and distinguishing species of bacteria or viruses based on antigens they share.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).Drug Combinations: Single preparations containing two or more active agents, for the purpose of their concurrent administration as a fixed dose mixture.Drug Hypersensitivity: Immunologically mediated adverse reactions to medicinal substances used legally or illegally.Prevalence: The total number of cases of a given disease in a specified population at a designated time. It is differentiated from INCIDENCE, which refers to the number of new cases in the population at a given time.Drug Administration Schedule: Time schedule for administration of a drug in order to achieve optimum effectiveness and convenience.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Tropheryma: A genus of gram-positive bacteria in the family Cellulomonadaceae.R Factors: A class of plasmids that transfer antibiotic resistance from one bacterium to another by conjugation.4-Aminobenzoic Acid: An aminobenzoic acid isomer that combines with pteridine and GLUTAMIC ACID to form FOLIC ACID. The fact that 4-aminobenzoic acid absorbs light throughout the UVB range has also resulted in its use as an ingredient in SUNSCREENS.Shigella sonnei: A lactose-fermenting bacterium causing dysentery.Drug Synergism: The action of a drug in promoting or enhancing the effectiveness of another drug.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Shigella: A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria that ferments sugar without gas production. Its organisms are intestinal pathogens of man and other primates and cause bacillary dysentery (DYSENTERY, BACILLARY).Conjugation, Genetic: A parasexual process in BACTERIA; ALGAE; FUNGI; and ciliate EUKARYOTA for achieving exchange of chromosome material during fusion of two cells. In bacteria, this is a uni-directional transfer of genetic material; in protozoa it is a bi-directional exchange. In algae and fungi, it is a form of sexual reproduction, with the union of male and female gametes.Nocardia Infections: Infections with bacteria of the genus NOCARDIA.Dihydropteroate Synthase: An enzyme that catalyzes the formation of dihydropteroate from p-aminobenzoic acid and dihydropteridine-hydroxymethyl-pyrophosphate. EC 2.5.1.15.Whipple Disease: A chronic systemic infection by a gram-positive bacterium, Tropheryma whippelii, mainly affecting the SMALL INTESTINE but also the JOINTS; CARDIOVASCULAR SYSTEM; and the CENTRAL NERVOUS SYSTEM. The disease is characterized by fat deposits in the INTESTINAL MUCOSA and LYMPH NODES, malabsorption, DIARRHEA with fatty stools, MALNUTRITION, and ARTHRITIS.Sulfamethoxypyridazine: A sulfanilamide antibacterial agent.Tetracycline: A naphthacene antibiotic that inhibits AMINO ACYL TRNA binding during protein synthesis.Ampicillin: Semi-synthetic derivative of penicillin that functions as an orally active broad-spectrum antibiotic.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)Salmonella: A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria that utilizes citrate as a sole carbon source. It is pathogenic for humans, causing enteric fevers, gastroenteritis, and bacteremia. Food poisoning is the most common clinical manifestation. Organisms within this genus are separated on the basis of antigenic characteristics, sugar fermentation patterns, and bacteriophage susceptibility.Pneumocystis: A genus of ascomycetous FUNGI, family Pneumocystidaceae, order Pneumocystidales. It includes various host-specific species causing PNEUMOCYSTIS PNEUMONIA in humans and other MAMMALS.Sulfonamides: A group of compounds that contain the structure SO2NH2.Megaloblasts: Red blood cell precursors, corresponding to ERYTHROBLASTS, that are larger than normal, usually resulting from a FOLIC ACID DEFICIENCY or VITAMIN B 12 DEFICIENCY.DNA, Bacterial: Deoxyribonucleic acid that makes up the genetic material of bacteria.Nocardia: A genus of gram-positive, aerobic bacteria whose species are widely distributed and are abundant in soil. Some strains are pathogenic opportunists for humans and animals.Nalidixic Acid: A synthetic 1,8-naphthyridine antimicrobial agent with a limited bacteriocidal spectrum. It is an inhibitor of the A subunit of bacterial DNA GYRASE.Salmonella enterica: A subgenus of Salmonella containing several medically important serotypes. The habitat for the majority of strains is warm-blooded animals.Vibrio cholerae O1: Strains of VIBRIO CHOLERAE containing O ANTIGENS group 1. All are CHOLERA-causing strains (serotypes). There are two biovars (biotypes): cholerae and eltor (El Tor).Atovaquone: A hydroxynaphthoquinone that has antimicrobial activity and is being used in antimalarial protocols.Dysentery, Bacillary: DYSENTERY caused by gram-negative rod-shaped enteric bacteria (ENTEROBACTERIACEAE), most often by the genus SHIGELLA. Shigella dysentery, Shigellosis, is classified into subgroups according to syndrome severity and the infectious species. Group A: SHIGELLA DYSENTERIAE (severest); Group B: SHIGELLA FLEXNERI; Group C: SHIGELLA BOYDII; and Group D: SHIGELLA SONNEI (mildest).Enterobacteriaceae Infections: Infections with bacteria of the family ENTEROBACTERIACEAE.Feces: Excrement from the INTESTINES, containing unabsorbed solids, waste products, secretions, and BACTERIA of the DIGESTIVE SYSTEM.Electrophoresis, Gel, Pulsed-Field: Gel electrophoresis in which the direction of the electric field is changed periodically. This technique is similar to other electrophoretic methods normally used to separate double-stranded DNA molecules ranging in size up to tens of thousands of base-pairs. However, by alternating the electric field direction one is able to separate DNA molecules up to several million base-pairs in length.Haptens: Small antigenic determinants capable of eliciting an immune response only when coupled to a carrier. Haptens bind to antibodies but by themselves cannot elicit an antibody response.Cholera: An acute diarrheal disease endemic in India and Southeast Asia whose causative agent is VIBRIO CHOLERAE. This condition can lead to severe dehydration in a matter of hours unless quickly treated.Salmonella Infections, Animal: Infections in animals with bacteria of the genus SALMONELLA.Bacterial Infections: Infections by bacteria, general or unspecified.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.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.