Medical bacteriology

(medicine) A branch of medical microbiology that deals with the study of bacteria which affect human health, especially those which produce disease.

The study of bacteria that cause human disease. The field encompassesthe detection and identification of bacterial pathogens, determination of thesensitivity and mechanisms of resistance of bacteria to antibiotics, themechanisms of virulence, and some aspects of immunity to infection. See also Virulence.

The clinical bacteriology laboratory identifies bacterial pathogens presentin specimens such as sputum, pus, blood, and spinal fluid, or from swabs ofskin, throat, rectal, or urogenital surfaces. Identification involves directstaining and microscopic examination of these materials, and isolation ofbacteria present in the material by growth in appropriate media. The laboratorymust differentiate bacterial pathogens from harmless bacteria that colonizehumans. Species and virulent strains of bacteria can be identified on the basisof growth properties, metabolic and biochemical tests, and reactivity withspecific antibodies.

Recent advances in the field of diagnostic bacteriology have involvedautomation of biochemical testing; the development of rapid antibody-baseddetection methods; and the application of molecular biology techniques. Once a bacterial pathogen has beenidentified, a major responsibility of the diagnostic bacteriology laboratory isthe determination of the sensitivity of the pathogen to antibiotics. Thisinvolves observation of the growth of the bacteria in the presence of variousconcentrations of antibiotics. The process has been made more efficient by thedevelopment of automated instrumentation.

An increasingly serious problem in the therapy of infectious diseases is theemergence of antibiotic-resistant strains of bacteria. An important area ofresearch is the mechanisms of acquisition of antibiotic resistance and theapplication of this knowledge to the development of more effective antibiotics. See also Antibiotic; Antigen-antibody reaction; Bacterial physiology and metabolism; Bacterial taxonomy; Immunochemistry.

The study of bacterial pathogenesis involves the fields of moleculargenetics, biochemistry, cell biology, and immunology. In cases where thedisease is not serious and easily treated, research may involve the deliberateinfection of human volunteers. Otherwise, various models of human disease mustbe utilized. These involve experimental infection of animals and the use oftissue cell culture systems. Modern molecular approaches to the study ofbacterial pathogenesis frequently involve the specific mutation or eliminationof a bacterial gene thought to encode a virulence property, followed byobservation of the mutant bacteria in a model system of human disease. In thisway, relative contributions of specific bacterial traits to different stages of the disease process can be determined. This knowledge permits the design of effective strategies for intervention that will prevent or cure the disease. See also Bacterial genetics.

The presence of specific antibodies is frequently useful in the diagnosis of bacterial diseases in which the pathogen is otherwise difficult to detect. An example is the sexually transmitted disease syphilis; the diagnosis must be confirmed by the demonstration of antibodies specific for T. pallidum. See also Antibody; Biologicals.

Immunity to some bacteria that survive intracellularly is not mediated by antibodies but by immune effector cells, known as T cells, that activate infected cells to kill the bacteria that they contain. An active area of research is how bacterial components are presented to the immune system in a way that will induce effective cell-mediated immunity. This research may lead to the development of T-cell vaccines effective against intracellular bacterial pathogens.

For disease entities caused by specific bacteria See also Anthrax; Botulism; Brucellosis; Cholera; Diphtheria; Glanders; Gonorrhea; Granuloma inguinale; Johne's disease; Leprosy; Listeriosis; Plague; Pseudotuberculosis; Tuberculosis; Tularemia; Food poisoning; Infant diarrhea; Meningitis; Pneumonia; Haemophilus; Immunology; Medical bacteriology; Pneumococcus; Streptococcus.