Microbiology

The branch of pathology that deals with the identificaton and study of infectious organisms. Specimens of blood, urine, faeces, sputum, discharges, pus, cerebrospinal fluid and fluid aspirated from joints, cysts and other body cavities are sent to the microbiology laboratory. If infection is sus pected, solid tissues such as biopsy specimens may also be sent for testing by slicing, staining, and searching for micro-organisms under a microscope.

The usual procedure with liquid samples is for fresh and stained smears of the fluid to be immediately examined under a microscope. If many organ isms are present, as for example in pus. it may be possible to identify the cause of the infection at once. Some of the specimen is added to one or more culture mediums (often a broth or jelly) specially prepared to nurture particular organisms. The cultures are then incubated for various periods before being examined to see whether organisms have grown. The organism is identified by microscopic examination or by testing for its specific antigens. When some bacteria are cultured they are tested against a range of antibiotics to see whether they are sensitive or resistant to them.

The use of these techniques of culture and sensitivity testing has made the diagnosis of many infectious diseases very accurate, and saved much futile antibiotic treatment. Culture and sensitivity testing for bacteria takes 48 hours. Fungi may be identified immediately in a fresh specimen, but may take several weeks to culture. Some viruses can be quickly identified by immunological tests, but may also take weeks to culture.

Types of microbiology

• Microbial physiology.
• Microbial genetics.
• Environmental microbiology.
• Veterinary microbiology.
• Evolutionary microbiology.
• Aeromicrobiology.
• Pharmaceutical microbiology.