Anaerobic infections are usually endogenous and are caused by tissue invasion by bacteria normally resident on the respective body surface. Anaerobic bacteria are normally present on skin, mouth, nasopharyngeal and upper respiratory tract, intestines and vagina.
Anaerobic infections generally follow some precipitating factor such as trauma, tissue necrosis, impaired circulation, hematoma formation or the presence of foreign bodies. Diabetes, malnutrition, malignancy or prolonged treatment with aminoglycoside antibodies may act as predisposing factors.
Anaerobic infection is usually polymicrobial, more then one anaerobe is responsible besides aerobic bacteria. While the infection is usually localised, general dissemination may occur by bacteremia.
There are some clinical features which suggest the presence of anaerobic infection. Pus produced by anaerobes is characteristically putrid, with a pervasive, nauseating odor. Toxemia and fever are not marked.
As anaerobes form part of the normal flora of the skin and mucous surface, their isolation from specimens has to be interpreted cautiously.
Specimens should be collected in such a manner as to avoid resident flora. For example, the sputum is unsatisfactory for culture from a suspected case of lung abscess; only material collected by aspiration would be acceptable.
As some anaerobes die on exposure to oxygen, care should be exercised to minimize contact with air during collection, transport and handling of specimens. A satisfactory method of collection is to aspirate the specimen into an airtight syringe, plunge the needle into a sterile rubber cork to seal it and sand it immediately to the laboratory.Pus and other fluids may be collected in small bottles with airtight caps and transported quickly, ensuring that the specimens fill the bottles completely. Swabs are generally unsatisfactory but they are to be used, they should be sent in Stuart’s transport medium.