Previous chapters in this manual have frequently referred to anaerobic bacterial infections and anaerobic bacteria. Anaerobic bacterial infections may occur in virtually any body tissue and at any body site provided that the prevailing conditions are suitable.
The majority of anaerobic bacterial diseases are caused by endogenous bacteria that are part of the normal body flora and that are perfectly compatible with health until something happens to disturb the balance of the normal flora, or to allow the passage of bacteria from one anatomical site to another. Exogenous anaerobic bacteria, primarily Clostridium tetani, C. botulinum, and occasionally C. perfringens and other clostridial species, can gain access through wounds, causing tetanus, wound botulism, or gas gangrene. Abscesses of practically any organ, bacteraemia, peritonitis, thoracic empyema, cellulitis, and appendicitis are just a few conditions in which anaerobic bacteria may play a very significant role in the disease process. It is therefore important that the microbiologist knows when and how to culture for anaerobic bacteria in a given clinical specimen.