Chapter 9 - Anaerobic infections

Abstract

This chapter discusses anaerobic infections. An anaerobe is a microbe that can only grow under anaerobic conditions. In a laboratory, an organism of which the identity is in doubt may be subcultured both anaerobically with added carbon dioxide and aerobically with added carbon dioxide, with the plates incubated for at least five days. A microaerophilic, carbon dioxide-dependent coccus may, for example, appear on the aerobic plate on the fifth day even though it was apparent on the anaerobic plate on the second day. A strict anaerobe will only grow on the anaerobic plate. A simple classification that has clinical relevance is to divide anaerobes into two groups: (1) the non-sporing anaerobes and (2) the spore-forming anaerobes. Non-sporing anaerobes die quickly in an aerobic environment, as they do not form spores, and are also relatively easily killed by heat and chemical disinfectants. Spore-forming anaerobes frequently form spores in hostile environments, and these spores may survive for many years. The spores resist drying many chemical disinfectants and are not always killed by boiling water at 100°C. The spore-forming anaerobes consist of many species of clostridia that are anaerobic Gram-positive bacilli.