Pathophysiology of abscess formation

Clinical and experimental data provide evidence for interactions between aerobic and anaerobic organisms in abscess formation. The organisms present represent a subset of those normally found at nearby mucosal surfaces. Certain organisms, most notably B. fragilis, emerge from the normal flora as important in abscess formation. Suspected virulence factors for B. fragilis include oxygen tolerance, capsular polysaccharide and the other enzymes produced by this organism. Other factors, as yet incompletely understood, probably play a role. In addition, the large number of organisms present in an abscess, the presence of antibiotic inactivating enzymes, the hostility of the anaerobic environment to antimicrobial activity and host defences, as well as the fibrous capsule surrounding an abscess, contribute to the persistence of infection despite antibiotic therapy and the need for drainage. The contribution of both aerobic and anaerobic organisms in the formation of abscesses must be remembered when one chooses antibiotic therapy for such infections.