Microbiology of polymicrobial abscesses and implications for therapy

Abscesses that develop as a result of introduction of the normal flora into a normally sterile body site are often polymicrobial. This review summarizes past studies published by our group on the microbiology of polymicrobial abscesses that occur at various body sites. Staphylococcus aureus and Group A beta-haemolytic streptococci are the most prevalent aerobes in skin and soft tissue abscesses and are isolated at all body sites. In contrast, organisms that colonize the mucous membranes predominated in infections adjacent to these membranes. In this fashion, organisms of the gastrointestinal and cervical flora (enteric Gram-negative bacilli and Bacteroides fragilis group) were found most often in intra-abdominal and buttock and leg lesions. Group A beta-haemolytic streptococci, pigmented Prevotella and Porphyromonas spp., and Fusobacterium spp. were most commonly found in lesions of the mouth, head, neck and fingers. These organisms probably reached these sites from the oral cavity, where they are part of the normal flora. Drainage of the abscess is the treatment of choice. Appropriate management of these mixed aerobic and anaerobic infections may also require the administration of antimicrobials that are effective against both the aerobic and anaerobic components of the infections.