Aerobic and anaerobic microbiology of retroperitoneal abscesses.

The aerobic and anaerobic microbiology of various types of retroperitoneal abscesses was studied by review of the clinical and laboratory data for 161 patients treated between 1974 and 1990 for such abscesses. These included 109 anterior, 8 posterior, 21 retrofascial, and 23 pelvic retroperitoneal abscesses. A total of 472 organisms (2.9 isolates/specimen)--204 aerobic and facultative (1.3/specimen), and 268 anaerobic (1.7/specimen)--were recovered. Aerobes only were recovered from 34 abscesses (21%), anaerobes only from 34 (21%), and mixed aerobic and anaerobic bacteria from 93 (58%). Polymicrobial infection was present in 132 patients (82%). The predominant aerobic and facultative isolates were Escherichia coli (60 isolates), Klebsiella pneumoniae (20), Streptococcus group D (19), and Staphylococcus aureus (11). The predominant anaerobes were Peptostreptococcus species (95 isolates), Bacteroides fragilis group (66), Prevotella species (22), and Clostridium species (22). The number of anaerobes per site always was greater than the number of aerobic or facultative organisms and was especially high in pelvic abscesses. The number of aerobic and facultative organisms was especially high in pancreatic abscesses. These data highlight the polymicrobial aerobic-anaerobic nature of retroperitoneal abscesses.