During a 2-year period, 1,892 patients underwent biliary tract surgery at the Mayo Clinic. Both aerobic and anaerobic cultures of bile were performed in 371 of these patients. Sixty-nine percent of the cultures were positive, and 41% (117) of these grew anaerobes, although they were present in pure culture only twice. Mixed cultures most commonly contained four different organisms (three aerobes and one anaerobe). Bacteroides fragilis was the single most commonly isolated anaerobe and ranked fourth in terms of overall isolates behind Escherichia coli, group D streptococci, and Klebsiella B. fragilis accounted for 7.0% of the total group D streptococci, and Klebsiella. B. fragilis accounted for 7.0% of the total aerobic and anaerobic isolates and was present in 21% of all positive cultures. Pseudomonas aeruginosa and Clostridium perfringens ranked fifth and sixth, providing 6.5 and 5.9% of all isolates, respectively. This study demonstrates the frequent presence of anaerobes in patients with bactibilia and suggests that they be considered in the formulation of antimicrobial therapy for infections involving human biliary tracts.
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