Changes in prevalence and susceptibility of obligate anaerobes in clinical veterinary practice.

Of 3,133 clinical specimens obtained from domestic animals, 26% contained species of bacteria that were obligate anaerobes. Members of the genera Bacteroides, Fusobacterium, and Peptostreptococcus accounted for 77% of the isolates. On the average, 2 species of obligate anaerobes were found in each specimen, usually admixed with facultatively anaerobic bacteria. Of those specimens containing an obligate anaerobe, 20% contained one isolate that was resistant to penicillin, ampicillin, and cephalothin. These resistant isolates belonged to the genus Bacteroides, the most common being Bacteroides fragilis. Approximately one third of these penicillin-resistant isolates was resistant to tetracycline as well. All isolates were susceptible to chloramphenicol, tetracycline (excluding penicillin-resistant Bacteroides), metronidazole, and clindamycin.