Isolation and antimicrobial susceptibility of obligate anaerobic bacteria recovered from the uteri of dairy cows with retained fetal membranes and postparturient endometritis.

The uteri of 77 postparturient dairy cows were sampled. Samples were cultured aerobically and anaerobically, and the nature of bacterial growth was identified. A mixed aerobic and anaerobic bacterial infection was found in 55% of the samples. Actinomyces pyogenes was the predominant aerobic species; it was found in 70% of the samples, whereas Bacteroides melaninogenicus was the most frequent anaerobic species isolated. Altogether, 16 species belonging to the genus Bacteroides were identified with variable frequencies. It appears that more than one Bacteroides species colonizes the uterus of a given cow postpartum. The minimal inhibitory concentrations (MICs) of clindamycin, metronidazole, tetracycline and ciprofloxacin for 83 anaerobic isolates were determined. All isolates were susceptible to clindamycin (MIC90 of 0.064 microgram/ml) and all but two to metronidazole. Susceptibility to ciprofloxacin was variable, with a bimodal distribution of MIC values. The MIC of tetracycline for 90% of the isolates was > 256 micrograms/ml.