Occurrence of clindamycin-resistant anaerobic bacteria isolated from cultures taken following clindamycin therapy.

MICs of clindamycin were determined by the agar dilution method against anaerobic organisms isolated from endometrial cultures in women with pelvic soft tissue infections. Cultures were obtained from 100 women both before and after clindamycin therapy, from 107 women before therapy with clindamycin or another antimicrobial agent or after treatment with an antimicrobial agent other than clindamycin, and from 9 women 1 to 9 weeks after they were discharged from the hospital following clindamycin therapy. Only 5 (0.7%) of 685 isolates tested from women who had not received clindamycin therapy were resistant to clindamycin. From the 100 cultures taken immediately after clindamycin therapy, 57 anaerobic bacteria were isolated from 28 cultures. Of the 40 anaerobic organisms for which MICs of clindamycin were determined, 25 (62.5%) were resistant to clindamycin (MIC greater than or equal to 8 micrograms/ml). The most common organisms isolated after therapy were the anaerobic gram-positive cocci (of which 32 isolates were discovered); of 28 coccal isolates tested, 64% were clindamycin resistant. Four of seven (57%) of the Bacteroides isolates tested, one unidentified gram-positive nonsporing rod, one unidentified gram-negative coccus, and one Mobiluncus sp. were also clindamycin resistant. Of 18 anaerobic isolates from the nine cultures taken 1 to 9 weeks after hospital discharge, 55% were resistant to clindamycin. The clinical significance of these findings is unknown since all patients recovered without incident and remained well. However, the data suggest that physicians need to be aware that patients with recent exposure to clindamycin may have clindamycin-resistant anaerobic organisms in a current infection. This may prevent the infection from responding to clindamycin treatment.