Clindamycin resistance transfer in Bacteroides fragilis.

Clindamycin is one of the antimicrobial agents most commonly used against anaerobes. Resistance to clindamycin in Bacteroides fragilis has been increasing recently. Thirty strains of clindamycin-resistant (including multi-resistant) B. fragilis were collected for study of cross-resistance to beta-lactam agents and beta-lactam--beta-lactamase inhibitor and resistance transferability. Imipenem was the most active drug against these 30 isolates. Resistance to clindamycin was transferred to a recipient in 12 out of 30 donor strains by using filter-mating. Of 12 transconjugants, only three had detectable plasmids by alkaline lysis method and the remaining nine strains lacked plasmids. The transfer frequencies ranged from 10(-4) to 10(-6). The role of plasmid in the resistance transfer was not certain. However, the results suggest that non-plasmid-mediated transfer accounted for the majority of the transfers of clindamycin-resistance of B. fragilis in this study. Tetracycline resistance was co-transferred from six donors. There was no evidence of co-transference of beta-lactam resistance under the selection marker of clindamycin, beta-lactam, or both. Therefore, non-plasmid-mediated transfer may play an important role in dissemination of resistance transfer in B. fragilis in Taiwan.