In-vitro susceptibilities of species of the Bacteroides fragilis group to newer beta-lactam agents

The in-vitro activities of imipenem and four beta-lactam-beta-lactamase inh ibitor combinations were tested against 816 strains of the Bacteroides frag ilis group, and compared with other anti-anaerobic agents. None of the stra ins was resistant to metronidazole, and only one was resistant to chloramph enicol. Mezlocillin and piperacillin were moderately active, while clindamy cin was the least active. Rates of resistance varied between various specie s. The new beta-lactam agents tested showed excellent activity; piperacilli n-tazobactam and imipenem were the most active. The emergence of strains th at are resistant to these agents, observed in this study, suggests there is a need to perform periodic antimicrobial susceptibility tests.