In vitro activities of 17 antimicrobial agents against the formate/fumarate-requiring, anaerobic gram-negative bacilli.

The in vitro activities of 17 antimicrobial agents were evaluated against 46 clinical isolates of formate/fumarate-requiring anaerobic gram-negative bacilli. Strains of Bacteroides ureolyticus (23) were almost uniformly susceptible to the tested antimicrobials, whereas strains of Bacteroides gracilis (18) showed some striking resistance with penicillin active against only 67%, the cephalosporins active against 67%-89%, and clindamycin active against 67%. Although few strains of Wolinella species/C. concisus (5) were available for testing, these isolates tended to be more resistant than B. ureolyticus but less resistant than B. gracilis.