BACTERICIDAL ACTIVITY OF SELECTED ANTIMICROBIAL AGENTS AGAINST BILOPHILA-WADSWORTHIA AND BACTEROIDES-GRACILIS

Bactericidal assays of Bacteroides gracilis (six strains) and Bilophila wadsworthia (12 strains) in brucella broth with appropriate supplements were performed by the time-kill kinetic method. Antimicrobial agents tested were ampicillin/sulbactam (final concentrations, 16/8 mug/mL), ticarcillin/clavulanate (128/2 mug/mL), imipenem (8 mug/mL), cefoxitin (32 mug/mL), chloramphenicol (16 mug/mL), clindamycin (4 mug/mL), and metronidazole (16 mug/mL). Although all antimicrobial agents tested inhibited growth of all Bilophila strains during the first 24 hours, bactericidal activity was variable; only metronidazole was uniformly bactericidal. Most strains of Bilophila showed 1-2 log increases in growth at 6 hours with clindamycin and chloramphenicol. With chloramphenicol, some Bilophila strains tested showed regrowth starting at 30 hours. B. gracilis strains were generally more susceptible to all agents tested. Metronidazole, ticarcillin/clavulanate, chloramphenicol, and imipenem were most active. Several strains of B. gracilis were not killed by ampicillin/sulbactam, clindamycin, or cefoxitin. Activity was variable among strains and antimicrobial agents.