Antibiotic susceptibility of anaerobic bacteria in Europe.

Twenty-two laboratories in 15 European countries determined the MICs of 12 antibiotics for 1,289 isolates of the B. fragilis group by a microdilution method. There was no resistance to metronidazole (breakpoint, 8 mg/L), and only one isolate was found to be resistant to chloramphenicol (breakpoint, 8 mg/L). Resistance was uncommon to imipenem (0.3% at concentrations > 4 mg/L), amoxicillin/clavulanate (1% at concentrations > 8 mg/L), cefoxitin (3% at concentrations > 32 mg/L), mezlocillin (6% at concentrations > 64 mg/L), and clindamycin (9% at concentrations > 4 mg/L). The majority of the isolates were resistant to ampicillin (93% at concentrations > 4 mg/L), ciprofloxacin (56% at concentrations > 4 mg/L), and tetracycline (64% at concentrations > 4 mg/L). Bacteroides fragilis was the most susceptible species of the group, and the most striking regional differences in susceptibility were found in association with clindamycin and tetracycline; more resistance was noted in isolates from the southern part of Europe (Greece, Italy, Portugal, and Spain). It has been reported that Fusobacterium species and Clostridium species occasionally produce beta-lactamases. A few metronidazole-resistant Clostridium perfringens strains but no metronidazole-resistant fusobacteria have been isolated.