The antibiotic sensitivity of the Bacteroides fragilis group in the United Kingdom.

Eight hundred and sixty-two cultures of penicillin-resistant anaerobic Gram-negative bacilli collected from 14 centres in the United Kingdom were identified. Six hundred and fifty-one were members of the Bacteroides fragilis group, and their sensitivity to 14 antibiotics was determined by a microtitre method. Among the beta-lactams, moderate resistance to ampicillin (MIC greater than or equal to 8 mg/l) was common, (B. ovatus 100%, B. thetaiotaomicron 95%, B. fragilis 76%, B. distasonis 50%, B. vulgatus 25%) but high-level resistance (MIC greater than 128 mg/l) was uncommon (B. fragilis 4%, B. ovatus 4%, B. vulgatus 3%). In B. fragilis, moderate resistance to other beta-lactams was less common (cefoxitin 16%, mezlocillin 13% and cefotetan 7%), though in most non-B. fragilis species, higher numbers were moderately resistant. High level resistance to these three beta-lactams was rare. Resistance to penems (MIC greater than 4 mg/l) was not detected. All isolates of B. fragilis tested were sensitive to 16 mg/l of ciprofloxacin and ofloxacin, and 68% and 81% of isolates were sensitive to less than 4 mg/l, but one isolate of B. uniformis and one of B. thetaiotaomicron proved highly resistant. Clindamycin resistance was uncommon (1% of B. fragilis and 10% other B. fragilis group isolates were resistant to 2 mg/l clindamycin) with isolates resistant to clindamycin often also resistant to erythromycin. Tetracycline resistance was common in all species and occurred in 40% of isolates. Resistance to chloramphenicol, metronidazole or rifampicin was not detected. Significant differences were observed between the sensitivity of B. fragilis and other members of the B. fragilis group to mezlocillin, cefotetan, cefoxitin and the quinolones. There was no clear trend towards higher resistance in any one area of the country.