A collaborative study of French laboratories to assess any evolution of antibiotic resistance within the Bacteroides fragilis group.

Antibiotic susceptibility testing of anaerobes by a same methodology allows the authors to draw up suggestions about the evolution of antibiotic resistance within the B. fragilis group. Cefoxitin resistance rates were stable until 1985 and were slowly increasing later. Until 1985 piperacillin was able to inhibit all tested strains. In 1987 the two groups noticed an increasing resistance to piperacillin (4 to 9%). During the 1970's clindamycin resistance was a minor event (less than 1%) then the resistance rate increased rapidly to 10% in 1980. MICs determinations from 1981 to 1985 demonstrated well that clindamycin resistance was stable at this 10% rate. Since 1987 the clindamycin resistance was again increasing and reached respectively 14 to 19% for the two groups of investigators. Metronidazole has kept a good activity against Bacteroides fragilis group strains but some strains with reduced susceptibility (MIC 2 to 8 mg/l) have been described since 1983. Three strains with MIC greater than 8 mg/l were recently described by one of the groups. Until 1987, the clavulanic amoxicillin combination was able to inhibit all strains of the B. fragilis group but only imipenem remained still active on all investigated strains with no change at all for the values of MIC50 and MIC90 determined by the investigators of this study. All these results emphasize the need for periodical surveys within the B. fragilis group in each country.