Susceptibility ofBacteroides non-fragilis and fusobacteria to amoxicillin,amoxicillin/clavulanate,ticarcillin, ticarcillin/clavulanate,cefoxitin, imipenem and metronidazole

The susceptibility of 234Bacteroides non-fragilis strains and 56 fusobacteria from 12 European centers to amoxicillin, amoxicillin/clavulanate, ticarcillin, ticarcillin/clavulanate, cefoxitin, imipenem and metronidazole was tested and related to -lactamase production. Beta-lactamase production was detected in 42.3 % of theBacteroides strains and 26.8 % of the fusobacteria. The MIC90 of amoxicillin for -lactamase-negative strains was 0.5 µg/ml and the MIC90 of ticarcillin 2.0 µg/ml. In the case of -lactamase-positive strains the MIC90 of amoxicillin (32 µg/ml) and ticarcillin (16 µg/ml) dropped to 1.0 µg/ml upon addition of clavulanate; 65.8 % of these strains were susceptible to amoxicillin and 98.2 % to ticarcillin, but all were susceptible when clavulanate was added. All strains were susceptible to imipenem and metronidazole, and 99.3 % to cefoxitin.