Biochemical properties of beta-lactamase produced by Bacteroides distasonis

Three of 29 clinical isolates of Bacteroides distasonis strains, GAI2095, GAI2361 and GAI6270 were found to produce high levels of beta-lactamase relative to the remaining 26 strains. The enzymes from these strains showed a broad substrate profile, hydrolyzing cephaloridine, cephalothin, cefazolin, oxyimino-cephalosporins such as cefuroxime, cefotaxime and cefmenoxime, and piperacillin at high rates. Examination of the substrate profiles indicated that the enzymes were mainly oxyimino-cephalosporinases. Inactivation of latamoxef over a long time by crude enzyme extracts of GAI2095 and GAI2361 was detected by a microbiological assay. The enzyme activities were inhibited by imipenem, cefoxitin, clavulanic acid and sulbactam but not by EDTA. The majority of beta-lactamase activity was found in the cell extract prepared by ultrasonic treatment, especially in the precipitate by ultracentrifugation including membrane fraction. When the cells of B. distasonis were subjected to osmotic shock, negligible levels of beta-lactamase activity were found in the supernatant fluid. The enzymes appeared to be tightly associated with the cell envelope since detergents were required to elute these activities.