OXACILLIN-HYDROLYZING BETA-LACTAMASE INVOLVED IN RESISTANCE TO IMIPENEM IN ACINETOBACTER-BAUMANNII

Acinetobacter baumannii strain A148, a clinical isolate resistant to i mipenem (MIC=32 mg l(-1)), synthesized two beta-lactamases with pIs 6. 3 and >9.2. The pI 6.3 enzyme hydrolyzed the penicillins, including is oxazoylpenicillins, first-, second- and, to a lesser extent, third-gen eration cephalosporins. It was inhibited by chloride ions and by the p enem beta-lactamase inhibitor BRL 42715. Clavulanate was a weak inhibi tor and EDTA did not affect the beta-lactamase activity. This enzyme a lso hydrolyzed imipenem with a catalytic efficiency (k(cat)/K-m) of 15 00 mM(-1) s(-1). Moreover, this purified beta-lactamase produced a pos itive microbiological clover-leaf test with imipenem. Therefore, the p I 6.3 beta-lactamase was considered to be involved in the imipenem res istance of A. baumannii strain A148.