NONINDUCIBLE, MAINLY CELL-ASSOCIATED BETA-LACTAMASE FROM NOCARDIA-ASTEROIDES STRAIN-108

The beta-lactamase of the soil-borne strain 108 (parental strain) of N ocardia asteroides is a non-inducible enzyme mainly associated with th e cells; it can be efficiently extracted by ultrasonication and SDS tr eatment. Crude enzyme preparations showed penicillinase and cephalospo rinase activity. The kinetics of beta-lactamase production and in-vitr o susceptibility to combinations of beta-lactam antibiotics plus beta- lactamase inhibitors have been studied in two stable overproducer muta nts (A14 and B1) obtained by mutagenization of the parental strain wit h nitrosoguanidine. The cell-associated enzyme increased with bacteria l growth in parental and mutant strains and was particularly abundant in stationary phase cells. The beta-lactamase inhibitors sulbactam and clavulanic acid decreased MIC values of penicillins more efficiently in the parental strain than in mutants, thus indicating some involveme nt of the enzyme in the resistance of N. asteroides strain 108 to beta -lactam antibiotics.