DISTRIBUTION AND CHARACTERIZATION OF BETA-LACTAMASES OF MYCOBACTERIA AND RELATED ORGANISMS

Setting: The detailed distribution and precise features of mycobacterial beta-lactamases urgently need to be elucidated. Objective: To study the distribution pattern of beta-lactamases among mycobacteria, their enzymatic profiles and degree of contribution to the expression of drug resistance of some mycobacteria to beta-lactam antibiotics. Design: Cell-associated beta-lactamase was measured by nitrocefin disc method. beta-lactamases obtained from some mycobacteria were studied for their substrate specificity, metal ion-dependency and isoelectric focusing (IEF) patterns. Changes in the minimum inhibitory concentrations (MICs) of beta-lactams for rapidly growing mycobacteria due to the combined use of tazobactam were measured. Results: In slow growers, Mycobacterium tuberculosis complex possessed strong and M. kansasii showed strong to intermediate beta-lactamase activity, while M. avium complex lacked such an activity. All the rapid growers possessed strong to intermediate activity. The beta-lactamases of test organisms including M. tuberculosis, M. kansasii, M. fortuitum etc, exerted both penicillinase and cephalosporinase activities and were not metallo-enzymes. M. tuberculosis, M. kansasii, and M. smegmatis exhibited the species-specific IEF patterns of beta-lactamases. Tazobactam potentiated the in vitro antimicrobial activities of some beta-lactams against M. fortuitum and M. chelonae. Conclusion: Many mycobacteria possessed peculiar beta-lactamases and the enzymes were partly attributable to their drug resistance to certain beta-lactam antibiotics.