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 metalloenzymes. 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.