Properties of β-lactamases produced by three species of mycobacteria

Abstract

1. Mycobacterium smegmatis (N.C.T.C. 8158), M. fortuitum and M. phlei (MPI) produce a constitutive beta-lactamase that has penicillinase and cephalosporinase activity. 2. The beta-lactamases of these three species of acid-fast bacteria were mainly cell-bound, only small amounts of activity being liberated into the extracellular fluid. The total beta-lactamase activity of these mycobacteria was much lower than that of certain Gram-positive organisms, but comparable with that reported for species of Gram-negative bacteria. 3. The beta-lactamases of intact cells of the mycobacteria were not freely accessible to any of the substrates tested, but the apparent crypticity factor to benzylpenicillin was greater than that to cephaloridine and cephalosporin C. 4. Attempts to induce beta-lactamase activity in M. smegmatis and M. phlei failed even with high concentrations of inducer. 5. The beta-lactamases obtained from the three species of mycobacteria showed different substrate specificities, including different relative activities as cephalosporinases and penicillinases respectively. 6. Certain derivatives of 6-aminopenicillanic acid and 7-aminocephalosporanic acid were found to be resistant to hydrolysis by beta-lactamases of M. smegmatis and M. fortuitum. 7. The beta-lactamase of M. smegmatis was competitively inhibited by a number of beta-lactamase-resistant derivatives of 6-aminopenicillanic acid, but not by similar derivatives of 7-aminocephalosporanic acid.