Expression and some properties of beta-lactamase from Mycobacterium fortuitum

Several species of mycobacteria have been reported to produce beta-lactamases, but only those of M. smegmatis have been purified and partially characterized. This study is a preliminary report of the presence of beta-lactamase activity in M. fortuitum, strain Cow 18. A partial purification of the beta-lactamase has also been achieved. M. fortuitum was grown in either Sauton or glucose-yeast extract medium (GYM) and sonicated cells or culture filtrates were assessed for the presence of beta-lactamase activity using a chromogenic compound (PADAC) as substrate. Cells growing in GYM medium released a detectable amount of enzyme, whereas microorganisms showed only intracellular beta-lactamase activity. The enzyme present in the culture filtrate of M. fortuitum Cow 18 was concentrated by Amicon ultrafiltration and partially purified through Sephadex G-75 and QAE-Sephadex A-50 ion exchanger columns. The spectrum of activity of this enzyme included some cephalosporins (cephaloridine, cephalothin) and some penicillins, the hydrolysis of the former being generally more pronounced. Furthermore, cefoxitin, ceftazidime and cefotaxime were not hydrolysed.