Characterization of broad-spectrum Mycobacterium abscessus class A -lactamase

Imipenem and cefoxitin are used to treat Mycobacterium abscessus infections and have moderate activity against this fast-growing mycobacterium (MIC50 of 16 and 32 mg/L, respectively). M. abscessus is highly resistant to most other β-lactams, although the underlying mechanisms have not been explored. Here, we characterized M. abscessus class A β-lactamase (BlaMab) and investigated its role in β-lactam resistance. Hydrolysis kinetic parameters of purified BlaMab were determined by spectrophotometry for various β-lactams and compared with those of related BlaC from Mycobacterium tuberculosis. MICs of β-lactams were determined for M. abscessus CIP104536 and for Escherichia coli producing BlaMab and BlaC. BlaMab had a broad hydrolysis spectrum, similar to that of BlaC, but with overall higher catalytic efficiencies, except for cefoxitin. As expected from its in vivo efficacy, cefoxitin was very slowly hydrolysed by BlaMab (kcat/Km = 6.7 M−1 s−1). BlaMab hydrolysed imipenem more efficiently (kcat/Km = 3.0×104 M−1 s−1), indicating that the in vivo activity of this drug might be improved by combination with a β-lactamase inhibitor. β-Lactamase inhibitors clavulanate, tazobactam and sulbactam did not inhibit BlaMab. This enzyme efficiently hydrolysed clavulanate, in contrast to BlaC, which is irreversibly acylated by this inhibitor. BlaMab and BlaC were functional in E. coli and the resistance profiles mediated by these enzymes were in agreement with the kinetic parameters. M. abscessus produces a clavulanate-insensitive broad-spectrum β-lactamase that limits the in vivo efficacy of β-lactams.