In Vitro Activity of the New β-Lactamase Inhibitors Relebactam and Vaborbactam in Combination with β-Lactams against Mycobacterium abscessus Complex Clinical Isolates

Pulmonary disease due to infection with Mycobacterium abscessus complex (MABC) is notoriously difficult to treat, in large part due to the intrinsic resistance of MABC strains to most antibiotics, including beta-lactams. MABC organisms express a broad-spectrum beta-lactamase that is resistant to traditional beta-lactam-based beta-lactamase inhibitors but inhibited by a newer non-beta-lactam-based beta-lactamase inhibitor, avibactam. Consequently, the susceptibility of MABC members to some beta-lactams is increased in the presence of avibactam. Therefore, we hypothesized that two new non-beta-lactam-based beta-lactamase inhibitors, relebactam and vaborbactam, would also increase the susceptibility of MABC organisms to beta-lactams. The objective of the present study was to evaluate the in vitro activity of various marketed beta-lactams alone and in combination with either relebactam or vaborbactam against multidrug-resistant MABC clinical isolates. Our data demonstrate that both beta-lactamase inhibitors significantly improved the anti-MABC activity of many carbapenems (including imipenem and meropenem) and cephalosporins (including cefepime, ceftaroline, and cefuroxime). As a meropenem-vaborbactam combination is now marketed and an imipenem-relebactam combination is currently in phase III trials, these fixed combinations may become the beta-lactams of choice for the treatment of MABC infections. Furthermore, given the evolving interest in dual beta-lactam regimens, our results identify select cephalosporins, such as cefuroxime, with superior activity in the presence of a beta-lactamase inhibitor that are deserving of further evaluation in combination with these carbapenem-beta-lactamase inhibitor products.