Combinations comprising dual β-lactams and a β-lactamase inhibitor achieve optimal synergistic inhibition of Mycobacterium abscessus growth

Abstract

The historical model, which posits that {beta}-lactams inhibit bacterial growth while {beta}-lactamase inhibitors (BLIs) merely protect {beta}-lactams from enzymatic degradation, fails to fully explain their activity against Mycobacterium abscessus (Mab). This study demonstrates that synergistic effects extend beyond the traditional one {beta}-lactam+one BLI paradigm, refuting the oversimplified mechanistic framework. First, {beta}-lactam-based BLIs such as clavulanic acid, sulbactam, and tazobactam exhibit intrinsic antibacterial activity against Mab. These agents synergized not only with {beta}-lactams but also with one another, undermining their historical classification as mere {beta}-lactamase inhibitors. The data indicate that their activity is not limited to inhibiting {beta}-lactamases but extends to directly targeting critical bacterial processes. Second, dual {beta}-lactam combinations exhibit synergism against Mab even in the absence of BLIs. For example, despite being rapidly hydrolyzed by the native {beta}-lactamase BlaMab, amoxicillin demonstrates strong synergism with {beta}-lactams such as imipenem or ceftaroline. This suggests that the second {beta}-lactam either acts as a functional BLI surrogate or targets complementary pathways. Supporting this, experiments using penicillin- and carbapenem-based probes revealed that {beta}-lactams bind to multiple Mab proteins simultaneously, reinforcing the idea that their synergy arises from targeting complementary essential proteins. Finally, triple combinations comprising dual {beta}-lactam and one BLI, such as amoxicillin + ceftaroline + avibactam, achieved very high synergy, underscoring the complementary roles of dual {beta}-lactams and BLIs. The evidence in this study necessitates a revised model that can more accurately explain the activities of {beta}-lactams and BLIs and underscores the potential for optimizing {beta}-lactam/BLI regimens against Mab. IMPORTANCEThis research challenges old assumptions about how antibiotics fight bacteria, particularly Mycobacterium abscessus (Mab), a tough-to-treat infection. Traditionally, {beta}-lactam antibiotics were thought to stop bacterial growth, while {beta}-lactamase inhibitors (BLIs) just protected them from breakdown. However, this study reveals that BLIs like clavulanic acid can work together with another BLI or {beta}-lactam antibiotics for stronger effects. Surprisingly, even combinations comprising two BLIs can be highly effective, showing they target multiple critical bacterial processes simultaneously. Triple combinations--two {beta}-lactams and one BLI--proved especially powerful. These findings overturn outdated ideas, offering a smarter way to use these drugs to combat difficult infections and save lives.