Durlobactam in combination with β-lactams to combat <i>Mycobacterium abscessus</i>
Eunjeong Shin, Khalid M Dousa, Magdalena A. Taracila, Christopher R. Bethel, Mary Nantongo, David C. Nguyen, Chidiebere Akusobi, Sebastian G. Kurz, Mark S. Plummer, Charles L. Daley, Steven M. Holland, Eric J. Rubin, Jürgen B. Bulitta, W. Henry Boom, Barry N. Kreiswirth, Robert A. Bonomo
Abstract
ABSTRACT Mycobacterium abscessus ( Mab ) presents significant clinical challenges. This study evaluated the synergistic effects of a β-lactam and β-lactamase inhibitor combination against Mab and explored the underlying mechanisms. Synergy was assessed through MIC tests and time-kill studies, and binding affinities of nine β-lactams and BLIs to eight target receptors (L,D-transpeptidases [LDT] 1–5, D,D-carboxypeptidase, penicillin-binding protein [PBP] B, and PBP-lipo) were assessed using mass spectrometry and kinetic studies. Thermal stability and morphological changes were determined. Imipenem demonstrated high binding affinity to LDTs and PBPs, with extremely low inhibition constants ( K i , app ; ≤0.002 mg/L for LDT1−2, ≤0.6 mg/L for PBPs), while cephalosporins, sulopenem, tebipenem, and amoxicillin exhibited moderate to low binding affinity. Durlobactam inactivated Bla Mab and LDT/PBPs more potently than avibactam. The K i,app s of durlobactam for PBP B, PBP-lipo, and LDT2 were below clinically achievable unbound concentrations, while avibactam’s K i,app for LDT/PBPs exceeded the clinical concentrations. Single β-lactam treatments resulted in minimal killing (~1 log 10 reduction). Although avibactam yielded no effect, combinations with avibactam showed a significant reduction (~4 log 10 CFU/mL). Durlobactam alone showed ~2 log 10 reduction, and when combined with imipenem or two β-lactams, durlobactam achieved near-eradication of Mab , surpassing the current therapy (amikacin + clarithromycin + imipenem/cefoxitin). Inactivation of PBP-lipo by sulopenem, imipenem, durlobactam, and amoxicillin (with avibactam) led to morphological changes, showing filaments. This study demonstrates the mechanistic basis of combinations therapy, particularly imipenem + durlobactam, in overcoming β-lactam resistance in Mab .