Mycobacterium abscessus (Mab) causes serious infections that often require over 18 months of antibiotic combination therapy. There is no standard regimen for the treatment of Mab infections and the multitude of combinations that have been used clinically have had low success rates and high rates for toxicities. With β-lactam antibiotics being safe, double β-lactam and β-lactam/β-lactamase inhibitor combinations are of interest for improving treatment of Mab infections and minim izing toxicity. However, a mechanistic approach for building these combinations is lacking since little is known about which penicillin-binding protein (PBP) target receptors are inactivated by different β-lactams in Mab. We determined the preferred PBP targets of 13 β-lactams and two β-lactamase inhibitors in two Mab strains and identified PBP sequences by proteomics. The Bocillin FL binding assay was used to determine the β-lactam concentrations (IC50) that half-maximally inhibited Bocillin binding. Principal component analysis identified four clusters of PBP occupancy patterns. Carbapenems inactivated all PBPs at low concentrations (0.016-0.5mg/L; cluster 1). Cephalosporins (cluster 2) inactivated PonA2, PonA1, and PbpA at low (0.031-1mg/L; ceftriaxone and cefotaxime) or intermediate concentrations (0.35-16mg/L; ceftazidime and cefoxitin). Sulbactam, aztreonam, carumonam, mecillinam and avibactam (cluster 3) inactivated the same PBPs as cephalosporins , but required higher concentrations. Other penicillins (cluster 4) specifically targeted PbpA at 2-16mg/L. Carbapenems, ceftriaxone and cefotaxime were the most promising β-lactams since they inactivated most or all PBPs at clinically relevant concentrations. These first PBP occupancy patterns in Mab provide a mechanistic foundation for selecting and optimizing safe and effective combination therapies with β-lactams.
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