Burkholderia pseudomallei PenI β-lactamase and variants are potently inhibited by taniborbactam

Burkholderia pseudomallei is a Gram-negative pathogen that causes melioidosis, a severe and often fatal disease. Due to its recognized potential as a bioterrorism agent, it is critical that appropriate antimicrobial agents are available for post-exposure prophylaxis and treatment of melioidosis. Cefepime-taniborbactam is a novel β-lactam-β-lactamase inhibitor combination in clinical development, with promising activity against Gram-negative bacteria producing class A, B, C, and/or D β-lactamases. Herein, we demonstrate the inhibitory activity of taniborbactam against PenI, the class A β-lactamase produced by B. pseudomallei. Isogenic Escherichia coli strains producing PenI and its ceftazidime-resistance-conferring variants (C69Y and P167S) showed ceftazidime minimum inhibitory concentration (MIC) of 64 mg/L for the strain producing PenI and 1,024 mg/L for the strains producing the variants, whereas cefepime MIC was 128-256 mg/L for these three strains. While the addition of avibactam decreased ceftazidime MIC to 1 mg/L for PenI and 8-16 mg/L for the variants, the addition of taniborbactam decreased cefepime MIC to ≤0.5 mg/L for PenI and the variants. Similarly, an 8-fold reduction of the cefepime MIC upon addition of taniborbactam was observed in an avirulent B. pseudomallei strain. Furthermore, taniborbactam inhibited PenI and its C69Y variant with an apparent K_i of 0.11 and 3.1 µM, respectively. Lastly, co-crystallography and molecular dynamics simulations showed that taniborbactam induced the formation of a disulfide bond between Cys77 and Cys123, which destabilizes the deacylation water and strengthens the taniborbactam-PenI complex. These results support the development of cefepime-taniborbactam as a promising agent for the treatment of infections by B. pseudomallei.