Functional and Structural Characterization of OXA-935, a Novel OXA-10-family β-lactamase from Pseudomonas aeruginosa

ABSTRACT Resistance to antipseudomonal penicillins and cephalosporins is often driven by the overproduction of the intrinsic β-lactamase AmpC. However, OXA-10-family β-lactamases are a rich source of resistance in Pseudomonas aeruginosa . OXA β-lactamases have a propensity for mutation leading to extended spectrum cephalosporinase and carbapenemase activity. In this study, we identified isolates from a subclade of the multidrug-resistant (MDR) high risk clonal complex CC446 with resistance to ceftazidime. Genomic analysis revealed that these isolates harbored a plasmid containing a novel allele of bla OXA-10 , named bla OXA-935 , which was predicted to produce an OXA-10 variant with two amino acid substitutions: an aspartic acid instead of glycine at position 157 and a serine instead of phenylalanine at position 153. The G157D mutation, present in OXA-14, is associated with resistance to ceftazidime. Deletion of bla OXA-935 restored sensitivity to ceftazidime and susceptibility profiling of P. aeruginosa laboratory strains expressing bla OXA-935 revealed that OXA-935 conferred ceftazidime resistance. To better understand the impact of the variant amino acids, we determined the crystal structures of OXA-14 and OXA-935. In OXA-14, one of two monomers contained the canonical carbamylated lysine-70 (K70). In contrast, both monomers of OXA-935 were decarbamylated at K70, and the F153S mutation conferred increased flexibility to the omega (Ω) loop. Compared to OXA-14, the catalytic efficiency of OXA-935 for nitrocefin was significantly reduced. Amino acid changes that confer extended spectrum cephalosporinase activity to OXA-10-family β-lactamases are concerning given rising reliance on novel β-lactam/β-lactamase inhibitor combinations such as ceftolozane-tazobactam and ceftazidime-avibactam to treat MDR P. aeruginosa infections.