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

Resistance to antipseudomonal penicillins and cephalosporins is often driven by the overproduction of the intrinsic beta-lactamase AmpC. However, OXA-10-family beta-lactamases are a rich source of resistance in Pseudomonas aeruginosa. OXA beta-lactamases have a propensity for mutation that leads to extended spectrum cephalosporinase and carbapenemase activity. In this study, we identified isolates from a subclade of the multidrug-resistant (MDR) high risk P. aeruginosa clonal complex CC446 with a resistance to ceftazidime. A genomic analysis revealed that these isolates harbored a plasmid containing a novel allele of bla(OX)(A-10), named bla(OX)(A-935), which was predicted to produce an OXA-10 variant with two amino acid substitutions: an aspartic acid instead of a glycine at position 157 and a serine instead of a phenylalanine at position 153. The G157D mutation, present in OXA-14, is associated with the resistance of P. aeruginosa to ceftazidime. Compared to OXA-14, OXA-935 showed increased catalytic efficiency for ceftazidime. The deletion of bla(OXA-9)(35) restored the sensitivity to ceftazidime, and susceptibility profiling of P. aeruginosa laboratory strains expressing bla(OX)(A-)(935) revealed that OXA-935 conferred ceftazidime resistance. To better understand the impacts of the variant amino acids, we determined the crystal structures of OXA-14 and OXA-935. Compared to OXA-14, the F153S mutation in OXA-935 conferred increased flexibility in the omega (Omega) loop. Amino acid changes that confer extended spectrum cephalosporinase activity to OXA-10-family ,beta-lactamases are concerning, given the rising reliance on novel beta-lactam/beta-lactamase inhibitor combinations, such as ceftolozane-tazobactam and ceftazidime-avibactam, to treat MDR P. aeruginosa infections.

Automated summary

Resistance to antipseudomonal penicillins and cephalosporins in Pseudomonas aeruginosa is often driven by the overproduction of AmpC beta-lactamase and OXA-10-family beta-lactamases. This study identified a novel allele of bla(OX)(A-10), named bla(OX)(A-935), which confers ceftazidime resistance and showed increased catalytic efficiency for ceftazidime compared to OXA-14. Crystal structures of OXA-14 and OXA-935 revealed that the F153S mutation in OXA-935 increases flexibility in the omega loop. Considering the reliance on novel beta-lactam/beta-lactamase inhibitor combinations, the amino acid changes in OXA-10-family beta-lactamases are of concern.