Phenotypic Characterization of OXA-439, an OXA-163 variant, isolated from uropathogenic Escherichia coli

OXA-48-like {beta}-lactamases, such as OXA-163, OXA-181, OXA-405, OXA-505, among others, are class D carbapenem-hydrolyzing enzymes increasingly reported worldwide, yet some variants remain poorly characterized at the phenotypic levels. Here, we report OXA-439, a variant of OXA-163, in a producing uropathogenic Escherichia coli (UPEC) in Uruguay, recovered from a catheter-associated urinary tract infection with discordant routine susceptibility results. The specific contribution of OXA-439, bla-OXA-48, bla-OXA-163, and bla-OXA-439 were cloned into pET24a vector and expressed in Escherichia coli BL21(DE3), and their activity was evaluated by MIC microdilution against a panel of penicillins, ESCs, carbapenems, and {beta}-lactam/{beta}-lactamase inhibitor combinations. OXA-439 exhibited a substrate profile highly similar to OXA-163 conferring resistance to piperacillin and third-generation cephalosporins while remaining susceptible to carbapenems but with globally reduced MIC values and a complete loss of activity toward amoxicillin and clavulanate. These data suggest that the Y123H substitution, located near the catalytic Ser70/Lys73 region, subtly perturbs the active-site environment and decreases penicillinase efficiency.