Phenotypic Characterization of OXA-439, an OXA-163 variant, isolated from uropathogenic Escherichia coli
Year: 2026
Type: preprint
Abstract: OXA-48-like β-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 β-lactam/β-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 ± 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.
Institution: Institut Pasteur de Montevideo
Language: English
Subfield: Molecular Medicine
Domain: Life Sciences
Open Access status: green
Award: G4870198231
OpenAlex ID: W7213331338