OXA-163, an OXA-48-related class D β-lactamase with extended activity toward expanded-spectrum cephalosporins.

Two bla(OXA-48)-like-positive isolates (Klebsiella pneumoniae and Enterobacter cloacae) were recovered in Argentina in 2008 as part of a large-scale survey focused on multidrug resistance in Enterobacteriaceae. In both cases, sequencing identified β-lactamase OXA-163, differing from OXA-48 by a single amino substitution and a 4-amino-acid deletion. OXA-163 hydrolyzed penicillins, ceftazidime, and cefotaxime, whereas OXA-48 did not. However, OXA-163 had a much lower ability to hydrolyze carbapenems than OXA-48, therefore barely being considered a carbapenemase. In both isolates, the bla(OXA-163) gene was located on plasmids that differed in structure and size. However, a detailed genetic analysis revealed a similar genetic context in those isolates, with the bla(OXA-163) gene being bracketed by novel transposase genes, making this genetic environment different from that reported for the bla(OXA-48) gene. This study identified the first class D β-lactamase compromising both extended-spectrum cephalosporin and carbapenem activities.