OXA-163, an OXA-48-Related Class D β-Lactamase with Extended Activity Toward Expanded-Spectrum Cephalosporins

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Abstract
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.

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