Reduced ceftazidime and ertapenem susceptibility due to production of OXA-2 in Klebsiella pneumoniae ST258

Background: OXA-2 is a class D b-lactamase that confers resistance to penicillins, as well as narrow-spectrum cephalosporins. OXA-2 was recently reported to also possess carbapenem-hydrolysing activity. Here, we describe a KPC-2-encoding Klebsiella pneumoniae isolate that demonstrated reduced susceptibility to ceftazidime and ertapenem due to production of OXA-2. Objectives: To elucidate the role of OXA-2 production in reduced ceftazidime and ertapenem susceptibility in a K. pneumoniae ST258 clinical isolate. Methods: MICs were determined by the agar dilution method. WGS was conducted to identify and compare resistance genes between isolates. Expression of KPC-2 was quantified by quantitative RT–PCR and immunoblotting. OXA-2 was expressed in Escherichia coli TOP10, as well as in K. pneumoniae ATCC 13883, to define the relative contribution of OXA-2 in b-lactam resistance. Kinetic studies were conducted using purified OXA-2 enzyme. Results: K. pneumoniae 1761 belonged to ST258 and carried both bla_KPC-2 and bla_OXA-2. However, expression of bla_KPC-2 was substantially reduced due to an IS1294 insertion in the promoter region. K. pneumoniae 1761, K. pneumoniae ATCC 13883 and E. coli TOP10 carrying bla_OXA-2-harbouring plasmids showed reduced susceptibility to ertapenem and ceftazidime, but meropenem, imipenem and cefepime were unaffected. bla_OXA-2 was carried on a 2910 bp partial class 1 integron containing aacA4-bla_OXA-2-qacED1-sul1 on an IncA/C₂ plasmid, which was not present in the earlier ST258 isolates possessing bla_KPC-2 with intact promoters. Hydrolysis of ertapenem by OXA-2 was confirmed using purified enzyme. Conclusions: Production of OXA-2 was associated with reduced ceftazidime and ertapenem susceptibility in a K. pneumoniae ST258 isolate.