An unusual occurrence of plasmid-mediated blaOXA-23 carbapenemase in clinical isolates of Escherichia coli from India

Abstract

The bla_OXA-23 group was considered as the first group of OXA-type β-lactamases conferring carbapenem resistance and has been reported worldwide in Acinetobacter baumannii, however their presence in Escherichia coli is very rare and unique. This study describes an unusual occurrence of bla_OXA-23 in 14 clinical isolates of E. coli obtained from intensive care unit patients admitted to a tertiary referral hospital in India. The bla_OXA-23 gene was found located within a self-conjugative plasmid of IncF_repB and IncK incompatibility types and simultaneously carrying bla_CTX-M-15, bla_VEB-1, bla_PER-1 and/or bla_NDM-1. The copy number of bla_OXA-23 within the IncK-type plasmid was inversely proportional to increasing concentrations of imipenem, whereas in the case of the IncF_repB-type the result was variable; and increased copy number of the IncK-type plasmid was observed with increasing concentrations of meropenem. Plasmids encoding bla_OXA-23 could be successfully eliminated after single treatment and were found to be not highly stable, as complete loss of plasmids was observed within 5-10 days. This study emphasises that carbapenem stress invariably altered the copy number of two different Inc type plasmids encoding the bla_OXA-23 resistance gene and also highlights a potential threat of clonal expansion of this class D carbapenemase through a heterologous host in this country, which is in second incidence globally.

Keywords: Escherichia coli; ICU; Stability; bla(OXA-23).