Citrobacter freundii carrying bla KPC-2 and bla NDM-1: Characterization by whole genome sequencing

Abstract

A carbapenem-resistant Citrobacter freundii strain WCHCF65 was recovered from hospital sewage and was characterized by genome sequencing and conjugation experiments. The strain carried nine genes encoding β-lactamases including two carbapenemase genes, bla NDM-1 and bla KPC-2. bla NDM-1 was carried on an IncX3 plasmid, which was identical to a plasmid found in a local Escherichia coli, suggesting interspecies horizontal transfer. bla KPC-2 was bracketed by two copies of insertion sequence ISKpn19, which could form a composite transposon with the potential to mobilize bla KPC-2, on a new type of plasmid. The coexistence of bla NDM-1 and bla KPC-2 conferred higher levels of resistance to carbapenems compared with bla NDM-1 or bla KPC-2 alone. The coexistence of these carbapenemase genes, on two different plasmids, in one strain may allow new genetic platforms to be generated to mediate their spread.