Lateral dissemination and inter-patient transmission of blaKPC-3: role of a conjugative plasmid in spreading carbapenem resistance

The objective of this study was to describe the nosocomial spread of carbapenemase-producing enterobacteria and characterize a plasmid involved in KPC dissemination. Two Klebsiella pneumoniae, one Escherichia coli and one Citrobacter freundii isolated from two patients were studied. Susceptibility profiles were obtained using Etest. Carbapenemase activity was detected using the Carba NP test. beta-Lactamase gene content was screened by PCR and sequencing. K. pneumoniae isolates were genotyped by MLST and PFGE. KPC plasmid sizes were estimated by S1-DNA digestion and PFGE-Southern blot. Plasmids were sequenced using Illumina's technology and Sanger sequencing. Two patients sharing a room on a surgical unit were positive for carbapenemase-producing K. pneumoniae. One patient was also colonized with carbapenemase-producing C. freundii and E. coli. Neither patient had known risk factors for carbapenemase acquisition, although one patient had recent surgery at another Toronto hospital; the other patient's husband had surgery in New York City 3 years prior to her presentation. An extensive investigation was conducted at both hospitals, but no additional cases were identified. bla(KPC-3) was detected in all clinical isolates. Variable carbapenem resistance levels were observed. Both K. pneumoniae belonged to the same clone by PFGE and MLST (ST277). pKPC-SMH (similar to 53 kb) was identified in all the clinical isolates, showing identity only with structurally similar IncN plasmids. We describe intra- and inter-patient dissemination of bla(KPC). The involvement of a clone related to the successful K. pneumoniae ST258 and the bla(KPC-3) gene detected in an active Tn4401 transposon carried on a conjugative broad-host-range plasmid increased the potential for this horizontal transmission.