Comparison of two carbapenem-resistant Klebsiella pneumoniae clones: from a contained outbreak in a paediatric population and from a national epidemic

A refractory epidemic of carbapenem-resistant Klebsiella pneumoniae (CRKP) emerged in the adult population at our hospital in 2005, as in most Israeli hospitals. Contemporaneously, a different clone of CRKP caused an easily contained outbreak in a paediatric long-term care facility (LTCF) in Jerusalem. While previously identified host-related risk factors for colonization by these organisms undoubtedly contributed to these outbreaks, it is very likely that bacterial factors might be crucial in explaining the striking differences in transmissibility between the implicated strains. We therefore sought bacterial factors associated with these different epidemiological behaviours. Seven CRKP isolated at our hospital and the LTCF during 200809 were examined by antimicrobial susceptibility testing and PFGE, and further analyses of these two clones was done using multilocus sequence typing and competition experiments. Plasmids were analysed by conjugation, restriction mapping, PCR and sequencing. Both clones were multidrug resistant and harboured identical plasmids carrying the bla(KPC-3) gene. The hyper-transmissible epidemic clone carried additional antibiotic resistance genes and hosted an additional plasmid. The clone from the LTCF did not demonstrate hyper-transmissible properties despite its presence in an institution of a type commonly plagued by the epidemic clone. Competition assays showed the more easily contained strain to be fitter. These findings suggest that neither the presence of the plasmid carrying the bla(KPC-3) gene nor relative survival fitness account for the hyper-transmissibility of the epidemic strain. The role of patient age in susceptibility to colonization by the epidemic strain should be investigated.