Dissemination of the bla_KPC gene by clonal spread and horizontal gene transfer: Comparative study of incidence and molecular mechanisms

Objectives: In addition to the global spread of the KPC-producing Klebsiella pneumoniae (KPC-KP) clonal complex (CC)-258 clone, the bla_KPC gene may also spread by horizontal gene transfer (HGT), as suspected when more than one KPC-producing Enterobacteriaceae (KPC-Ent) species are isolated in a single patient. We aimed to characterize the incidence and molecular features of KPC-KP that were isolated alone (singular KPC-KP) versus KPC-KP that were isolated together with another KPC-Ent species (joint KPC-KP). Methods: Isolates were collected from April 2011 to August 2012 at the Laniado Medical Center. Typing was done by CC-258 multiplex PCR and MLST. Plasmids were characterized by plasmid MLST (pMLST). The genetic environment of the bla_KPC gene was studied by sequencing. Results: During the 17 month period, there were 281 cases of singular KPC-KP and 8 cases of joint KPC-KP (P < 0.0001). Among the patients with joint KPC-KP, the additional KPC-Ent species were Escherichia coli (n = 6), Enterobacter aerogenes (n = 1), Enterobacter cloacae (n = 1) and Citrobacter freundii (n = 1). All singular KPC-KP isolates tested (n = 27) belonged to the CC-258 clone and carried the bla_KPC-3 allele, located inside a Tn4401a transposon. In contrast, joint KPC-KP/KPC-Ent isolates belonged to different STs and all but one carried the bla_KPC-2 allele. The bla_KPC-2 gene was located inside ΔTn4401c transposons that were harboured by IncN/pMLST ST-15-type plasmids possessing high conjugation efficiency. Conclusions: This study highlights two dissemination modes of the bla_KPC gene: Clonal spread of the CC-258 clone and, far less commonly, HGT-related spread, mediated by ST-15 plasmids that shuttle between a variety of species and clones.