Characterisation of the CTX-M-15-encoding gene in Klebsiella pneumoniae strains from the Barcelona metropolitan area: plasmid diversity and chromosomal integration

Abstract

The localisation and genetic organisation of bla CTX-M-15 were studied in 37 CTX-M-15-producing Klebsiella pneumoniae isolates collected from 2005 to 2008 within the Barcelona metropolitan area. Polymerase chain reaction (PCR)-based replicon typing and Southern hybridisations were used to identify the bla CTX-M-15 location. The genetic environment was analysed by PCR mapping and sequencing, and transferability of bla CTX-M-15 was evaluated by conjugation and transformation assays. The majority of the 37 isolates carried bla CTX-M-15 in a plasmid location, frequently associated with the aac(6′)-Ib-cr gene. Plasmids encoding bla CTX-M-15 carried three distinct replicons, i.e. IncFII, IncR and IncFIIk, the latter two not having been described previously in association with bla CTX-M-15. Several of these plasmids were not self-transferable. Furthermore, in all isolates belonging to sequence type ST-1, bla CTX-M-15 was found integrated into the K. pneumoniae chromosome. In all the studied isolates, the mobile element IS Ecp1 was found upstream of bla CTX-M-15, whereas IS 26 was found inserted within IS Ecp1 in several isolates, in previously unreported positions. In conclusion, these findings indicate that among K. pneumoniae strains isolated in the Barcelona metropolitan area, bla CTX-M-15 is associated with diverse genetic elements, including the IncR and IncFIIk replicons, as reported for the first time here, and the chromosome.