Characterization of CTX-M-producing Escherichia coli by repetitive sequence-based PCR and real-time PCR-based replicon typing of CTX-M-15 plasmids

The emergence of extended-spectrum -lactamase (ESBL)-producing Enterobacteriaceae is a major global concern. CTX-M is the dominating ESBL type worldwide, and CTX-M-15 is the most widespread CTX-M type. The dissemination of CTX-M appears to be in part due to global spread of the Escherichia coli clone O25b-ST131. However, the gene-encoding CTX-M is mainly located on mobile genetic elements, such as plasmids, that also promote the horizontal dissemination of the CTX-M genes. In this study, 152 CTX-M-producing E. coli isolated in 1999-2008 in orebro County, Sweden, were typed using a commercial repetitive sequence-based PCR (the DiversiLab system), and the prevalence of ST131 was investigated by pabB PCR. Real-time PCR-based plasmid replicon typing was performed on 82 CTX-M-15-producing E. coli isolates. In general, the CTX-M-producing E. coli population was genetically diverse; however, ST131 was highly prevalent (27%), and the dominating clone in our area. The bla(CTX-M-15) gene was mainly located on IncF plasmids (69%), but a relatively high proportion of IncI1 plasmids (29%) were also detected among E. coli with diverse rep-PCR patterns, indicating that horizontal transmission of IncI1 plasmids carrying bla(CTX-M-15) may have occurred between different E. coli strains.