Prevalence of SXT/R391-like integrative and conjugative elements carrying blaCMY-2 in Proteus mirabilis

Objectives: To characterize the vectors involved in the dissemination of blaCMY-2 genes in clinical isolates of Proteus mirabilis collected between 1999 and 2007. Methods: Plasmid analysis of 19 P. mirabilis carrying ampC genes was performed by PCR-based replicon typing, S1-PFGE and Southern hybridization with ampC and replicon probes. Isolates that could not be characterized were examined for the presence of SXT/R391-like elements. To demonstrate the involvement of these elements in the dissemination of blaCMY-2, we performed a PCR amplification of the integrase (int) and toxin/antitoxin (TA) genes from SXT/R391-like integrative conjugative elements (ICEs). Later on, I-Ceu-I PFGE gels and hybridization with blaCMY-2, int and prfC probes were performed. The genetic organization of blaCMY-2 was also studied. Results: ampC genes were located on large conjugative plasmids in 11 of the 19 (58%) P. mirabilis studied. However, in eight of these isolates a plasmid was not involved in the mobilization of ampC genes. I-Ceu-I PFGE and hybridization analyses revealed that blaCMY-2 were chromosomally located in these eight P. mirabilis isolates. The genetic organization of blaCMY-2 and hybridization analyses revealed that blaCMY-2 was carried by an ICE almost identical to ICEPmiJpan1 in seven out of these eight isolates. Conclusions: The prevalence of ICEs carrying blaCMY-2 was surprisingly high [37% (7 out of 19)]. This is the first study giving prevalence data on ICEs carrying blaCMY-2 genes. These results suggest the need to study these mobile genetic elements in the context of dissemination of acquired AmpC β-lactamases and also of other β-lactamases, such as extended-spectrum β-lactamases and carbapenemases.