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

To characterize the vectors involved in the dissemination of bla(CMY-2) genes in clinical isolates of Proteus mirabilis collected between 1999 and 2007.

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 bla(CMY-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 bla(CMY-2), int and prfC probes were performed. The genetic organization of bla(CMY-2) was also studied.

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 bla(CMY-2) were chromosomally located in these eight P. mirabilis isolates. The genetic organization of bla(CMY-2) and hybridization analyses revealed that bla(CMY-2) was carried by an ICE almost identical to ICEPmiJpan1 in seven out of these eight isolates.

The prevalence of ICEs carrying bla(CMY-2) was surprisingly high [37% (7 out of 19)]. This is the first study giving prevalence data on ICEs carrying bla(CMY-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.