Multiclonal spread of VIM-1-producing Enterobacter cloacae isolates associated with In624 and In488 integrons located in an IncHI2 plasmid

Over a 6-year period (2007–2012), the emergence of Enterobacter cloacae isolates resistant to β-lactams and with reduced susceptibility to carbapenems was observed in Hospital Universitario 12 de Octubre (Madrid, Spain). To determine the possible role of metallo-β-lactamases (MBLs) in the resistance profile of these isolates, a molecular and clinical epidemiological study was performed, including determination of patients’ clinical characteristics, genetic diversity of strains, resistance mechanisms to carbapenems, and the genetic environment of VIM-1. A total of 73 E. cloacae isolates showed resistance to extended-spectrum cephalosporins and reduced susceptibility to at least one carbapenem during 2007–2012. PCR amplification revealed the presence of blaVIM-1 gene in 37 isolates, blaVIM-2 in 1 isolate and blaKPC in 5 isolates. Molecular typing showed high clonal diversity of E. cloacae isolates carrying blaVIM-1. The genetic environment of blaVIM-1 was investigated and two integron structures were found: intI–blaVIM-1–aacA4–dfrB1–aadA1–catB2–qacEΔ1/sul1 (In624); and intI–blaVIM-1–aacA4–aadA1–qacEΔ1/sul1 (In488). Isolates belonging to three clones (A, F and G) harboured different types of integron (In624 or In488) despite belonging to the same clone. Conjugal experiments showed an association with a conjugative plasmid of ca. 300 kb belonging to IncHI2 group, which is common in Spanish hospitals, suggesting that the widespread dissemination of blaVIM-1 may be due to horizontal transfer of mobile genetic determinants rather than the result of spreading of a few clones. These results have implications for infection control programmes in the hospital.