First identification of an IMI-1 carbapenemase-producing colistin-resistant Enterobacter cloacae in China

Background: Carbapenem resistance among the Enterobacteriaceae is a serious healthcare challenge. bla(IMI) is a carbapenemase gene mediating resistance to carbapenems but has not been commonly found. A bla(IMI)-carrying Enterobacter cloacae, which was also resistant to colistin, is reported here. Findings: E. cloacae strain WCHECl-1060 was recovered from a blood sample of a leukemia patient, who was not previously exposed to colistin. Strain WCHECl-1060 belongs to a new sequence type, ST410, and was resistant to carbapenems and colistin but was susceptible to third-generation cephalosporins. A new allelic variant of bla(IMI)-1, which has two silent mutations compared to the original bla(IMI)-1 variant, was found in strain WCHECl-1060. Conjugation and transformation experiments failed to transfer bla(IMI)-1, suggesting a likely chromosome origin. Conclusions: To our knowledge, this is the first report of an IMI-1 carbapenemase-producing colistin-resistant E. cloacae in China. Microbiological laboratories should be aware of the unusual carbapenem-resistant but third-generation cephalosporin-susceptible profiles of these IMI-producing isolates. The trend of colistin resistance among the Enterobacteriaceae should be also monitored.