Molecular characterization of IMP-1-producing Enterobacter cloacae complex isolates in Tokyo [PublishAheadOfPrint]

Although KPC enzymes are most common among carbapenemases produced by Enterobacter cloacae complex globally, the epidemiology varies from one country to another. While previous studies have suggested that IMP enzymes are most common in Japan, detailed analysis has been scarce thus far. Here we carried out a molecular epidemiological study and plasmid analysis of IMP-1-producing E. cloacae complex isolates collected from 3 hospitals in central Tokyo using whole genome sequencing. Seventy-one isolates were classified into several STs and 49 isolates were identified as Enterobacter hormaechei ST78. Isolates of ST78 were divided into 3 clades by Core-genome SNPs-based phylogenetic analysis. Whereas isolates of clade 3 were isolated only from one hospital, isolates of clade 1 and 2 were identified from multiple hospitals. Ten of 12 clade 1 isolates and one of four clade 2 isolates carried bla_IMP-1 on IncHI2 plasmids with high similarity of genetic structures. In addition, these plasmids shared backbone structure with IncHI2 plasmids carrying bla_IMP reported from other countries of the Asia-Pacific Region. All isolates of clade 3 except one carried bla_IMP-1 in In1426 on IncW plasmids. An isolate of clade 3, which lacked IncW plasmids, carried bla_IMP-1 in In1426 on an IncFIB plasmid. These observations suggest that IMP-producing E. cloacae complex isolates with a diversity of host genomic backgrounds have spread in central Tokyo and the possible contribution of IncHI2 plasmids towards this phenomenon.

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