FRI-4 carbapenemase-producing Enterobacter cloacae complex isolated in Tokyo, Japan

Objectives: A carbapenem-resistant Enterobacter cloacae complex isolated in Tokyo, Japan, produced a carbapenemase that was detected by a Carba NP test and a modified carbapenem inactivation method, but none of the 'Big Five' carbapenemase genes was detected by PCR. This study aimed to identify the carbapenemase. Methods: Carbapenemase genes were screened by WGS. Next, we generated a recombinant plasmid in which the carbapenemase gene was inserted. We also extracted the carbapenemase gene-carrying plasmid from the E. cloacae complex. The effects of both plasmids on the antibiotic susceptibility of Escherichia coli were then tested. The carbapenemase gene-carrying plasmid in the E. cloacae complex was completely sequenced. Results: A novel carbapenemase gene, bla(FRI-4), encoded an amino acid sequence that was 93.2% identical to French imipenemase (FRI-1). E. coli transformed with bla(FRI-4) showed reduced carbapenem susceptibility. A complete sequence of the bla(FRI-4)-carrying 98 508 bp IncFII/IncR plasmid (pTMTA61661) showed that bla(FRI-4) and the surrounding region (18.7 kb) were duplicated. Conclusions: The FRI-4-producing E. cloacae complex was isolated in Japan, whereas all other FRI variants have been found in Europe, suggesting that the spread of FRI carbapenemases is global.