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Updated: Feb 7, 2026

Generation of Enterobacter sp. YSU Auxotrophs Using Transposon Mutagenesis
Published on: October 31, 2014
FRI-4 carbapenemase-producing Enterobacter cloacae complex isolated in Tokyo, Japan
Hiroaki Kubota1, Yoshifumi Uwamino2,3, Mari Matsui4
1Department of Microbiology, Tokyo Metropolitan Institute of Public Health, 3-24-1 Hyakunincho, Shinjuku-ku, 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, blaFRI-4, encoded an amino acid sequence that was 93.2% identical to French imipenemase (FRI-1). E. coli transformed with blaFRI-4 showed reduced carbapenem susceptibility. A complete sequence of the blaFRI-4-carrying 98 508 bp IncFII/IncR plasmid (pTMTA61661) showed that blaFRI-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.
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