Emergence of carbapenem-resistant and clinical isolates with plasmids harbouring in Japan.

The emergence of carbapenem-resistant species producing metallo-β-lactamase (MBL) has become a serious medical problem worldwide. IMP-type MBL was firstly detected in 1991 in Japan. Since then, it has become one of the most prevalent types of MBLs. Avirulent species of , such as , function as reservoirs of drug resistance-associated genes encoding carbapenemases in clinical settings. Active surveillance for carbapenem-resistant Gram-negative pathogens was conducted in 2019 at a hospital in Tokyo, Japan. Of the 543 samples screened for carbapenem-resistant isolates, 2 were species of . One was from a stool sample from a medical staff member, and the other was from a stool sample from a hospitalized patient. Whole-genome sequencing showed that the former isolate was a strain of , and the latter was a strain of , a species close to . Both isolates were resistant to all carbapenems and harboured genes encoding IMP-1 MBL, which conferred resistance to carbapenems. The genes of and were located on the plasmids, pMRCP2, 323125 bp in size, and pMRCP1333, 16592 bp in size, respectively. The sequence of 82 % of pMRCP2 was 92 % similar to the sequence of a plasmid of PA83, whereas the sequence of 79 % of pMRCP1333 was >95 % similar to the sequence of a plasmid of FDAARGOS 162. The genomic environments surrounding the of pMRCP2 and pMRCP1333 differed completely from each other. These results indicate that the two isolates acquired from different sources and that and function as vectors and reservoirs of carbapenem-resistant genes in hospitals.