Emergence of the mobile RND-type efflux pump gene cluster tmexCD1-toprJ1 in Klebsiella pneumoniae clinical isolates in Japan

Abstract Background Tigecycline is an antimicrobial agent with a broad spectrum of activity against both Gram-positive and Gram-negative bacteria. However, mobile tigecycline resistance gene clusters, such as tnfxB-tmexCD-toprJ, have spread globally. The prevalence of tigecycline-resistant Enterobacterales in clinical settings in Japan is unknown. Objectives To investigate the tnfxB-tmexCD-toprJ gene cluster in the genome sequences of Enterobacterales clinical isolates in Japan. Methods We investigated the tnfxB-tmexCD-toprJ cluster from the genome sequences of 5143 Enterobacterales isolates collected from 175 hospitals around Japan between 2019 and 2020 as part of a national genomic surveillance program for antimicrobial-resistant bacteria. Results The tnfxB1-tmexCD1-toprJ1 cluster was detected in two Klebsiella pneumoniae isolates in 2019. One isolate possessed a 299.4 kb IncFIB(K) plasmid, pJBBGAAF19431, and the other possessed a 224.9 kb IncHI1B/IncFIB(K) hybrid plasmid, pJBEAACG19501, co-carrying multiple antimicrobial resistance genes, including extended-spectrum β-lactamase genes, blaOXA-1 and blaCTX-M-27, respectively, along with tnfxB1-tmexCD1-toprJ1. The genetic context of the tnfxB1-tmexCD1-toprJ1-surrounding structure on pJBBGAAF19431 was similar to that of a K. pneumoniae plasmid pHNAH8I-1 from a chicken in China in 2017, and the cluster was embedded in an apparently intact mobile DNA element: strand-biased circularizing integrative element. The tnfxB1-tmexCD1-toprJ1 on pJBEAACG19501 was embedded in a Tn3 family transposon related to TnAs1. The plasmid pJBEAACG19501 was highly similar to that of K. pneumoniae, isolated from humans in China in 2021. Conclusions tmexCD-toprJ was present in Japan as of 2019. Even in Japan, where the clinical use of tigecycline is significantly rare, tmexCD-toprJ-harbouring multidrug-resistant Enterobacterales is a public health threat and requires continuous monitoring.