Emergence of a novel mobile RND-type efflux pump gene cluster, tmexC3D2-toprJ1b, in Pseudomonas species

Tigecycline exhibits promising activity against multidrug-resistant Gram-negative bacteria (MDR-GNB), whose infections are difficult to treat with antimicrobials. However, mobile tigecycline resistance genes, such as tmexCD-toprJ , have emerged in Enterobacterales isolated in China, Vietnam, and possibly other countries in the world. In this study, we investigated tigecycline-nonsusceptible GNB in Japan. Eight tigecycline- and carbapenem-nonsusceptible isolates of Pseudomonas alcaligenes were obtained from sewage water from a medical institution in Japan in 2020. Whole genome analysis of all P. alcaligenes isolates was performed using short-read sequencing, and the isolate KAM426 was further analyzed using long-read sequencing. For important antimicrobial resistance genes, analysis of surrounding structures and comparison with similar sequences in the public genome database were performed. We identified a novel hybrid type of tmexCD-toprJ gene cluster, tmexC3D2-toprJ1b consisting of tmexC3 , tmexC2 , and toprJ1b , in phylogenetically clonal isolates of P. alcaligenes . The complete genome sequence of KAM426 revealed that this isolate co-harbors tmexC3D2-toprJ1b and two copies of the carbapenemase gene bla IMP-1 on the chromosome. tmexC3D2-toprJ1b in KAM426 was flanked by the IS 5 /IS 1182 family transposase gene, suggesting that the gene cluster was acquired by horizontal gene transfer (HGT). tmexC3D2-toprJ1b seemed to have spread to other Pseudomonas species such as Pseudomonas aeruginosa via HGT mediated by mobile gene elements such as a plasmid. This study identified tmexCD-toprJ -like tigecycline resistance genes in Japan for the first time and suggests that diverse tmexCD-toprJ -like gene clusters, including tmexC3D2-toprJ1b , have spread among MDR-GNB worldwide. Further epidemiological genomic studies in clinical and environmental settings are needed. ### Competing Interest Statement The authors have declared no competing interest.