Emergence of Tigecycline‐Resistant <i>Pseudomonas aeruginosa</i> Harbouring <i>tmexC6D6</i> ‐ <i>toprJ1b</i> From Hospital Sewage in Japan

The mobile tmexCD-toprJ gene clusters encode resistance-nodulation-division (RND)-type multidrug efflux pumps which confer resistance to multiple antimicrobials, including tigecycline. Here we report the first identification of tmexCD-toprJ-harbouring Pseudomonas aeruginosa strain KAM950, isolated from hospital sewage in Japan in 2022. The isolate exhibited reduced susceptibility to tigecycline and carbapenems. Complete genome sequence analysis showed that KAM950 belongs to sequence type 244 (ST244) according to multilocus sequence typing, an internationally recognised epidemic clone, and harbours multiple antimicrobial resistance genes, including the tmexCD-toprJ variant, tmexC6D6-toprJ1b. Notably, the tmexC6D6-toprJ1b gene cluster was located on the chromosome, adjacent to the transcriptional regulator gene tnfxB6 and an IS5/IS1182 family transposase gene. Furthermore, an IS4-mediated disruption of the porin gene oprD was observed, potentially contributing to carbapenem resistance. BLASTn analysis revealed that the IS5/IS1182-tnfxB6-tmexC6D6-toprJ1b gene cluster present in both chromosomal and plasmid sequences among the order Pseudomonadaceae, indicating potential horizontal gene transfer of tnfxB6-tmexC6D6-toprJ1b mediated by IS5/IS1182. Our findings highlight the ongoing expansion of variant diversity and geographic spread of tmexCD-toprJ-like gene clusters, and underscore the importance of genomic surveillance for emerging antimicrobial resistance determinants in both clinical and environmental settings.