Long-distance transmission of tmexCD1-toprJ1 positive Klebsiella pneumoniae between humans and food animals.

Objectives: The tmexCD1-toprJ1 RND efflux pump gene cluster is predominantly identified among Klebsiella pneumoniae (Kp) from humans and food animals. However, the mechanism of the long and rapid dissemination of such resistance determinant among strains from humans, food animals and the environment is unclear.

Methods: Kp isolates were collected from two surveillance projects among patients and food animals. Whole-genome sequencing for phylogenetically close-related tmexCD1-toprJ1-positive and negative isolates, and phylogenic, plasmid stability and fitness cost analyses were performed.

Results: Among 2592 clinical Kp isolates and 243 Kp isolates from food animals, the minimum inhibitory concentrations of tigecycline were 2 to 32 mg/L. The tmexCD1-toprJ1-positive isolates belonged to five sequence types (STs) and exhibited tigecycline resistance. By phylogenetic analyses, we have shown that tmexCD1-toprJ1-positive ST22 may have derived from tmexCD1-toprJ1-negative isolates in our hospital, whereas tmexCD1-toprJ1-positive ST726 showed a long-distance transmission among human and food animals. Different types of plasmids harboring tmexCD1-toprJ1 were identified, which have been disseminated among bacteria from humans, food animals and the environment. Interestingly, low fitness costs of the tmexCD1-torpJ1-positive isolates compared to the phylogenetically close tmexCD1-toprJ1-negative isolates.

Conclusions: The long and rapid transmission of tmexCD1-toprJ1 was predominantly caused by plasmids. In One Health, systematic surveillance and studies of isolates from different sources, are urgently needed to understand the mechanism of resistance genes dissemination.