Plasmids Shape the Current Prevalence of tmexCD1-toprJ1 among Klebsiella pneumoniae in Food Production Chains

The emergence of novel antimicrobial resistance genes conferring resistance to last-resort antimicrobials poses a serious challenge to global public health security. Recently, one plasmid-mediated RND family multidrug resistance efflux pump gene cluster named tmexCD1-toprJ1, which confers resistance to tigecycline, was identified in bacteria of animal and human origins. However, the comprehensive landscape of the genomic epidemiology of this novel resistance determinant remained unclear. To fill this knowledge gap, we isolated 25 tmexCD1-toprJ1-positive bacteria from 682 samples collected along the pork production chain, including swine farms, slaughterhouses, and retail pork, and characterized the positive strains systematically using antimicrobial susceptibility testing, conjugation assays, single-molecule sequencing, and genomic analyses. We found that tmexCD1-toprJ1-positive bacteria were most prevalent in slaughterhouses (7.32%), followed by retail pork (0.72%). Most of the positive strains were Klebsiella pneumoniae (23/25), followed by Proteus mirabilis (2/25). IncFIB(Mar)/IncHI1B hybrid plasmids were mainly vectors for tmexCD1-toprJ1 and dominated the horizontal dissemination of tmexCD1-toprJ1 among K. pneumoniae isolates. However, in this study, we identified the IncR plasmid as a tmexCD1-toprJ1-positive plasmid with a broad host range, which evidenced that the widespread prevalence of tmexCD1-toprJ1 is possible due to such kinds of plasmids in the future. In addition, we found diversity and heterogeneity of translocatable units containing tmexCD1-toprJ1 in the plasmids. We also investigated the genetic features of tmexCD1-toprJ1 in online databases, which led to the proposal of the umuC gene as the potential insertion site of tmexCD1-toprJ1. Collectively, this study enriches the epidemiological and genomic characterization of tmexCD1-toprJ1 and provides a theoretical basis for preventing an increase in tmexCD1toprJ1 prevalence. IMPORTANCE Tigecycline, the first member of the glycylcycline class of antibacterial agents, is frequently used to treat complicated infections caused by multidrug-resistant Gram-positive and Gram-negative bacteria. The emergence of a novel plasmidmediated efflux pump, TmexCD1-ToprJ1, conferring resistance to multiple antimicrobials, including tigecycline, poses a huge risk to human health. In this study, we investigated the prevalence of tmexCD1-toprJ1-positive strains along the food production chain and found that tmexCD1-toprJ1 was mainly distributed in IncFIB(Mar)/ HI1B hybrid plasmids of K. pneumoniae. We also observed a potential risk of transmission of such plasmids along the pork processing chain, which finally may incur a threat to humans. Furthermore, the IncFIB(Mar)/HI1B tmexCD1-toprJ1-positive plasmids with a limited host range and specific insertion sites of tmexCD1-toprJ1 are strong evidence to prevent a fulminant epidemic of tmexCD1-toprJ1 among diverse pathogens. The mobilization and dissemination of tmexCD1-toprJ1, especially when driven by plasmids, deserve sustained attention and investigations.