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

Abstract

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 <i>tmexCD1-toprJ1</i>, 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 <i>tmexCD1-toprJ1</i>-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 <i>tmexCD1-toprJ1</i>-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 <i>tmexCD1-toprJ1</i> and dominated the horizontal dissemination of <i>tmexCD1-toprJ1</i> among K. pneumoniae isolates. However, in this study, we identified the IncR plasmid as a <i>tmexCD1-toprJ1</i>-positive plasmid with a broad host range, which evidenced that the widespread prevalence of <i>tmexCD1-toprJ1</i> is possible due to such kinds of plasmids in the future. In addition, we found diversity and heterogeneity of translocatable units containing <i>tmexCD1-toprJ1</i> in the plasmids. We also investigated the genetic features of <i>tmexCD1-toprJ1</i> in online databases, which led to the proposal of the <i>umuC</i> gene as the potential insertion site of <i>tmexCD1-toprJ1</i>. Collectively, this study enriches the epidemiological and genomic characterization of <i>tmexCD1-toprJ1</i> and provides a theoretical basis for preventing an increase in <i>tmexCD1-toprJ1</i> prevalence. <b>IMPORTANCE</b> 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 plasmid-mediated 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 <i>tmexCD1-toprJ1</i>-positive strains along the food production chain and found that <i>tmexCD1-toprJ1</i> 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 <i>tmexCD1-toprJ1</i>-positive plasmids with a limited host range and specific insertion sites of <i>tmexCD1-toprJ1</i> are strong evidence to prevent a fulminant epidemic of <i>tmexCD1-toprJ1</i> among diverse pathogens. The mobilization and dissemination of <i>tmexCD1-toprJ1</i>, especially when driven by plasmids, deserve sustained attention and investigations.