Characterization of IncHI1B Plasmids Encoding Efflux Pump TmexCD2-ToprJ2 in Carbapenem-Resistant Klebsiella variicola, Klebsiella quasipneumoniae, and Klebsiella michiganensis Strains

Abstract

Tigecycline serves as one of the last-resort antibiotics to treat severe infections caused by carbapenem-resistant Enterobacterales. Recently, a novel plasmid-mediated resistance-nodulation-division (RND)-type efflux pump gene cluster, <i>TmexCD1-ToprJ1</i>, and its variants, <i>TmexCD2-ToprJ2</i> and <i>TmexCD3-ToprJ3</i>, encoding tetracyclines and tigecycline resistance, were revealed. In this study, we reported three <i>TmexCD2-ToprJ2</i>-harboring <i>Klebsiella</i> species strains, collected from two teaching tertiary hospitals in China, including one <i>K. quasipneumoniae</i>, one <i>K. variicola</i>, and one <i>K. michiganensis</i>. The three strains were characterized by antimicrobial susceptibility testing (AST), conjugation assay, WGS, and bioinformatics analysis. AST showed that <i>K. variicola</i> and <i>K. quasipneumoniae</i> strains were resistant to tigecycline with MIC values of 4μg/ml, whereas the <i>K. michiganensis</i> was susceptible to tigecycline with an MIC value of 1μg/ml. The <i>TmexCD2-ToprJ2</i> clusters were located on three similar IncHI1B plasmids, of which two co-harbored the metallo-β-lactamase gene <i>bla</i> _NDM-1. Conjugation experiments showed that all three plasmids were capable of self-transfer <i>via</i> conjugation. Our results showed, for the first time, that this novel plasmid-mediated tigecycline resistance mechanism <i>TmexCD2-ToprJ2</i> has spread into different <i>Klebsiella</i> species, and clinical susceptibility testing may fail to detect. The co-occurrence of <i>bla</i> _NDM-1 and <i>TmexCD2-ToprJ2</i> in the same plasmid is of particular public health concern as the convergence of "mosaic" plasmids can confer both tigecycline and carbapenem resistance. Its further spread into other clinical high-risk <i>Klebsiella</i> clones will likely exacerbate the antimicrobial resistance crisis. A close monitoring of the dissemination of <i>TmexCD-ToprJ</i> encoding resistance should be considered.