Emergence of a Plasmid-Encoded Resistance-Nodulation-Division Efflux Pump Conferring Resistance to Multiple Drugs, Including Tigecycline, in Klebsiella pneumoniae

Abstract

Transporters belonging to the chromosomally encoded resistance-nodulation-division (RND) superfamily mediate multidrug resistance in Gram-negative bacteria. However, the cotransfer of large gene clusters encoding RND-type pumps from the chromosome to a plasmid appears infrequent, and no plasmid-mediated RND efflux pump gene cluster has yet been found to confer resistance to tigecycline. Here, we identified a novel RND efflux pump gene cluster, designated <i>tmexCD1-toprJ1</i>, on plasmids from five pandrug-resistant <i>Klebsiella pneumoniae</i> isolates of animal origin. TMexCD1-TOprJ1 increased (by 4- to 32-fold) the MICs of tetracyclines (including tigecycline and eravacycline), quinolones, cephalosporins, and aminoglycosides for <i>K.</i><i>pneumoniae</i>, <i>Escherichia coli</i>, and <i>Salmonella</i> TMexCD1-TOprJ1 is closely related (64.5% to 77.8% amino acid identity) to the MexCD-OprJ efflux pump encoded on the chromosome of <i>Pseudomonas aeruginosa</i> In an IncFIA plasmid, pHNAH8I, the <i>tmexCD1-toprJ1</i> gene cluster lies adjacent to two genes encoding site-specific integrases, which may have been responsible for its acquisition. Expression of TMexCD1-TOprJ1 in <i>E. coli</i> resulted in increased tigecycline efflux and in <i>K. pneumoniae</i> negated the efficacy of tigecycline in an <i>in vivo</i> infection model. Expression of TMexCD1-TOprJ1 reduced the growth of <i>E. coli</i> and <i>Salmonella</i> but not <i>K. pneumoniae</i><i>tmexCD1-toprJ1</i>-positive <i>Enterobacteriaceae</i> isolates were rare in humans (0.08%) but more common in chicken fecal (14.3%) and retail meat (3.4%) samples. Plasmid-borne <i>tmexCD1-toprJ1</i>-like gene clusters were identified in sequences in GenBank from <i>Enterobacteriaceae</i> and <i>Pseudomonas</i> strains from multiple continents. The possibility of further global dissemination of the <i>tmexCD1</i>-<i>toprJ1</i> gene cluster and its analogues in <i>Enterobacteriaceae</i> via plasmids may be an important consideration for public health planning.<b>IMPORTANCE</b> In an era of increasing concerns about antimicrobial resistance, tigecycline is likely to have a critically important role in the treatment of carbapenem-resistant <i>Enterobacteriaceae</i>, the most problematic pathogens in human clinical settings-especially carbapenem-resistant <i>K.</i><i>pneumoniae</i> Here, we identified a new plasmid-borne RND-type tigecycline resistance determinant, TMexCD1-TOprJ1, which is widespread among <i>K. pneumoniae</i> isolates from food animals. <i>tmexCD1-toprJ1</i> appears to have originated from the chromosome of a <i>Pseudomonas</i> species and may have been transferred onto plasmids by adjacent site-specific integrases. Although <i>tmexCD1-toprJ1</i> still appears to be rare in human clinical isolates, considering the transferability of the <i>tmexCD1-toprJ1</i> gene cluster and the broad substrate spectrum of TMexCD1-TOprJ1, further dissemination of this mobile tigecycline resistance determinant is possible. Therefore, from a "One Health" perspective, measures are urgently needed to monitor and control its further spread. The current low prevalence in human clinical isolates provides a precious time window to design and implement measures to tackle this.