In an era of increasing concerns about antimicrobial resistance, tigecycline is likely to have a critically important role in the treatment of carbapenem-resistant Enterobacteriaceae , the most problematic pathogens in human clinical settings—especially carbapenem-resistant K. pneumoniae . Here, we identified a new plasmid-borne RND-type tigecycline resistance determinant, TMexCD1-TOprJ1, which is widespread among K. pneumoniae isolates from food animals. tmexCD1-toprJ1 appears to have originated from the chromosome of a Pseudomonas species and may have been transferred onto plasmids by adjacent site-specific integrases. Although tmexCD1-toprJ1 still appears to be rare in human clinical isolates, considering the transferability of the tmexCD1-toprJ1 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.

Three kinds of plasmid-mediated quinolone resistance (PMQR) determinants have been discovered and have been shown to be widely distributed among clinical isolates: qnr genes, aac(6 ′ )-Ib-cr , and qepA . Few data on the prevalence of these determinants in strains from animals are available. The presence of PMQR genes in isolates from animals was determined by PCR amplification and DNA sequencing. The production of extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases in the strains was detected, and their genotypes were determined. The genetic environment of PMQR determinants in selected plasmids was analyzed. All samples of ceftiofur-resistant (MICs ≥ 8 μg/ml) isolates of the family Enterobacteriaceae were selected from 36 companion animals and 65 food-producing animals in Guangdong Province, China, between November 2003 and April 2007, including 89 Escherichia coli isolates, 9 Klebsiella pneumoniae isolates, and isolates of three other genera. A total of 68.3% (69/101) of the isolates produced ESBLs and/or AmpC β-lactamases, mainly those of the CTX-M and CMY types. Of the 101 strains, PMQR determinants were present in 35 (34.7%) isolates, with qnr, aac(6 ′ )-Ib - cr , and qepA detected alone or in combination in 8 (7.9%), 19 (18.8%), and 16 (15.8%) strains, respectively. The qnr genes detected included one qnrB4 gene, four qnrB6 genes, and three qnrS1 genes. Five strains were positive for both aac(6 ′ )-Ib - cr and qepA , while one strain was positive for qnrS1, aac(6 ′ )-Ib - cr , and qepA. qnrB6 was flanked by two copies of IS CR1 with an intervening dfr gene downstream and sul1 and qacE Δ 1 genes upstream. In another plasmid, aac(6 ′ )-Ib-cr followed intI1 and arr-3 was downstream. PMQR determinants are highly prevalent in ceftiofur-resistant Enterobacteriaceae strains isolated from animals in China. This is the first report of the occurrence of PMQR determinants among isolates from companion animals.

The presence and characterization of plasmid-mediated fosfomycin resistance determinants among Escherichia coli isolates collected from pets in China between 2006 and 2010 were investigated. Twenty-nine isolates (9.0%) were positive for fosA3 , and all of them were CTX-M producers. The fosA3 genes were flanked by IS 26 and were localized on F2:A−:B− plasmids or on very similar F33:A−:B− plasmids carrying both bla _CTX-M-65 and rmtB . These findings indicate that the fosA3 gene may be coselected by antimicrobials other than fosfomycin.