Characterization of Three Porcine Strains Co-Harboring (X3) and .

Tigecycline is the antibiotic of last resort for the treatment of extensively drug-resistant bacterial infections, mainly those of multidrug-resistant Gram-negative bacteria. The plasmid-mediated (X3) gene has recently been described in various pathogens that are resistant to tigecycline. We report three tigecycline-resistant strains isolated from porcine faeces in China, which all contained the (X3)-harboring plasmids. A broth microdilution method was used to examine the antimicrobial susceptibility of the isolates, and S1-Nuclease digestion pulsed-field gel electrophoresis (S1-PFGE) was used to characterize their plasmid profiles. The whole-genome sequences of the isolates were determined with the Nanopore PromethION platform. The sequence analysis indicated that the strains were They showed resistance to multiple antibiotics, and all the resistance genes were located on plasmids. The three (X3)-harboring plasmids had a similar backbone structure, and all contained with various insertion elements (IS). IS is considered an important factor in (X3) mobilization. In addition to IS, we demonstrate that IS generates a circular intermediate containing the (X3) gene, which could increase the dissemination risk. To our knowledge, this is the first report of (X3)- and -harboring plasmids in . Because the IS is frequently found in front of (X3), research should be directed toward the action of IS in the spread of (X3).