Antimicrobial Resistance and Genomic Epidemiology of tet(X4)-Bearing Bacteria of Pork Origin in Jiangsu, China

The emergence of tigecycline-resistant bacteria in agri-food chains poses a public health concern. Recently, plasmid-mediated tet(X4) was found to be resistant to tigecycline. However, genome differences between tet(X4)-positive Escherichia coli of human and pork origins are still under-investigated. In this study, 53 pork samples were collected from markets in Jiangsu, China, and 23 tet(X4)-positive isolates were identified and shown to confer resistance to multiple antibiotics, including tigecycline. tet(X4)-positive isolates were mainly distributed in E. coli (n = 22), followed by Klebsiella pneumoniae (n = 1). More than half of the tet(X4) genes were able to be successfully transferred into E. coli C600. We downloaded all tet(X4)-positive E. coli isolates from humans and pork found in China from the NCBI database. A total of 42 known STs were identified, of which ST10 was the dominant ST. The number of ARGs and plasmid replicons carried by E. coli of human origin were not significantly different from those carried by E. coli of pork origin. However, the numbers of insertion sequences and virulence genes carried by E. coli of human origin were significantly higher than those carried by E. coli of pork origin. In addition to E. coli, we analyzed all 23 tet(X4)-positive K. pneumoniae strains currently reported. We found that these tet(X4)-positive K. pneumoniae were mainly distributed in China and had no dominant STs. This study systematically investigated the tet(X4)-positive isolates, emphasizing the importance of the continuous surveillance of tet(X4) in pork.