Characteristics of tet (X4)-Producing Escherichia coli in Chicken and Pig Farms in Hunan Province, China

The plasmid-mediated tigecycline resistance gene (X4) confers a high level of resistance to tigecycline. The experiment aims to investigate the prevalence and characterization of (X4) in isolates from chicken and pig farms in Hunan province, China. A total of six (X4) positive strains were identified in 257 derived from chicken samples in Xiangtan city ( = 2), pig samples in Xiangxiang city ( = 1), Chenzhou city ( = 2), and Zhuzhou city ( = 1). The presence of (X4) was directly detected by PCR assay, and then the broth dilution method determined the antimicrobial susceptibility profile of the (X4)-positive isolates. Genomic locations were identified by whole-genome sequencing (WGS) and bioinformatics. Almost all (X4)-positive strains showed high resistance to multidrug, including tigecycline. Resistome analysis revealed many antibiotic resistance genes, including those with resistance to tetracyclines, β-lactams, phenicols, quinolones, lincosamides chloramphenicol, aminoglycosides and sulfamids. These (X4)-bearing strains exhibited six distract STs, such as ST10, 202, ST218, ST362, ST2077, ST7068. The plasmid replicon types carrying (X4) were the hybrid plasmid IncFIA(HI1)/IncHIA/IncHIB(R27) (5/6) and IncX1 (1/6). The presence of similar genetic environments in from different cities suggests there may be horizontal transmission pathways promoting the broad spread of drug-resistant genes in Hunan Province, putting great pressure on multidrug resistance monitoring.