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

Background: The plasmid−mediated tigecycline resistance gene tet(X4) confers a high level of resistance to tigecycline. The experiment aims to investigate the prevalence and characterization of tet(X4) in Escherichia coli isolates from chicken and pig farms in Hunan province, China. Methods: A total of six tet(X4) positive strains were identified in 257 E. coli derived from chicken samples in Xiangtan city (n = 2), pig samples in Xiangxiang city (n = 1), Chenzhou city (n = 2), and Zhuzhou city (n = 1). The presence of tet(X4) was directly detected by PCR assay, and then the broth dilution method determined the antimicrobial susceptibility profile of the tet(X4)−positive isolates. Genomic locations were identified by whole−genome sequencing (WGS) and bioinformatics. Results: Almost all tet(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 tet(X4)−bearing strains exhibited six distract STs, such as ST10, 202, ST218, ST362, ST2077, ST7068. The plasmid replicon types carrying tet(X4) were the hybrid plasmid IncFIA(HI1)/IncHIA/IncHIB(R27) (5/6) and IncX1 (1/6). Conclusions: The presence of similar genetic environments in E. coli 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.