Occurrence and Molecular Characterization of Abundant tet (X) Variants Among Diverse Bacterial Species of Chicken Origin in Jiangsu, China

Many novel tigecycline-inactivating enzymes encoded by (X) variants from different bacteria were discovered since the plasmid-mediated (X3) and (X4) genes conferring high-level resistance to tigecycline in Enterobacterales and were reported. However, there have been no comprehensive studies of the prevalence of different (X) variants in poultry farms. In this study, we collected 45 chicken fecal samples, isolated (X)-positive strains, and performed antimicrobial susceptibility testing, conjugation assay, whole-genome sequencing, and bioinformatics analysis. A total of 15 (X)-bearing strains were isolated from 13 samples. Species identification and (X) subtyping analysis found that the 15 strains belonged to eight different species and harbored four different (X) variants. Genomic investigation showed that transmission of (X) variants was associated with various mobile genetic elements, and (X4) was the most prevalent variant transferred by conjugative plasmids. Meanwhile, we characterized a plasmid co-harboring (X6) and in . In summary, we demonstrated that different (X) variants were widely disseminated in the chicken farming environment and dominated by (X4). This finding expands the understanding of the prevalence of (X) among different animal sources, and it was advocated to reduce the usage of antibiotics to limit the emergence and transmission of novel (X) variants in the poultry industry.