Genomic characterization of tigecycline-resistant tet(X4)-positive E. coli in slaughterhouses

The tet(X4) gene has been discovered in various sources and is considered a hazardous genetic material in environments; however, the distribution of tet(X4) in pig slaughterhouse and its genetic background are not well understood. This study was conducted to determine the prevalence of tet(X4) in slaughterhouses, and revealed that tet(X4) was prevalent in slaughterhouses and was dominated by E. coli. The isolates carrying tet(X4) were observed in the large intestine, small intestine and cecum, with the isolates distributed in the cecum carrying the most abundant drug resistance genes. The genome analysis revealed that the E. coli sequence types were diverse and tet(X4) was carried by plasmids, indicating that the widespread transmission of tet(X4) in the slaughterhouse was mainly mediated by plasmids. Furthermore, an IncX1 plasmid carrying more resistance genes than the classical IncX1 plasmids was identified. For the first time, we observed an E. coli carrying tet(X4) and blaNDM-5 in slaughterhouse. Correlation analysis revealed that tet(X4) was positively correlated with ISCR2, floR, sul3 and IncX1. tet(X4)-positive E. coli from slaughterhouse and human sources have a high genetic similarity, suggesting a possibility of cross transmission. These findings indicate that slaughterhouses are important sources of tet(X4) and hotspot of transmission, and large-scale surveillance is urgently required to investigate the need for interventions to prevent tet(X4) transmission.