Plasmid-borne tigecycline resistance gene tet(X4) in Salmonella enterica and Escherichia coli isolates from one diarrhea pediatric patient infections, China

Antibiotic resistance poses a growing threat to public health, necessitating vigilant surveillance and probing transmission mechanisms. In this study, we identified tigecycline-resistant Escherichia coli and Salmonella enterica isolates co-harboring the transferable tigecycline resistance gene tet(X4) in a pediatric patient The emergence of tet(X4)-positive S. enterica is a noteworthy finding, shedding light on the evolving landscape of antibiotic resistance. Both isolates were highly resistant to tigecycline and susceptible to carbapenems. The tet(X4) gene was located on >180 kb IncFIA/IncHI1A/IncHI1B plasmids with 99.94% homology between the two isolates. This plasmid can be efficiently transferred between Enterobacteriaceae by conjugation. Further comparative genomics revealed its likely hybrid evolution from similar plasmids previously found in bacteria of vegetable, meat and human gut origin. In addition, phylogenetic evidence suggests clonal spread of genetically closely related S. enterica in 12 out of 14 countries. The coexistence of multidrug resistance and intrinsic virulence genes is a cause for concern. This study reinforces the risk of a transferable mechanism underlying the global spread of tigecycline resistance. Urgent surveillance and control efforts targeting tet(X4) among different bacteria species are warranted.