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The emergence of novel plasmid-mediated high-level tigecycline resistance genes tet(X) in the Enterobacteriaceae has increased public health risk for treating severe bacterial infections. Despite growing reports of tet(X)-positive isolates detected in animal sources, the epidemiological association of animal- and environment-derived isolates with human-derived isolates remains unclear. Here, we performed a comprehensive analysis of tet(X4)-positive Escherichia coli isolates collected in a hospital in Guangdong province, China. A total of 48 tet(X4)-positive E. coli isolates were obtained from 1001 fecal samples. The tet(X4)-positive E. coli isolates were genetically diverse but certain strains that belonged to ST48, ST10, and ST877 etc. also have clonally transmitted. Most of the tet(X4) genes from these patient isolates were located on conjugative plasmids that were successfully transferred (64.6%) and generally coexisted with other antibiotic resistance genes including aadA, floR, bla TEM and qnrS. More importantly, we found the IncX1 type plasmid was a common vector for tet(X4) and was prevalent in these patient-derived strains (31.3%). This plasmid type has been detected in animal-derived strains from different species in different regions demonstrating its strong transmission ability and wide host range. Furthermore, phylogenetic analysis revealed that certain strains of patient and animal origin were closely related indicating that the tet(X4)-positive E. coli isolates were likely to have cross-sectorial clonal transmission between humans, animals, and farm environments. Our research greatly expands the limited epidemiological knowledge of tet(X4)-positive strains in clinical settings and provides definitive evidence for the epidemiological link between human-derived tet(X4)-positive isolates and animal-derived isolates., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)

Tigecycline serves as one of the antibiotics of last resort to treat multidrug-resistant (including carbapenem-resistant) pathogens. However, the recently emerged plasmid-mediated tigecycline resistance mechanism, Tet(X), challenges the clinical efficacy of this class of antibiotics. In this study, we detected 180 tet (X)-harboring Acinetobacter isolates (8.9%, n  = 180) from 2,018 samples collected from avian farms and adjacent environments in China. Eighteen tet (X)-harboring isolates (10.0%) were found to cocarry the carbapenemase gene bla NDM-1 , mostly from waterfowl samples (94.4%, 17/18). Interestingly, among six Acinetobacter strains, tet (X) and bla NDM-1 were found to colocalize on the same plasmids. Moreover, whole-genome sequencing (WGS) revealed a novel orthologue of tet (X) in the six isolates coharboring tet (X) and bla NDM-1 Inverse PCR suggested that the two tet (X) genes form a single transposable unit and may be cotransferred. Sequence comparison between six tet (X)- and bla NDM-1 -coharboring plasmids showed that they shared a highly homologous plasmid backbone even though they were isolated from different Acinetobacter species (three from Acinetobacter indicus , two from Acinetobacter schindleri , and one from Acinetobacter lwoffii ) from various sources and from different geological regions, suggesting the horizontal genetic transfer of a common tet (X)- and bla NDM-1 -coharboring plasmid among Acinetobacter species in China. Emergence and spread of such plasmids and strains are of great clinical concern, and measures must be implemented to avoid their dissemination., (Copyright © 2020 American Society for Microbiology.)