Fecal Carriage of Escherichia coli Harboring the tet (X4)-IncX1 Plasmid from a Tertiary Class-A Hospital in Beijing, China.

The emergence of the mobile tigecycline-resistance gene, tet (X4), poses a significant threat to public health. To investigate the prevalence and genetic characteristics of the tet (X4)-positive Escherichia coli in humans, 1101 human stool samples were collected from a tertiary class-A hospital in Beijing, China, in 2019. Eight E. coli isolates that were positive for tet (X4) were identified from clinical departments of oncology ( n = 3), hepatology ( n = 2), nephrology ( n = 1), urology ( n = 1), and general surgery ( n = 1). They exhibited resistance to multiple antibiotics, including tigecycline, but remained susceptible to meropenem and polymyxin B. A phylogenetic analysis revealed that the clonal spread of four tet (X4)-positive E. coli from different periods of time or departments existed in this hospital, and three isolates were phylogenetically close to the tet (X4)-positive E. coli from animals and the environment. All tet (X4)-positive E. coli isolates contained the IncX1-plasmid replicon. Three isolates successfully transferred their tigecycline resistance to the recipient strain, C600, demonstrating that the plasmid-mediated horizontal gene transfer constitutes another critical mechanism for transmitting tet (X4). Notably, all tet (X4)-bearing plasmids identified in this study had a high similarity to several plasmids recovered from animal-derived strains. Our findings revealed the importance of both the clonal spread and horizontal gene transfer in the spread of tet (X4) within human clinics and between different sources.