Emergence of tigecycline-resistant Escherichia coli from swine feces and fertilized soil.

The emergence and spread of tigecycline-resistant Escherichia coli in livestock environments poses a critical threat to global public health. This study investigated the prevalence, genetic characteristics, and transmission mechanisms of tet(X4)-mediated tigecycline resistance in E. coli from swine feces and swine feces-fertilized soil in China. All 200 E. coli strains were resistant to at least one antibiotic, among which 95.50 % (191/200) were multi-drug resistant (MDR). A total of 13 tigecycline-resistant E. coli strains (5.18 %) were identified, all exhibiting MDR. Second-generation sequencing analysis highlighted strong positive associations between resistance genes (e.g., aminoglycosides and macrolides) and virulence factors (e.g., hlyF, tsh, iucC, and iutA), suggesting a synergistic survival advantage. However, tet(X4) was negatively correlated with virulence factors (hlyF, iucC, and iutA), revealing that the presence of tet(X4) may reduce the expression of virulence genes. ST10 was the dominant sequence type, and many plasmid types were identified in tet(X4)-positive E. coli strains. The IncX1-type plasmid pLKYW52 carrying tet(X4) harbored type IV secretion system (T4SS)-related genes (virB4, virB9, ptlE, and ptlH), which may facilitate plasmid conjugation and bacterial adaptation. Expression of tet(X4) in Bacillus megaterium significantly reduced antibiotic efficacy, showing Tet(X) ability for tetracycline degradation. These findings highlight the role of agricultural practices in propagating antibiotic resistance and emphasize the urgent need for targeted interventions to mitigate the spread of high-risk MDR pathogens.