Human intestinal colonization by <i>Escherichia coli</i> ST4014 co-harboring <i>tet</i> (X4) and <i>bla</i> _NDM-1 gene: a potential reservoir for antimicrobial resistance dissemination

The emergence of <i>Escherichia coli</i> strains co-harboring <i>tet</i>(X4) and <i>bla</i>_NDM-1 genes in healthy individuals represents a critical public health concern. These genes mediate resistance to tigecycline and carbapenems, two of the few remaining options for treating infections caused by multidrug-resistant gram-negative bacteria. The detection of clonally related ST4014 strains carrying conjugative plasmids encoding both resistance determinants highlights the potential for horizontal gene transfer and silent dissemination of dual-resistance plasmids in community settings. Such colonization among healthy individuals suggests that antimicrobial resistance may be spreading unnoticed beyond hospitals, driven by environmental or foodborne transmission routes. These findings emphasize the urgent need for integrated genomic surveillance and One Health-based interventions encompassing human, animal, and environmental reservoirs to prevent the expansion of high-risk resistance genes and safeguard the clinical efficacy of last-line antibiotics.