IS15DIV-flanked composite transposon harboring blaNDM-5 in multidrug-resistant Salmonella Typhimurium

Multidrug-resistant <i>Salmonella</i> Typhimurium has emerged as a global public health concern. Asymptomatic gastrointestinal carriage is a key factor in the spread of antibiotic-resistant bacteria. However, it is challenging to obtain direct evidence of <i>in vivo</i> transfer of mobile genetic elements (MGEs). Here, we found that MGEs harboring <i>bla</i> _NDM-5 were transferred from asymptomatic <i>Escherichia coli</i> (LS20223694) to <i>Salmonella</i> Typhimurium (LS20223695) in a child. BLAST analyses demonstrated that the IS<i>15DIV</i>-flanked composite transposon of pLS20223695_NDM5 showed high similarity with pLS20223694_NDM5 and two previously reported plasmids, suggesting the possibility of genetic recombination. Besides, conjugation experiments showed that the transconjugant carried the incompatibility group I1 (IncI1)-I(alpha) plasmid replicon with the <i>bla</i> _NDM-5 and <i>sul1</i> genes, indicating that pLS20223695_NDM5 is a conjugative plasmid with transferability. Our study provides insights into the genetic basis of an IS<i>15DIV</i>-flanked composite transposon in <i>Salmonella</i> Typhimurium.