Carbapenem resistance mediated by bla NDM-13 in a highly drug-resistant Salmonella Stanley ST29 strain in China

The rise of carbapenem-resistant Enterobacterales presents a substantial global public health challenge. While carbapenem-resistant Salmonella is rarely reported in clinical settings, this study characterizes a carbapenem resistance mediated by bla NDM-13 Salmonella Stanley strain SAL22057, isolated from the fecal sample of a pediatric patient with diarrhea and fever. We determined antimicrobial susceptibility, conducted genomic characterization, and assessed plasmid conjugation. Antimicrobial susceptibility testing showed that SAL22057 was resistant to meropenem (minimum inhibitory concentration [MIC] 32 μg/mL) and imipenem (MIC 16 μg/mL). Genotyping analysis identified SAL22057 as belonging to ST29, and it was found to be multidrug-resistant and to carry numerous virulence genes. Whole-genome sequencing and plasmid analysis identified that bla NDM-13 was located on pSAL22057-NDM (IncI1 α ), while a distinct plasmid, pSAL22057-OXA (IncHI2), harbored multiple antimicrobial resistance genes, including bla OXA-10 . Conjugation experiments revealed that bla NDM-13 was transferable to Escherichia coli C600. We show that IS 1294 likely mediates bla NDM-13 mobilization, with its insertion influencing gene transfer. Furthermore, the consistent flanking of several resistance genes by IS 26 elements indicates that IS 26 -mediated horizontal gene transfer is a key mechanism driving the dissemination of these determinants and genomic rearrangements within Enterobacteriaceae . IMPORTANCE The emergence of carbapenem-resistant Enterobacterales poses a global health threat. This study identified a carbapenem-resistant Salmonella Stanley strain, SAL22057, from a pediatric patient, which carried the carbapenemase gene bla NDM-13 . The genotyping revealed that SAL22057 is ST29, displaying a concerning multidrug-resistant phenotype along with several virulence determinants. Alarmingly, this strain exhibits high-level resistance to meropenem (minimum inhibitory concentration [MIC] 32 μg/mL) and imipenem (MIC 16 μg/mL). Conjugation experiments confirm that bla NDM-13 is transferable to Escherichia coli C600, signaling a clear pathway for resistance dissemination among Enterobacteriaceae . We demonstrate that IS 1294 likely mobilizes bla NDM-13 , while IS 26 consistently flanks multiple resistance genes, providing mechanistic evidence that IS 26 -mediated transposition is accelerating the spread of resistance genes in clinical pathogens.