Transmission of a plasmid harboring NDM-1 gene between Salmonella Typhimurium and Escherichia coli strains in an infant.

BACKGROUND

NDM-1 has been frequently identified in Enterobacteriaceae strains from clinical samples, but its occurrence in Salmonella Typhimurium (S. Typhimurium) is uncommon. Moreover, reports on the transmission of a plasmid harboring NDM-1 between different species in clinical samples are rare.

METHODS

Two S. Typhimurium strains and an Escherichia coli (E. coli) strain were isolated from a 14-month-old infant presenting with diarrhea. The resistance phenotypes were determined using the VITEK 2 Compact System. Genomic DNA was extracted from the isolated strains and whole genome sequencing was performed. The transmissibility of plasmids was validated by a conjugation experiment.

RESULTS

The subsequently isolated S. Typhimurium and E. coli strains exhibited resistance to imipenem, and whole genomic analysis revealed that each strain harbored a plasmid harboring NDM-1 and Qnrs1 genes. The two plasmids were nearly identical based on their sequences and could transfer to recipient strains. A genomic region containing several genes encoding phosphoribosylanthranilate isomerase, bleomycin binding protein, subclass B1 metallo-beta-lactamase, and IS30-like element ISAba125 family transposase was surrounded by the two flanking IS26 elements.

CONCLUSION

The transfer of plasmid harboring NDM-1 between S. Typhimurium and E. coli strains within patients highlights the potential for widespread transmission between different species. Continuous monitoring these strains may be important for preventing extensive transmission of resistance genes.