bla NDM-1 Carried by a Transferable Plasmid in a Salmonella Strain Isolated from Healthy Individuals.

OBJECTIVE

Our study aimed to conduct genomic characterization of Salmonella strains carrying the bla NDM-1 gene in the intestinal tract of healthy individuals. The objectives were to underscore the importance of genomic surveillance for drug resistance in both commensal and pathogenic bacteria among healthy populations, and to establish protocols for regulating drug resistance plasmids based on the completion of a comprehensive map of drug resistance plasmid genomes.

METHODS

We performed antimicrobial susceptibility testing and employed second- and third-generation sequencing techniques to analyze Salmonella strains harboring the bla NDM-1 gene, to surveil drug-resistant bacteria in the intestines of healthy subjects. Sequence comparison was conducted using both core- and pan-genome approaches. Concurrently, conjugation experiments were carried out to assess the efficiency of plasmid transfer.

RESULTS

We isolated a carbapenem-resistant Salmonella enterica serovar Typhimurium strain from a healthy food worker in China. This strain harbored an IncHI2/IncHI2A plasmid carrying bla NDM-1 along with multiple antibiotic resistance genes (ARGs). Our findings highlight the potential for asymptomatic carriers to facilitate the transmission of ARGs. Pan-genomic analysis revealed that bla NDM-1-positive plasmids could traverse bacterial species barriers, facilitating cross-host transmission.

CONCLUSION

This study marks the first detection of bla NDM-1 in Salmonella strains isolated from healthy individuals. We underscore the risk associated with the transmission of conjugative hybrid plasmids carrying bla NDM-1, which have the potential to be harbored and transmitted among healthy individuals. Enhanced surveillance of drug-resistant pathogens and plasmids in the intestinal microbiota of healthy individuals could provide insights into the risk of ARG transmission and pathways for population-wide dissemination via ARG transfer factors.