Emerging <i>bla</i> _NDM -positive <i>Salmonella enterica</i> in Chinese pediatric infections

Non-typhoidal <i>Salmonella</i> (NTS) is a common zoonotic foodborne pathogen, whose rising antimicrobial resistance has been an urgent threat to global public health. Here, we reported two carbapenem-resistant <i>Salmonella enterica</i> (CRSE) strains (NBFE-049 and NBFE-164) carrying the <i>bla</i> _NDM genes, which were recovered from two Chinese children, belonged to <i>Salmonella enterica</i> serovar Typhimurium (<i>S</i>. Typhimurium) monophasic variant (<i>S</i>. 1,4,[5],12:i:-) ST34 (a sequence type) and <i>S</i>. Typhimurium ST19, respectively. Genes <i>bla</i> _NDM-5 and <i>bla</i> _NDM-13 were detected in NBFE-049 and NBFE-164, respectively. The <i>bla</i> _NDM-5 in NBFE-049 was located in an IncHI2-type plasmid, named pNBFE-049. In NBFE-164, the <i>bla</i> _NDM-13 was located in an IncI1-type plasmid, named pNBFE-164. The plasmid pNBFE-164 successfully transferred its resistance phenotype into the recipient strain <i>Escherichia coli</i> J53 with a high efficiency of 1.1 × 10^-2, while no transconjugants were obtained in pNBFE-049 conjugation assays. We further elucidated the genetic relationships of globally occurring New Delhi Metallo-β-lactamase (NDM)-positive strains and locally distributed clinical strains within the same serovar. The closest relative of NBFE-049 was clinical <i>Salmonella</i> strain 1722, which was recovered in 2020 and differed by only three Single Nucleotide Polymorphisms (SNPs). No NDM-positive ST19 could be found in the National Center for Biotechnology Information (NCBI) database, and NBFE-164 showed a close genetic relationship with the other ST19 in this area. To sum up, we suggested the potential contributions of clonal spread and plasmid-mediated <i>bla</i> _NDM transfer in CRSE dissemination. This study reported the complete genome of two <i>bla</i> _NDM-carrying <i>S</i>. Typhimurium isolates, shedding new insights into the antimicrobial resistance mechanisms and dissemination patterns of the emerging CRSE.IMPORTANCENTS is one of the most common zoonotic pathogens that causes foodborne illnesses, while <i>S</i>. Typhimurium is one of the most common serovars. With the rising prevalence of multi-resistant <i>Salmonella</i> worldwide, carbapenems have emerged as the last-line antibiotics for treating severe bacterial infections. In this study, we reported the genomic characteristics of two carbapenem-resistant <i>S</i>. Typhimurium strains, which were recovered from two pediatric patients, carrying <i>bla</i> _NDM-5 and <i>bla</i> _NDM-13, providing new insights into the antimicrobial resistance deteriminants and transmission risk of <i>bla</i> _NDM-positive NTS in China. We suggested the potential contributions of clonal spread and plasmid-mediated <i>bla</i> _NDM transfer in CRSE dissemination. Future enhanced surveillance policy should mitigate CRSE spreading, and more importantly, clinical antimicrobial therapeutic regimens should be adjusted accordingly.