Genomic Insights into the First Emergence of blaNDM-5-Carrying Carbapenem-Resistant Salmonella enterica Serovar London Strain in China

Carbapenem-resistant Salmonella enterica (S. enterica) pose a significant threat to public health, causing gastroenteritis and invasive infections. We report the first emergence of a carbapenem-resistant S. enterica serovar London strain, A132, carrying the bla NDM-5 gene in China. Whole-genome sequencing and bioinformatics analysis assigned A132 to be ST155, a multidrug-resistant clone frequently reported in China. The strain A132 exhibited resistance to multiple antibiotics, with 20 acquired antibiotic resistance genes (ARGs) identified, predominantly located on the IncFIB plasmid (pA132-1-NDM). Notably, the bla NDM-5 gene was located within an IS 26 flanked-class 1 integron-IS CR1 complex, comprising two genetic cassettes. One cassette is the class 1 integron, which may facilitate the transmission of the entire complex, while the other is the bla NDM-5 -containing IS CR1- IS 26- flanked cassette, carrying multiple other ARGs. Genbank database search based on the bla NDM-5 -carrying cassette identified a similar genetic context found in transmissible IncFIA plasmids from Escherichia coli (p91) and Enterobacter hormaechei (p388) with a shared host range, suggesting the potential for cross-species transmission of bla NDM-5 . To our knowledge, this is the first reported case of Salmonella serovar London ST155 harboring bla NDM-5 gene. Phylogenetic analysis indicated a close relationship between A132 and eight S . London ST155 strains isolated from the same province. However, A132 differed by carrying the bla NDM-5 gene and four unique ARGs. Given the high transmissibility of the F-type plasmid harboring bla NDM-5 and 18 other ARGs, it is imperative to implement vigilant surveillance and adopt appropriate infection control measures to mitigate the threat to public health.