Abstract
INTRODUCTION: Salmonella 4,[5],12:i:-, a globally emerging pathogen with multidrug resistance (MDR), is spreading in China. Nationwide data on the antimicrobial resistance (AMR) and genomic characteristics of Salmonella 4,[5],12:i:- from human sources in China are scarce. This study aimed to characterize the prevalence, genetic diversity, and AMR profiles of Salmonella 4,[5],12:i:- in China. METHODS: All information, including geographical data, antimicrobial susceptibility test results, and whole-genome sequences, was extracted from the Chinese Pathogen Identification Network database from 2017 to 2023. Antimicrobial resistance phenotypes of 2,736 human-derived isolates were determined, and genomic analysis was applied to assess their genetic heterogeneity. Additionally, resistance genes were detected. RESULTS: Salmonella 4,[5],12:i:- strains exhibited varying levels of resistance to the tested antibiotics, with an overall resistance rate of 98.83%, MDR rate of 87.98%, and cefotaxime resistance of 25.91%. An increasing trend was observed for resistance to key antibiotics and AMR determinants from 2020-2023. Whole-genome analysis revealed five clades with high genetic diversity (A-E), with 97.33% belonging to ST34. Clade D carried a significant proportion of ESBL genes. Moreover, we identified 15 meropenem-resistant isolates primarily harboring widely distributed plasmids containing multiple resistance genes, including bla (NDM-5) and bla (OXA-10). CONCLUSION: Salmonella 4,[5],12:i:- is highly sporadic in China but remains phylogenetically linked to the prevalent MDR clone with a distinct resistance profile worldwide. The emergence of elevated resistance to third-generation cephalosporins and sharp rise in carbapenem resistance, coupled with the detection of plasmid-mediated resistance determinants, suggests the evolution of endemic MDR clones circulating within China. These findings emphasize the need for enhanced surveillance, stricter regulations on antibiotic use in agriculture, comprehensive risk factor surveys, and targeted interventions to prevent outbreaks.