Genomic characterization of antimicrobial resistance, virulence, and transmission of non-typhoidal Salmonella from retail red meat in Hunan, China.

INTRODUCTION

Salmonella is a major foodborne pathogen frequently transmitted via retail meat. This study comprehensively characterized the genomic features of non-typhoidal Salmonella from retail red meat in Hunan, China, including antimicrobial resistance, virulence determinants, and transmission patterns.

METHODS

We characterized 147 Salmonella isolates from retail red meat (pork, beef, and mutton) collected in Hunan, China (2021 and 2023) using whole-genome sequencing and antimicrobial susceptibility testing to investigate their resistance and genomic characteristics.

RESULTS

High resistance rates were observed: 115 isolates (78.2%) were resistant to at least one agent, and 92 (62.6%) were multidrug-resistant (MDR). The predominant serotypes were Salmonella London (25.2%) and S. Typhimurium (24.5%). Critically, the 16S rRNA methyltransferase gene rmtB was identified in three isolates (2.0%)-the only amikacin-resistant isolates. The extended-spectrum β-lactamase (ESBL) gene bla CTX-M-55 was detected in six isolates (4.1%), and plasmid-mediated AmpC genes (bla CMY-2/bla DHA-1) in three (2.0%). Of major concern, the complete typhoid toxin gene cluster (cdtB, pltA, pltB) was identified in 14 non-typhoidal Salmonella (NTS) isolates (9.5%) across diverse serotypes. Core-genome multilocus sequence typing (cgMLST) revealed 22 genomic clusters, demonstrating multi-level transmission from regional sources to local outbreaks.

DISCUSSION: These findings highlight the emergence of multidrug-resistant Salmonella clones carrying clinically significant resistance and virulence determinants in retail red meat, underscoring the need for enhanced food chain surveillance.