Molecular epidemiological and genetic variability of Salmonella isolates from the tropical mountainous region of southern China (2017-2024).

UNLABELLED: Salmonella enterica is a leading foodborne pathogen worldwide, posing significant public health concerns. However, its prevalence in mountainous regions in China remains unclear. This study analyzed 384 Salmonella strains isolated from 2,540 samples collected between 2017 and 2024 from humans, food, and environmental sources in tropical mountainous areas of China. Whole-genome sequencing and antimicrobial-susceptibility testing were performed to investigate genomic characteristics and antimicrobial resistance profiles. The results showed that S. I 1,4 [5],12:i:- (ST34, 43.5%) was the predominant serovar among diarrheal patients, while S. Enteritidis (ST11, 40%) was the primary causative serovar associated with systemic infections characterized by bacteremia. In food and environmental samples, S. Typhimurium (ST19, 39.1%) and S. Enteritidis (ST11, 35.1%) were most frequently isolated, respectively. Antimicrobial susceptibility testing revealed high resistance rates to ampicillin (63.8%), tetracycline (62.7%), ciprofloxacin (17.7%), cefotaxime (16.4%), and ceftazidime (15.6%), with 115 isolates (29.9%) identified as multidrug-resistant. Notably, six isolates were tigecycline-resistant, including two harboring tet(X4) genes on an IncFIA(HI1)-IncHI1A- IncHI1B(R27) hybrid plasmid. The distribution of virulence genes varied across strains from different sources and serovars. Genes encoding carbonic anhydrase (mig-5), plasmid-encoded fimbriae (pefA, pefB, pefC, and pefD), and type III secretion system effectors (spvB, spvC, and spvD) were significantly more prevalent in strains from patients with systemic infection than in those from diarrhea cases. The cdtB gene encoding typhoid toxin was identified in 19 non-typhoidal strains. This study presents the first comprehensive report on the prevalence and genetic dynamics of S. enterica in tropical mountainous regions of southern China, offering insights into novel interventions.

IMPORTANCE

Salmonella is a serious zoonotic foodborne pathogen and the third leading cause of death from human diarrheal diseases worldwide. In this study, we report, for the first time, a systematic surveillance of Salmonella prevalence among clinical patients, food, and environmental sources in the tropical mountainous regions of southern China from 2017 to 2024. Our findings illuminate the prevalence and genetic dynamics of S. enterica across diverse sources, as well as differences between patients with diarrheal disease and those with systemic infections characterized by bacteremia. Moreover, we observed high resistance to clinically important treatment drugs, including fluoroquinolones and third-generation cephalosporins, in these regions. These results provide critical evidence to inform more effective surveillance, treatment, and control strategies in tropical settings and underscore the need for continuous, real-time monitoring of pathogen dynamics.