Epidemiological features and antibiotic resistance of Salmonella strains isolated from diarrheal cases in Gansu Province, China, 2024.

内容摘要

Salmonella is a significant global health threat, particularly in developing areas. This study elucidated the epidemiological features, serotypes, antibiotic resistance patterns, and molecular evolutionary relationships of 91 Salmonella strains isolated from diarrhea cases in Gansu Province, China, in 2024. Antibiotic susceptibility was assessed using the broth microdilution method. Whole-genome sequencing and bioinformatics analyses were performed to determine serotype, genetic relationships, antimicrobial resistance gene prevalence, and virulence gene profiles. Among the 91 strains, the majority (56.04%, 51/91) were isolated from children aged 0-9 years, indicating this group as a high-risk population. Of the strains, 41.76% (38/91) originated from Lanzhou City and 17.59% (16/91) from Qingyang. In total, 20 distinct serotypes were identified, with monophasic Salmonella Typhimurium serovar 1,4,[5],12:i:- being the most prevalent at 34.07% (31/91), followed by serovar Enteritidis at 25.27% (23/91). Genetic diversity revealed 22 sequence types corresponding to these serotypes. The antibiotic resistance profiles indicated high resistance rates (>50%) to several antibiotics: streptomycin (69.0%), ampicillin (78.0%), cefazolin (58.0%), tetracycline (55.0%), and ampicillin/sulbactam (55.0%). Notably, 80.22% (73/91) of the strains exhibited multidrug resistance. Substantial serotype-specific differences in resistance gene profiles were observed: serotype 1,4,[5],12:i:- carried high frequencies of heavy metal resistance genes (e.g., silver, 83.9%), while serotype London uniquely harbored quaternary ammonium disinfectant resistance genes (71.4%). Quinolone resistance genes had the highest detection rate (81.32%), followed by streptomycin (70.33%) and sulfonamide (68.13%) resistance genes. Formal testing of genotype-phenotype association revealed a weak and non-significant correlation (Spearman ρ = 0.14, p > 0.05), indicating that resistance gene carriage alone does not fully predict phenotypic resistance. Phylogenetic analysis based on core genome multilocus sequence typing identified 15 minimum spanning tree clusters, with the largest cluster comprising ST11 Salmonella enterica. Additionally, isolates from Lanzhou and Baiyin City shared identical single nucleotide polymorphism characteristics, suggesting a potential risk of inter-regional transmission. Virulence gene analysis confirmed that all strains possessed intact SPI-1/SPI-2 pathogenicity islands (carriage rates 92.7-98.5%) and lacked Vi capsule genes, consistent with their non-typhoidal status and diarrheal presentation. This study reveals an alarming multidrug resistance rate, predominance of specific serotypes, and potential inter-regional transmission of epidemic clones in Gansu Province, underscoring the urgent need for enhanced genomic surveillance and targeted interventions.