Genetic Diversity and Antibiotic Resistance Profiling of Salmonella Isolates from Diarrhea Patients in Chifeng, China.

Salmonella is known to cause intestinal infections in humans, which can result in symptoms such as diarrhea, vomiting, and, in severe cases, sepsis and death. Isolates of Salmonella from specific populations and regions exhibit varying patterns of antibiotic resistance and genetic characteristics. This study aims to evaluate the diversity of 32 strains of Salmonella isolated from fecal samples of diarrhea patients in Chifeng City, China, between 2021 and 2023, through antibiotic resistance and genomic analysis. Microbroth dilution and whole genome sequencing were employed to investigate antibiotic resistance, multilocus sequence typing, phylogenetic relationship, virulence genes, antibiotic resistance genes, and mobile genetic elements. The antibiotic resistance tests showed 93.75% of Salmonella isolates were resistant to ampicillin, followed by streptomycin (STR) (87.50%) and tetracycline (TET) (56.25%). A total of 32 Salmonella strains were classified into 6 ST types. Virulence gene profiles revealed a relatively high prevalence of the type III secretion system gene cluster. The adhesion-related genes fim, Bcf, and Agf/Csg were prominently represented across all isolates. The antibiotic resistance gene profile showed that the aminoglycoside resistance gene aac(6')-Iaa (100.00%), sulfanilamide resistance gene sul (81.25%), β-lactam resistance gene blaTEM-1B (75.00%), and TET resistance gene tet (56.25%) were more commonly found. Plasmid replicons IncFII(S), IncFIB(S), IncQ1, and IncX1 were frequently identified in these isolates, serving as primary sources of horizontally acquired foreign genes. The most common phage types were Salmon_118970_sal3 (78.13%) and Phage_Gifsy_2 (59.38%). The most frequently observed insertion sequences were IS285 (56.25%) and ISEc39 (56.25%) from the IS256 family. The results indicate a correlation between the resistance phenotype of Salmonella and its genomic characteristics. These findings provide valuable references for the prevention and control of Salmonella, as well as for clinical treatment.