[Contamination and Molecular Epidemiological Characteristics of Salmonella in Fruits, Vegetables, and Irrigation Water]

Objective: To explore the genomic epidemiological characteristics of Salmonella in fruits, vegetables, and irrigation water in China.

Methods: A total of 410 samples of fruits, vegetables and irrigation water were collected from Hubei and Shaanxi Provinces from June to December 2022. Salmonella strains were detected and identified referenced in the United States Food and drug administration's bacteriological analytical manual. The antimicrobial susceptibility to 17 antibiotics in 9 classes was assessed by broth microdilution, and the serotype and antibiotic resistance genes(ARG) were predicted by whole genome sequencing technology.

Results: In total, 29 strains of Salmonella were collected. There were 3 strains isolated from fruits and vegetables, 25 from irrigation water, and 1 from soil fertilizers. The detection rate in irrigation water(22.32%) was higher than that in fruits, vegetables(1.46%), and soil fertilizers(1.08%). The individual detection rate(13.01%) was higher than the large-scale monitoring point detection rate(4.03%). Based on the analysis of the whole genome sequencing, a total of 19 serotypes were identified, with S. Thompson being the most frequently detected serotype(24.14%).31.0% of isolates showed resistance to the tested drugs and showed the highest resistance to cotrimoxazole, tetracycline, ampicillin.24.1% were multi-drug resistant strains and were resistant to 14 kinds of antimicrobial compounds belonging to 8 categories. Moreover, based on the whole-genome sequence analysis of antibiotic resistance genes, it was found that the carriage rate of aminoglycoside ARGs was 100%, and the carriage rates of other ARGs were folate pathway antagonists, fosfomycins, tetracyclines, phenicols, sulfonamids, quinolones, beta-lactam, macrolids and rifamycins were 31.03%, 27.59%, 27.59%, 27.59%, 24.14%, 20.69%, 6.90%, and 6.90%, respectively. Over 30% of the strains carried more than 6 antibiotic resistance genes.

Conclusion: Salmonellas were detected in fruits, vegetables, irrigation water and soil fertilizer in Hubei and Shaanxi Provinces. The strains isolated from irrigation water exhibiting a diverse range of serotypes and carrying numerous antibiotic resistance genes. More intensive efforts should be made on the monitoring of Salmonella and its antibiotic resistance in irrigation water.