Research – Microbiological Profile, Prevalence and Characterization of Salmonella enterica in Peanuts, Pecans, Raisins, Sun-dried Tomatoes, and Chocolate Sprinkles Sold in Bulk in Markets of Queretaro, Mexico 

Journal of Food Protection

In Mexico, the prevalence of Salmonella enterica in low water activity foods and their link to outbreaks is unknown. The aim of this study was to determine the microbiological profile and the prevalence of S. enterica in low water activity foods (peanuts, pecans, raisins, sun-dried tomatoes, and chocolate sprinkles) purchased in retail establishments in Queretaro, Mexico. Seventy samples of each food item sold in bulk were purchased. Aerobic plate count (APC), molds, yeasts, total coliforms, Escherichia coli, and Staphylococcus aureus were quantified in 10-g samples. The prevalence of S. enterica in 25 g samples was determined. From positive samples, S. enterica  isolates (60) were characterized based on their antimicrobial susceptibility to 14 antibiotics, the presence/absence of 13 virulence genes and serotype. The concentration of APC, molds, yeast, total coliforms, and E. coli ranged from 3.1-5.2 Log CFU g-1, 2.0-2.4 Log CFU g-1, 2.0-3.0 Log CFU g-1, 0.6-1.1 Log MPN g -1, and 0.5-0.9 Log MPN g -1, respectively. S. aureus  was not detected in any sample (<10 CFU g -1). The prevalence of  S. enterica in chocolate sprinkles, raisins, peanuts, pecans, and sun-dried tomatoes was 26%, 29%, 31%, 40%, and 52%, respectively. Most isolates (68.3%) were resistant to at least one antibiotic. The chromosome-associated virulence genes were found in all isolates and only one strain had sopE, and 98.3% of the isolates were grouped in the same virulotype. Among the isolates, the most frequent serotype was Tennessee (51/60). According to the characteristics evaluated, the isolates were grouped in 24 clusters. The elevated prevalence of S. enterica highlight the role of low water activity food items sold in bulk at markets as a potential vehicle for pathogens transmission. Regardless of the low variability among S. enterica isolates, their characterization could be helpful to elucidate which strains are circulating in these foods for improving epidemiological surveillance.

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