Antibacterial Effect of Non-industrial Yogurt on Salmonella and Shigella

Yogurt is one of the most consumed foods with different probiotic effects. The aim of this study was to evaluate antimicrobial effects of non-industrial yogurts on two common enteropathogens – Salmonella and Shigella. In this experimental study, we evaluated the antimicrobial effects of 30 various non-industrial yogurt samples on 11 Shigella sonnei, 7 Shigella flexneri, 2 Shigella boydii, and 15 Salmonella enteritidis isolates. All bacterial isolates were locally isolated from patients suffering from diarrhea. Using the well diffusion method, we evaluated the antimicrobial effect of whey protein from yogurt before and after 24 hours incubation at 42°C. The data was analyzed using independent t test and chi-square in SPSS (version 11.5). P value less than 0.05 was considered significant. None of the yogurts had antimicrobial effect on Shigella and Salmonella isolates before 24 hours incubation at 42°C. After incubation, however, 9 (30%) and 12 (40%) samples out of the 30 yogurt samples showed antimicrobial effects on 25%-50% and less than 25% of isolates, respectively. Six yogurt samples (20%) did not have any antimicrobial effects. Only 1 yogurt sample exhibited antimicrobial effect on more than 50% of the tested isolates. Our results suggested that some samples of non-industrial yogurts have an antibacterial effect on Shigella and Salmonella. However, neither of them had an influence on more than 51.5% of isolates. Therefore, reliance on yogurt as a standalone treatment is not recommended.