Antimicrobial Effects of Four Lactobacilli Strains Isolated from Yoghurt against E scherichia Coli O157:H7

Abstract

This study aimed to isolate Lactobacillus species from yoghurt and to evaluate its antimicrobial activity against enterohemorrhagic Escherichia coli O157:H7. After incubation of different yoghurt samples in MRS (de Man, Rogosa and Sharpe) agar at 37C under anaerobic conditions, four Lactobacillus species, L. casei, L. acidophilus, L. helveticus and L. delbrueckii ssp. bulgaricus were identified. Standard growth curves of E. coli O157:H7 in proximity with lactobacilli test strains were obtained. The antibacterial effects of lactobacilli cell debris and culture supernatant against E. coli O157:H7 were determined. The results showed that the antibacterial effects of culture supernatant were stable at different temperature conditions (56–100C) for 30 and 60 min; also, it was stable at pH 3–10. With regard to the antibacterial effect of the lactobacilli strains in this study, they may help in the treatment of E. coli O157:H7-associated diseases and can be applied as a biological preservative in the food industry. Practical Applications In recent years, foodborne diseases become a health problem in most of the population. One of the most important etiologic agents of such diseases is Escherichia coli O157:H7, which can be transmitted through eating undercooked infected meat and leads to hemorrhagic diarrhea and kidney failure. There is increasing evidence that lactobacilli bacteria produce potential agents (H2O2, small organic compounds, lactic acid, etc.) that can inhibit growths of some invasive foodborne bacteria, such as enterohemorrhagic E. coli. The results of this study also confirmed these reports and showed that the use of lactobacilli bacteria is a promising way to prevent the infection of E. coli O157:H7; also, they can be used as a biological preservative in the food industry.