Bacteriocins of four lactobacilli species isolated from yogurt can inhibit growth and verotoxins production in E. coli O157: H7

Abstract

Lactic Acid bacteria are associated with rich habitats in nutrients, such as various food products and plant materials; they can produce compounds such as organic acids, hydrogen peroxide, diacetyl and bacteriocin or bactericidal proteins. The aim of present study was to evaluate the inhibitory effect of yogurt lactobacilli bacteriocins on the growth and verotoxins production of E.coli O157: H7. four Lactobacilli species (Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus bulgaricus and Lactobacillus helveticus) were isolated from local yogurts and their bacteriocins investigated by agar-well-diffusion,SDS page, Minimum Inhibitory Dilution (MID), Vero cell cytotoxicity and VTEC-RPLA assays. All the species had antibacterial activity against E.coli O157: H7and were effective on the inhibition of verotoxins production. Verotoxin production inhibited by L.casei and L. acidophilus in 1.32 and 1.64 dilutions, L.bulgaricus in 1.16, 1.32 and 1.64 and L. helveticus in 1.8, 1.16 and 1.32. Culture supernatant of L.acidophilus, L.casei and L.bulgaricus were resistant to heating at 56آ°C, 80آ°C and 100آ°C for 10, 30 and 60 min, but the bacteriocin produced by L.helveticus was inactivated in 100آ°C for 60 minutes. The former culture supernatants were stable between pH 3 and 10 but the latter bacteriocin (L.helveticus) was detected to be sensitive to pH 10. All the lactobacilli culture supernatants maintained full stability after storage for 30 days at -20آ°C and partial stability in 60 days at 4آ°C and no activity in 60 to 120 days at 37آ°C. All four lactobacilli produced a bacteriocin-like protein (10.4 KDa). Findings of this study shows that these bacteriocin-like substances might be useful as a starter culture and natural preservative. The inhibition of the bacterial growth or production of enterotoxins such as verotoxins by administrating lactobacilli bacteriocins would be of great importance.