The inhibitory effect of bacteriocins produced by yogurt Lactobacilli on the growth and verotoxins production of enterohemorrhagic Escherichia coli O157:H7 (EHEC) was investigated. Three Lactobacilli species (Lactobacillus acidophilus, Lactobacillus bulgaricus and Lactobacillus helveticus) were isolated from commercial yogurts. The antibacterial activity against E. coli O157: H7was examined and the results showed that all the species were effective. They were also effective on the inhibition of verotoxins production. The inhibition against verotoxins was observed at the concentrations lower than the Minimum Inhibitory Dilution (MID) of each lactobacilli bacteriocin, indicating that these lactobacilli bacteriocins would preferentially prevent the production of verotoxins rather than have bactericidal effect on EHEC. We also found that bacteriocins of L. acidophilus and L. bulgaricus were resistant to heating at 56, 80 and 100°C for 10, 30 and 60 min, but the bacteriocin produced by L. helveticus was inactivated by heating at 100°C for 30 and 60 min. Also the former bacteriocins were stable between pH 3 and 10 but the latter bacteriocin (L. helveticus) was considered to be sensitive to pH 10. It was observed that all the bacteriocins produced by the test isolates maintained full stability after storage for 30 days at -20°C and partial stability after storage for 60 days at 4°C while no activity was detected after storage for 60 to 120 days at 37°C.
M. Zarringhalam Moghaddam, M. Sattari , A.M. Mobarez and F. Doctorzadeh , 2006. Inhibitory Effect of Yogurt Lactobacilli Bacteriocins on Growth and Verotoxins Production of Enterohemorrhgic Escherichia coli O157:H7. Pakistan Journal of Biological Sciences, 9: 2112-2116.