Journal of Pure and Applied MicrobiologyVol. 8 No. 6

Bacteriocins of Four Lactobacilli Species Isolated from Yogurt can Inhibit Growth and Verotoxins Production in E. coli O157: H7

Maryam Zarringhalam Moghaddam1, Mohammad Reza Nahaei2, Hossein Samadi Kafil3 and Firozeh Safaeyan3*

1Department of Microbiology, International Branch of Shahid Beheshti Medical University, Tehran, Iran. 2Tabriz Infectious Disease and Tropical Medicine Research Center, Tabriz University of Medical Sciences, Tabriz, Iran. 3Drug Applied Research Center, Tabriz University of Medical Sciences,Tabriz, Iran.

Received on 25 July 2014 and accepted on 02 September 2014

 

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 56?C, 80?C and 100?C for 10, 30 and 60 min, but the bacteriocin produced by L.helveticus was inactivated in 100?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 ?20?C and partial stability in 60 days at 4?C and no activity in 60 to 120 days at 37?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.

Keywords : Enterohemorrhagic Escherichia coli O157:H7, Lactobacillus, Yogurt, minimum inhibitory dilution (MID).