Cloning and expression of colicin E2 genes in Lactococcus lactis LM0230 and its inhibition against Escherichia coli O157:H7 in fermented milk.

摘要

Twenty-one colicin producing strains were used to evaluate the inhibitory activity of colicins against 6 Gram-negative microorganisms, Escherichia coli O157:H7, Salmonella typhimurium, Shigella boydii, Yersinia enterocolica, Aeromonas hydrophila, and Pseudomonas putida . The overlay technique was used to assess inhibition of the Gram-negative strains on Luria agar. Group A colicins were more effective inhibitiors than colicins in Group B. Colicins E2, E4, E7, G and H were effective against all tested pathogens but not against Pseudomonas. Among all the colicins colicin E2 was the most effective against E. coli O157:H7, while no colicins tested inhibited Pseudomonas putida. Among these 21 colicins, colicin 1a and 1b did not inhibit any of the tested strains. This study clearly indicated some colicins, like colicin E2, M and colicin E7 may be used as biopreservatives to aid in control of some Gram-negative bacteria in food.; Colicin E2 was selected as the subject for subsequent studies against E. coli O157:H7. Successful cloning and expression of ColE2 in Lactococcus suggests some bacteriocins produced by Gram-negative bacteria can be expressed successfully by Gram positive bacteria in the absence of lysis protein or signal peptide.; Application of Colicin E2 producing Lactococcus strains as inhibitors of E. coli O157:H7 was studied further in a fermented milk system. There was not an obvious difference in reducing E. coli O157:H7 in milk and fermented milk when 8 and 12 RU colicin E2 used. This study indicated the direct addition of colicin E2 to food can inhibit E. coli O157:H7 growth.; Results of this study indicate colicins may be an important option to control Gram-negative food borne spoilage and pathogens. Colicin E2 encoding genes can be incorporated into a lactococcus plasmid, expressed, and secreted into the environment as in E. coli strains. Adding colicin E2 directly into fermented milk may be a practical method to control E. coli O157:H7 if regulatory issues can be overcome. (Abstract shortened by UMI.)