Bacteriocin Activity of Lactic Acid Bacteria Isolated from Nunu, a Spontaneously Fermented Milk

Abstract

According to literature, lactic acid bacteria have been used for ages as a natural preservative for dairy products as well as protective cultures.This is mainly due to their production of antimicrobial substances like organic acids and bacteriocins and their ability to compete against pathogenic and spoilage bacteria for nutrients. Nunu is a fermented dairy product enjoyed by the people of West Africa. This work was carried out for the purpose of identifying the antagonistic effects of bacteriocins of four lactic acid bacteria namely Lb. fermentum, Lb, plantarum, Lb. mesenteroides and W. confusa against some pathogenic/spoilage organisms which include Strep. faecalis, Sal. typhimirum, E. coli ATTC 24522, B. cereus and P. aeruginosa. Each of the LAB has different strains isolated at different times during the fermentation process.The activity shown by the bacteriocin against Gram negative bacteria is an unusual phenomenon and defies the observations of Klaenhammer, (1988) that bacteriocins are proteins which show inhibitory activity against closely related organisms. However, in this study, the bacteriocins of LAB strains were effective against Gram negative bacteria including E. coli ATCC 24522, P.  aeruginosa and Sal. typhimirum. This was even to the extent that the highest antagonistic effect, 15.5 mm, was exhibited by P. aeruginosa against Lb. mesenteroides 6-7, though some the bacteriocins showed some antagonistic effects against the Gram positive bacteria with the highest being 14.5 mm shown by Lb. mesenteroides 0-23 against Strep. faecalis. B. cereus being another Gram positive bacterium was inhibited by only the bacteriocins of W. confusa 24-17.The present findings was supported by the observations made earlier by Mandal et al., (2008). According to the present study, starter cultures for nunu production can be made from Lb. mesenteroides 6-7 and W. confusa 24-17 and the fermentation allowed to take place within 48 hours.