Antagonistic effect of lactobacilli isolated from camel (Camelus dromedarius) milk on food borne pathogens

Camel milk is a suitable substrate for the growth of protective bacterial flora. Detection of lactic acid bacteria producing antimicrobial substances from camel (Camelus dromedarius) milk in south Algeria against some food-borne pathogens is the subject of this work. Morphological, physiological and biochemical tests have identified four Lactobacillus isolates belonging to the following species: Lactobacillus fermentum, Lactobacillus helviticus, Lactobacillus plantarum and Lactobacillus acidophilus. In order to demonstrate the inhibitory effect of these bacteria in vitro, their antagonistic property was tested against six pathogenic strains often involved in food-borne illness: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis and Shigella flexneri using the disc diffusion method. The antagonistic effect was manifested by the appearance of inhibition zones around the discs. The potential inhibitor was estimated by calculating diameter of inhibition zones which extend from 02 to 16 mm. All Lactobacillus isolates secreted into the culture medium inhibitory substances were able to inactivate the growth of pathogenic strains tested. L. plantarum has shown the largest inhibition zone against S. aureus (16 mm). These two strains were chosen to determine the nature of L. plantarum secreted substances responsible for the antagonistic effect. The obtained results have shown that L. plantarum inhibitory property against S. aureus resulted from the combined effect of several biological agents originating from their metabolic activities, especially organic acids and bacteriocins.