Résumé:
Lactic acid bacteria are widely used in food industry due to their role in the fermentation and preservation of food production by several factors such inhibitors and is the goal of this work of seeking the antagonistic power of four lactic strains that are Streptococcus thermophilus, Lactococcus lactis and two strains of Pediococcus acidilactici after having revived and confirmed their purity and identity by morphological and biochemical tests against pathogenic and alteration bacteria.
The method Barefoot and al, 1983 used in this research has shown that these lactic acid bacteria exert an inhibitory effect on pathogenic bacteria with different zones of inhibition diameters from one bacterium to another.
Indeed, the lactic strains exert a strong inhibitory effect of the growth of Gram positive bacteria (Staphylococcus aureus ATCC 25923) with diameters between 16mm and 20mm and a moderate effect according to strains against the Gram-negative species (E. coli ATCC 25922 and Pseudomonas aeruginos ATCC 27853) with diameters of4mm and 6mm and 0, 7mm, 9mm respectively and Candida albicans ATCC 10231 with the diameter of 6mm only for Lactococcus lactis . Measuring the optical density of the harmful bacteria shows that after rapid growth, the number of bacteria decreases rapidly after adding the supernatant of the lactic acid bacterium which contains at least one bacteriocin. Our isolates were found thermostable to heat treatment for 30 minutes at 80 ° C and 100 ° C pendant15minute but they are heat sensitive to the treatment of 120 ° C for 10 minutes and optimum production of bacteriocins is at a temperature of 30 ° C and 37 ° C. These characteristics suggest that these substances are extracellular, heat stable and proteinaceous confirming that they are bacteriocins. These results suggest that the use of lactic acid bacteria as probiotics permetterait well protect humans against the bacteria causing gastrointestinal diseases
