2.9. Bacteriocin activity

The antimicrobial activity of the bacteriocins was tested by the agar diffusion test method [25], using E. coli ATCC 8739 as the target strain. This strain does not contain the stx1 or stx2 genes coding for Shiga toxins [26]. To titrate the antibacterial activity of purified bacteriocins, the serial dilution method on agar medium was used. Thus, purified bacteriocins were acidified to a pH between 4.5 and 5 and sterilized by filtration. Serial double dilutions of the samples were performed and was added to the wells of BHI soft agar containing the E. coli ATCC 8739 indicator strain. The Petri dishes were then incubated at 37 °C for 18 h. The antibacterial activity was then determined in Arbitrary Units per millilitre (AU/mL) according to the following formula: 2ⁿ x (1000 μl/ deposited volume), with n corresponding to the highest number of dilution at which growth inhibition of the sensitive strain is observed [27].