Anti-listerial and Anti-biofilm Activities of Potential Probiotic Lactobacillus Strains Isolated from Tunisian Traditional Fermented Food

Three Lactobacilli were isolated from traditional Tunisian fermented food and then characterized for its ability to inhibit Listeria monocytogenes growth. Antagonistic effect of Lactobacillus plantarum on four L.monocytogenes strains was tested in soft artisanal cheese. Anti-biofilm activity of Lactobacillus extracts was also tested. Our results demonstrate that the selected lactic acid bacteria (LAB) extract exhibited a good antibacterial effect against L.monocytogenes ATCC 19115 with low MICs values: 8.33 +/- 2.1, 20 +/- 1.2 and 23.33 +/- 1, respectively. L.plantarum also exhibited a stronger inhibitory effect against L.monocytogenes when grown in cheese. Moreover, a potential anti-biofilm effect of the three LAB extracts with BIC50 values ranging from 5% to 15% for L.monocytogenes ATCC 19115 was demonstrated. Although LAB extracts were able to eradicate significantly a preformed L.monocytogenes biofilm (P<0.05). Growth inhibition of preformed biofilm was more difficult to achieve. LAB could be used as a bioprotective culture in cheese ripening to prevent Listeria growth. Practical Applications A wide range of lactic acid bacteria (LAB) produce bacteriocins, which were essentially active against the food-borne pathogen Listeria monocytogenes. 2, 3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) reduction method was used to assess the anti-biofilm and anti-listerial activity of LAB extract. XTT reduction assay is dependent on the microbial respiratory activity. Since XTT is used for quantification of the microbial respiratory activity, it was used to quantify viable mature biofilm and to compare LAB activity against planktonic and biofilm cells.