effect of physical and chemical changes on the antimicrobial activity of culture supernatant fluid of lactic acid bacteria

abstract         background and objective: lactic acid bacteria are gram-positive, catalase-negative, nonsporulating, either rod- or coccus-shaped bacteria that have beneficial effects on their hosts by producing antimicrobial substances such as lactic acid, hydrogen peroxide, bacteriocins and biosurfactants. bacteriocins are antimicrobial peptides that are produced by bacteria and can inhibit the growth of other bacteria.        methods: in this experimental study, bacteriocin production by lactobacilli as known probiotic strains was evaluated in different physicochemical conditions. antagonistic activity was evaluated using quantitative method of microscale optical density assay (moda). after neutralization of acid and treatment with various enzymes, temperature, ph and nacl conditions, the antimicrobial activity of culture supernatant fluid of lactobacillus acidophilus and l. plantarum was investigated against pathogenic proteus.        results: the culture supernatant fluid of lactobacilli was sensitive to proteolytic enzymes with relatively good stability to temperature. the antimicrobial activity was also present due to production of bacteriocin under different nacl conditions (1 to 4% nacl) and ph range of 5 to 8.         conclusion: it seems that the antimicrobial liquid of lactobacillus strains contains bacteriocin, which shows antimicrobial effects against pathogenic strains of proteus. to investigate further this effect, some complementary studies should be performed.