Antimicrobial activity of neutralized extracellular culture filtrates of lactic acid bacteria isolated from a cultured Indian milk product ('dahi').

Neutralized extracellular culture filtrate obtained from isolates of Lactobacillus acidophilus, Lactobacillus delbruecki ssp. bulgaricus, Lactobacillus salivarius and Lactococcus lactis ssp. lactis from 'dahi' showed weak to moderate inhibition of Staphylococcus aureus, Bacillus cereus, Escherichia coli, Bacillus brevis, Bacillus circulans, Bacillus coagulans, Bacillus laterosporus, Bacillus subtilis and Pseudomonas aeruginosa when tested by the diffusion agar well assay method. The effective minimum quantity of lactic culture filtrates required to obtain complete inhibition of an inoculum of 10(3) cfu/ml of the bacteria tested was between 20 and 26% (vol/vol), as determined by the agar incorporation method. Neutralized extracellular culture filtrate of these lactic cultures added at a level of 10% in sterile, 10% reconstituted non-fat dry milk was able to either suppress or retard growth of selected bacterial cultures when incubated at 37 degrees C for 24 h. This study indicated the antimicrobial activity of dahi and the potential of using neutralized extracellular culture filtrate of lactic acid bacteria in the biopreservation of foods.