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ABSTRACT


In the present study interaction between three lactic acid bacteria species and three food borne pathogenic bacteria species were studied. The objective of the study was to determine the effect of those interactions to the antimicrobial compound producing ability of lactic acid bacteria. Using the three lactic acid bacteria namely, Lactococcus lactis, Lactobacillus acidophilus and Lactobacillus casei and three pathogenic bacteria namely, Salmonella enterica, Escherichia coli and Listeria monocytogenes 56 different culture combinations were prepared and grown in a medium invented by de Man, Rogosa and Sharpe MRS broth. Then Cell Free Filtrates CFF containing antimicrobial compounds were obtained from all those cultures and tested for antimicrobial activity against the three pathogenic microorganisms. All Cell Free Filtrates CFF were found to be having antibiotic activity against tested three pathogenic bacteria. Antibiotic activity of Cell Free Filtrates CFF obtained from cultures contained both lactic acid bacteria and some pathogenic bacteria were significantly higher than cultures contained only lactic acid bacteria. However, this stimulating effect of pathogenic bacteria on antimicrobial compound production by lactic acid bacteria was different for different pathogenic bacteria. Stimulation by Escherichia coli was not observed and some times Escherichia coli shown to be reducing the antimicrobial compound production. Antibiotic activity was found to be higher in mixed cultures of lactic acid bacteria compared to individual cultures. Results of this study confirm the importance of using mixed cultures and effective stimulant bacteria in antimicrobial compound production by lactic acid bacteria.

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