Effect of Nutrient Media and Bile Salts on Growth and Antimicrobial Activity of Lactobacillus acidophilus

Abstract

The Lactobacillus acidophilus strains produced variable quantities of antimicrobial substances in three different media: Elliker's, MRS (deMan, Rogosa, and Sharpe), and LBS (Lactobacillus selection) broths. The interaction between L. acidophilus strain and nutrient medium was statistically significant, indicating an influence of the nutrient medium on the level of antimicrobial activity produced. Also statistically significant different were levels of the antimicrobial activity of different strains and the pH of the medium at the end of the fermentation period. Bile salts were added to MRS broth to simulate concentrations in gastrointestinal tract of humans. Antimicrobial activity as well as growth decreased in the presence of high concentrations of bile salts. Sodium glycocholate was more inhibitory than sodium taurocholate at equimolar levels. Calcium hydroxide was added to MRS broth at hourly intervals for 8h to adjust the pH of the fermentation medium to pH of 6.5, which resulted in a doubling of cell numbers. However, there were no differences in the levels of antimicrobial activity at the end of 24h. Although there were no differences in pH of the fermentation medium at the end of 24 and 48h, the antimicrobial activity increased after 24h of fermentation.