Cocktails of probiotics pre-adapted to multiple stress factors are more robust under simulated gastrointestinal conditions than their parental counterparts and exhibit enhanced antagonistic capabilities against Escherichia coli and Staphylococcus aureus

BACKGROUND The success of the probiotics in delivery of health benefits depends on their ability to withstand the technological and gastrointestinal conditions; hence development of robust cultures is critical to the probiotic industry. Combinations of probiotic cultures have proven to be more effective than the use of single cultures for treatment and prevention of heterogeneous diseases. We investigated the effect of pre- adaptation of probiotics to multiple stresses on their stability under simulated gastrointestinal conditions and the effect of their singular as well as their synergistic antagonistic effect against selected enteric pathogens. METHODS Probiotic cultures were inoculated into MRS broth adjusted to pH 2 and incubated for 2 h at 37°C. Survivors of pH 2 were subcultured into 2% bile acid for 1 h at 37°C. Cells that showed growth after exposure to 2% bile acid for 1 h were finally inoculated in fresh MRS broth and incubated at 55°C for 2 h. The cells surviving were then used as stress adapted cultures. The adapted cultures were exposed to simulated gastrointestinal conditions and their non- adapted counterparts were used to compare the effects of stress adaptation. The combination cultures were tested for their antipathogenic effects on Escherichia coli and Staphylococcus aureus. RESULTS Acid and bile tolerances of most of the stress-adapted cells were higher than of the non-adapted cells. Viable counts of all the stress-adapted lactobacilli and Bifidobacterium longum LMG 13197 were higher after sequential exposure to simulated gastric and intestinal fluids. However, for B. longum Bb46 and B. bifidum LMG 13197, viability of non-adapted cells was higher than for adapted cells after exposure to these fluids. A cocktail containing L. plantarum + B. longum Bb46 + B. longum LMG 13197 best inhibited S. aureus while E. coli was best inhibited by a combination containing L. acidophilus La14 150B + B. longum Bb46 + B. bifidum LMG 11041. A cocktail containing the six non- adapted cultures was the least effective in inhibiting the pathogens. CONCLUSION Multi-stress pre-adaptation enhances viability of probiotics under simulated gastrointestinal conditions; and formulations containing a mixture of multi stress-adapted cells exhibits enhanced synergistic effects against foodborne pathogens.