The effects of acid adaptation on cell membrane fatty acid acyl chains in bifidobacteria and Lactobacillus casei

Lactobacillus and Bifidobacterium species comprise a significant proportion of the cultures utilized for probiotic preparations. Fermented foods such as yogurt are vehicles of probiotic distribution. Fermented foods have high acidity and extended shelf lives. Once consumed, probiotics are exposed to successive stress factors within the human gastrointestinal tract. Together, these traits work together to reduce probiotic viability. Cells with increased acid tolerance may have increased industrial relevance.; Studies to induce an acid tolerance response (ATR) in 5 bifidobacteria species and Lactobacillus casei ATCC334 were conducted in an attempt to increase viability during subsequent acid challenge. The results suggested that different acid tolerance induction parameters are necessary for individual species. The results also suggested that the commercial strains of bifidobacteria and L. casei were able to host an ATR resulting in increased viability after acid challenge. Recently obtained human isolates were unable to host an ATR. These strains quickly lost viability during acid challenge.; A component of acid tolerance is the cells ability to alter the cell membrane (CM) fatty acid acyl chain composition. Studies were conducted to assess the changes in CM fatty acids after ATR induction. The results showed increased concentrations of saturated fatty acids after ATR induction in the commercial isolate of B. longum strains. The recently obtained human isolate did not increase the saturated fatty acids to the same extent. This may, in part, account for the decreased viability in this strain during acid challenge. L. casei CM fatty acid composition altered in response to ATR by a decrease in oleic (C18:19) and cis-vaccenic (C18:111) acids and an increase in the cyclopropane dihydrosterculic (ΔC19:09) and lactobacillic (ΔC19:011) acids. Saturated and cyclopropane fatty acids are thought to increase CM rigidity and decrease permeability. These modifications may aid in acid tolerance.