Aims: The objective of this study was to evaluate the effect of bile salts and cholesterol in the lipid profile of Lactobacillus reuteri CRL 1098 and to determine the relationship existing between these changes: the in vitro removal of cholesterol and the tolerance of the cells to acid and cold stress. Methods and Results: Lactobacillus reuteri CRL 1098 was grown in the following media: MRS (deMan Rogosa Sharpe; M C , control medium), M B (M C with bile salts), M CH (M C with sterile cholesterol) and M BCH (M C with bile salts and cholesterol). Fatty acids were determined by analytical gas-liquid chromatography, and phospholipids and glycolipids by colorimetric techniques. The cells from different culture media were subjected to cold and acid stress. The M B cultures displayed a decrease in phospholipids and a low ratio of saturated : unsaturated fatty acids. The presence of the unusual C18 : 0,10-OH and C18 : 0,10-oxo fatty acids was the prominent characteristic of the bile salts growing cells. The relative increase in glycolipids and the changes in the fatty acids profiles of the M B cells would be responsible for the cholesterol remotion. The changes induced by bile salts in the lipid profile did not improve the tolerance of L. reuteri CRL 1098 to freezing and acid stress. Conclusions: The changes in lipid profiles reported in this study would play a key role in the response of Lactobacilli to environmental stress. Significance and Impact of the Study: This work provides useful information about the effect of bile salts on the cell membrane of L. reuteri, a probiotic enterolactobacillus. The steady-state response of the cells subjected to bile stress seems to be the appropriate model for evaluating the bacterial behaviour in detergent-containing gastrointestinal tracts, where the bile salts stress would presumably be continuous.

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The effect of temperature and growth phase on the autolysis of Lactobacillus acidophilus CRL 640 was studied. The maximal rate of autolytic activity (ca 48% cell lysis) was found at 45 degrees C. At this temperature, two peaks were detected: the first one at the early exponential phase of growth and the second lysis peak during the transition stage from the exponential to the stationary phase. The release of intracellular compounds absorbing at 260 and 280 nm was also detected at 45 degrees C. The microscopic observations revealed morphological changes and the presence of ghost cells. At 37 degrees C, the low autolytic activity obtained would be related to the normal cell cycle of growth.