Bile salts and cholesterol induce changes in the lipid cell membrane of Lactobacillus reuteri

TARANTO, MARIA PIA; FERNANDEZ MURGA, LEONOR; LORCA, GRACIELA; FONT DE VALDEZ, GRACIELA

JOURNAL OF APPLIED MICROBIOLOGY

Blackwell

Año: 2003 vol. 95 p. 86 - 89

1364-5072

AIMS: The objective of this study was to evaluate the effect of bile salts and/or cholesterol in the lipid profile of Lactobacillus reuteri CRL 1098, as well as to determine whether a relationship exists between these changes and 1) the in vitro removal of cholesterol by Lact. reuteri CRL 1098 (reported previously), and 2) the tolerance of the cells to acid and cold stress. METHODS AND RESULTS: Lact. reuteri CRL 1098 was grown  into the following media: MRS (MC, control medium), MB (MC with bile salts), MCH (MC with the addition of 1% sterile cholesterol), and MBCH (with bile salts and cholesterol). Total fatty acids were extracted, methyl esterified and determined by analytical gas-liquid chromatography. The polar lipids were characterized by their migrations on thin-layer chromatographic (TLC) plates and the total amount of phospho- and glycolipids was determined by colorimetric techniques. Finally, the cell suspensions of different culture media were subjected to cold and acid stress. The cultures grown with bile salts displayed a decrease in phospholipids and a relative increase in glycolipids as well as a low ratio of saturated: unsaturated fatty acids, and differences in the relative ratios of the fatty acid species. The presence of the unusual hydroxy C18:0,10-OH and oxo C18:0,10-oxo fatty acids was the prominent characteristic of the bile salts-growing cells. Comparison of cyclic (C19-cyc) and unsaturated fatty acids (C18:1, C18:2) revealed that they are inversely related. The relative increase in glycolipids, and the changes in the fatty acids profiles of bile-growing cells would be responsible for the ability of this strain to remove cholesterol. The modifications in the lipid profile induced by bile salts and in a less extent by cholesterol produced a decrease in the tolerance of Lact. 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 lactic acid bacteria 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 Lact. reuteri, an enterolactobacillus of probiotic value. The steady-state response of the cells subjected to bile stress seems to be the appropriate model for bacterial growth in detergent-containing gastrointestinal tracts, where the bile salts stress would presumably be continuous.