An in vitro study of the probiotic potential of a bile-salt-hydrolyzing Lactobacillus fermentum strain, and determination of its cholesterol-lowering properties

Abstract

This study evaluated the use of a bile-salt-hydrolyzing Lactobacillus fermentum strain as a probiotic with potential hypocholesterolemic properties. The effect of L. fermentum on representative microbial populations and overall metabolic activity of the human intestinal microbiota was investigated using a three-stage continuous culture system. Also, the use of galactooligosaccharides as a prebiotic to enhance growth and/or activity of the Lactobacillus strain was evaluated. Administration of L. fermentum resulted in a decrease in the overall bifidobacterial population (ca. 1 log unit). In the in vitro system, no significant changes were observed in the total bacterial, Lactobacillus, Bacteroides, and clostridial populations through L. fermentum supplementation. Acetate production decreased by 9 to 27%, while the propionate and butyrate concentrations increased considerably (50 to 90% and 52 to 157%, respectively). A general, although lesser, increase in the production of lactate was observed with the administration of the L. fermentum strain. Supplementation of the prebiotic to the culture medium did not cause statistically significant changes in either the numbers or the activity of the microbiota, although an increase in the butyrate production was seen (29 to 39%). Results from this in vitro study suggest that L. fermentum KC5b is a candidate probiotic which may affect cholesterol metabolism. The short-chain fatty acid concentrations, specifically the molar proportion of propionate and/or bile salt deconjugation, are probably the major mechanism involved in the purported cholesterol-lowering properties of this strain.

FIG. 1.

Growth and deconjugation of bile acids. Changes in pH (▵) and growth (OD_{650 nm}) (▪) of L. fermentum KC5b (A), S. bovis ATCC 43143 (B), and E. faecalis UK873 (C) in MRS broth supplemented with 1 mM TCA (□) and 1 mM GCA (▴) are shown. Each point represents the mean of three trials; error bars represent standard deviations.

FIG. 2.

Growth of L. fermentum KC5b in MRS-C broth containing 1% (wt/vol) of glucose (▪), GOS (□), FOS (⧫), or lactulose (▵). Each point represents the mean of three independent trials; error bars represent standard deviations.

FIG. 3.

Influence of oxgall concentration on growth rate (▪) and cholesterol reduction (▵) of L. fermentum KC5b. Levels of cholesterol removed from the culture broth are expressed as mean percentages of the initial concentration during the 24-h incubation. Error bars represent standard deviations (n = 2).

FIG. 4.

L. fermentum numbers in V1 (⧫), V2 (□), and V3 (▴) of the three-stage continuous culture system. The left arrow indicates the start of the prebiotic addition to V1 (day 22), and the right arrow indicates the end of the probiotic addition to V1 (day 43). Each point represents the mean of three independent trials; error bars represent standard deviations.