Metabolism of Bile Salts by Alimentary Bacteria During Transit in the Human Small Intestine

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Abstract
High numbers of alimentary bifidobacteria and lactobacilli survive their passage through the intestine. A majority of strains of Bifidobacterium and Lactobacillus can deconjugate or dehydroxylate bile salts. Our aim was to study whether the ingestion of a fermented milk (FM) containing bifidobacteria and L. acidophilus could influence the metabolism of bile salts in the small bowel. The study was randomised and double blinded. Eight ileostomy subjects received on two consecutive days the same meal plus a 100 g cup of an FM which either contained 107 CFU/g Bifidobacterium sp. and 108 CFU/g L. acidophilus, or had been pasteurised (as control). Heal effluents were collected for 6 h after meals. Effluent weight and excretion of the different bile salts were measured. These did not differ significantly between the two periods except ileal excretions of free and secondary bile salts which were significantly increased during the FM period. Rapid and extensive deconjugation of bile salts was observed during in vitro experiments with both strains, but no dehydroxylation was detected. Excessive metabolism of bile salts in the human small bowel can be detrimental, and we suggest that the absence or limited extent of bile salt transformation capacity of bacteria added to food should be a pre-requisite for labelling a product as GRAS (generally recognised as safe).