Bile Salt Deconjugation and Cholesterol Removal from Media by Lactobacillus casei

Abstract

Lactobacillus casei N19 and E5 and Lactobacillus acidophilus L1 and ATCC 43121 were compared for their ability to deconjugate bile salts and remove cholesterol from MRS broth during growth at pH 6.0 and during growth without pH control. Samples grown without pH control dropped to pH 4.2 to 4.5 during 20 h of incubation, depending on the culture. The plate counts indicated that populations in all cultures were near their maximum numbers after 16 h of growth. The amount of cholesterol removed from the broth was similar for both strains of L. acidophilus grown with and without pH control. However, the strains of L. casei differed significantly in the amount of cholesterol removed during growth with or without pH control. Both cultures of L. casei that were grown at pH 6.0 removed very little cholesterol from the broth, but cells grown without pH control removed up to 60 micrograms of cholesterol/ml. All cultures of both species deconjugated 60 to 90% of the bile salts. Lactobacillus acidophilus L1 was the only culture to demonstrate differences between the two pH treatments in the amount of bile salts deconjugated; however, there was no difference in the amounts of cholesterol removed. These results indicate that most of the cholesterol removal from broth by L. acidophilus was due to assimilation, perhaps by the incorporation of cholesterol into the cellular membrane. Lactobacillus casei most likely removes cholesterol from broth by means of the destabilization of cholesterol micelles and the coprecipitation of the cholesterol with the deconjugated bile salts at pH less than 6.0.