Relationship Between Bile Tolerance and the Presence, of a Ruthenium Red Staining Layer on Strains, of Lactobacillus acidophilus

¹ Department of Food Science and Nutrition, University of Minnesota, St. Paul 56106

Seventeen strains of Lactobacillus acidophilus were evaluated to determine the relationship between bile tolerance and the presence of an outer polysaccharide layer exterior to the cell wall when viewed by transmission electron microscopy. Bile tolerance is necessary for survival of lactobacilli in the intestinal tract, and the polysaccharide layer may be responsible for adherence to human intestinal tissue. These two factors may be the basis for use of L. acidophilus as a dietary adjunct.

Ten strains exhibited a ruthenium red-stained outer polysaccharide layer. Three of the 10 strains had extremely dense layers, which may indicate stronger adherence properties. Seven strains did not contain a ruthenium red-stained outer layer however, six strains that did not have the stained layer were resistant to 1.0% bile concentration. Fourteen strains were tolerant to 1% bile, me strain was tolerant to .6% bile, and two strains were sensitive to bile. No relationship between bile tolerance and the presence of the ruthenium red-stained outer polysaccharide layer was apparent.

Key Words: Lactobacillus acidophilus • adherence • bile tolerance

Submitted on August 6, 1990
Accepted on October 26, 1990