Relationship between bile tolerance and the presence of a ruthenium red staining layer on strains of Lactobacillus acidophilus

Abstract

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, one 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.