Probiotic properties of Lactobacillus strains isolated from Tibetan kefir grains

Abstract

The objective of this study was to evaluate the functional properties of lactic acid bacteria (LAB) isolated from Tibetan kefir grains. Three Lactobacillus isolates identified as Lactobacillus acidophilus LA15, Lactobacillus plantarum B23 and Lactobacillus kefiri D17 that showed resistance to acid and bile salts were selected for further evaluation of their probiotic properties. The 3 selected strains expressed high in vitro adherence to Caco-2 cells. They were sensitive to gentamicin, erythromycin and chloramphenicol and resistant to vancomycin with MIC values of 26 µg/ml. All 3 strains showed potential bile salt hydrolase (BSH) activity, cholesterol assimilation and cholesterol co-precipitation ability. Additionally, the potential effect of these strains on plasma cholesterol levels was evaluated in Sprague-Dawley (SD) rats. Rats in 4 treatment groups were fed the following experimental diets for 4 weeks: a high-cholesterol diet, a high-cholesterol diet plus LA15, a high-cholesterol diet plus B23 or a high-cholesterol diet plus D17. The total cholesterol, triglyceride and low-density lipoprotein cholesterol levels in the serum were significantly (P<0.05) decreased in the LAB-treated rats compared with rats fed a high-cholesterol diet without LAB supplementation. The high-density lipoprotein cholesterol levels in groups B23 and D17 were significantly (P<0.05) higher than those in the control and LA15 groups. Additionally, both fecal cholesterol and bile acid levels were significantly (P<0.05) increased after LAB administration. Fecal lactobacilli counts were significantly (P<0.05) higher in the LAB treatment groups than in the control groups. Furthermore, the 3 strains were detected in the rat small intestine, colon and feces during the feeding trial. The bacteria levels remained high even after the LAB administration had been stopped for 2 weeks. These results suggest that these strains may be used in the future as probiotic starter cultures for manufacturing novel fermented foods.

Figure 1. Adhesion ability of Lactobacillus isolates to Caco-2 epithelial cells compared with the reference strain Lactobacillus rhamnosus GG (LGG).

The presented values are the means of triplicate determination, and the different letters (a, b) represent significant differences (P<0.05).

Figure 2. Total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) levels in the serum of rats fed a high-cholesterol diet alone (control) or supplemented with different lactic acid bacteria strains (LA15, B23 or D17) for 4 weeks.

The results are expressed as the means ± standard deviation, n = 10. Means within the same lipid series with different lowercase letters (a-d) are significantly different (P<0.05).

Figure 3. Fecal cholic acid concentrations in rats fed a high-cholesterol diet alone (control) or supplemented with different lactic acid bacteria strains (LA15, B23 or D17) for 4 weeks.

The results are expressed as the mean ± standard deviation. Mean values with different letters (a, b, c) differ significantly (P<0.05).