Morphometric parameters, zeta potential and growth rate of Lactobacillus casei Shirota by effect of different bile salts

Effects of primary and secondary bile salts, conjugated to glycine [glycocholic (GCA) and glycodeoxycholic acid (GDCA)], taurine [taurocholic acid (TCA), taurodeoxycholic acid (TDCA)] on morphometry and growth rate of Lactobacillus casei Shirota were studied. Images obtained by scanning electron microscopy showed modification (p < 0.05) in cell minor axis and aspect ratio. The former was modified by GCA while the second by all the bile salts used. The growth rate (μ) values were: 1.95, 0.66, 0.32, 1.89 and 1.86 h^-1 in MRS medium without salts and with GCA, GDCA, TCA and TDCA, respectively. Estimated doubling time was: 0.35, 0.36 and 0.37 h for MRS medium without salts, and with TCA and TDCA, respectively. For GCA and GDCA, a decrease in growth was observed from 4 h and 2 h of incubation, respectively. Bile salt hydrolase activity was determined qualitatively and quantitatively. L. casei Shirota showed activity on taurine-conjugated bile salts. The zeta potential was determined by using the same conditions as those for quantification of bile salt hydrolase activity and different potentials for each dispersion system were found; the zeta potential values were related to the metabolism of L. casei Shirota.