Sensitivity of Streptococcus thermophilus to Chemical Permeabilization

Streptococcus thermophilus cultures were treated with conjugated and unconjugated bile salts and tested for β-galactosidase activity. Na-deoxycholate and chenodeoxycholate were more efficient permeabilizing agents than cholate, and all three bile salts were superior to their corresponding glyco- and tauro-conjugates. Treatment with sodium dodecyl sulfate resulted in the highest measurable β-galactosidase levels in permeabilized cells, whereas response to Triton X-100 was variable and strain dependent. Na-deoxycholate, chenodeoxycholate, and sodium dodecyl sulfate caused cell injury and arrested culture growth for 4 h or longer. The nongrowing permeabilized biomass of S. thermophilus was used to hydrolyze lactose in aqueous solutions and milk.