SENSITIVITY OF STREPTOCOCCUS-THERMOPHILUS TO CHEMICAL PERMEABILIZATION

Streptococcus thermophilus cultures were treated with conjugated and u nconjugated bile salts and tested for beta-galactosidase activity, Na- deoxycholate and chenodeoxycholate were more efficient permeabilizing agents than cholate, and all three bile salts were superior to their c orresponding glyco- and tauro-conjugates, Treatment with sodium dodecy l sulfate resulted in the highest measurable beta-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 wa s used to hydrolyze lactose in aqueous solutions and milk.