Cell surface proteins of encapsulated Streptococcus cremoris: identification and immunochemical characterization

Cell surface proteins of two slime-forming, encapsulated Streptococcus cremoris strains, MLS96 and T5 from the fermented milk product viili, were extracted with the non-ionic detergent Triton X-100. The isolated protein antigens were characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting with antisera produced against whole Strep. cremoris cells. When protein profiles of these strains were compared, seven prominent polypeptides were found common to both and were recognized by both antisera. Five of these polypeptides with molecular weights of 70,000, 54,000, 50,000, 47,000 and 40,000 were identified as cell wall components. The remaining two polypeptides with molecular weights of 42,000 and 26,000 are being studied further in connection with slime formation for which modified Triton X-100 extraction provides a suitable method for isolation of the surface-associated antigens of lactic streptococci.