Comparative preparation methods of sialylated capsule antigen from Streptococcus suis type 2 with type specific antigenicity

The capsular polysaccharide (CPS) of Streptococcus (S.) suis type 2 was isolated from a type strain of S. suis NCTC 10234 by three different preparative methods: (A) lysozyme treatment method, (B) autoclave extraction method, and (C) HCl-extraction method. The structural characteristics of the three CPS (CPS-A, B and C) were examined by gel permeation chromatography, reactivity against rabbit antiserum and proton-nuclear magnetic resonance (¹H-NMR). N-Acetylneuraminic acid (NeuAc) residues as sialic acid in CPS-C were partially dissociated or degraded during preparation with a remarkable decrease in the molecular mass and the antigen activity. Although both methods A and B produced intact CPS without releasing NeuAc residues, method B was considered to be a more suitable procedure for preparing the CPS antigen because of time-saving and safety factors. Sugar analysis by high performance liquid chromatography and gas liquid chromatography showed that CPS-B consisted of five kinds of sugars: Rhamnose (Rha), Glucose (Glc), Galactose (Gal), N-acetylglucosamine (GlcNAc) and NeuAc, in a molar ratio of 1.00:0.95:3.68:0.80:1.31. After complete removal of NeuAc residues by mild acid hydrolysis of CPS-B, the reactivity with anti-type 2 serum was not detected. The NeuAc residue in CPS of S. suis type 2 strain was thought to be the antigen epitope portion.