A branched polysaccharide derivative composed of a backbone of repeating beta-D-Gal-(1->4)-beta-D-Glc-(1->6)-[alpha-Neu5Ac-(2->3)-beta-D-Gal-(1->4)]-beta-D-GlcNAc units, joined by (1->3)-linkages as shown. Group B Streptococcus (GBS) type III capsular polysaccharide.