The matrix substances in the walls of Gram-positive bacteria may be polysaccharides or teichoic acids. Teichoic acids are of two main types-Ribitol teichoic acids and glycerol teichoic acids. These acids are polymers of ribitol phosphate and glycerol phosphate respectively. Only one type is found in the wall of any particular strain of Gram-positive bacteria. Teichoic acids form acceptor sites for bacteriophages and at least same of them are located on the surface in many Gram-positive bacteria.