A vaccine, comprising as antigen, at least a part of the cell of strains of Streptococcus sanguis having a high pathogenic potential and capable of decomposing raffinose and mellibiose, in association with a pharmaceutically acceptable carrier or excipient. Preferably, the antigen is derived from the pili-like structures on the surface layer of the cells. Antibodies produced by immunizing a mammal with said antigen to produce the corresponding antibodies in the body of said mammal and recovering the resultant antibodies from the mammal. A pharmaceutical composition, comprising as active ingredient said antibodies, in association with a pharmaceutically acceptable carrier or excipient. Said vaccine, antibodies and antibody-containing composition may be used for treating human and animal diseases caused or aggravated by said microorganisms such as MCLS. Preferably, the composition comprises antibodies produced by the use of antigen(s) derived from the pili-like structures, in association with a carrier or excipient suitable for oral administration. The preferred composition may be directly and safely administered to the oral cavity of humans and animals to prevent or at least inhibit the infection of the virullent strains with good results.