Abstract: The present invention belongs to the field of the biotechnology, and relates to novel Streptococcusbacteria which are useful as antimicrobial agents, particularly against caries and periodontal disease. The invention relates to compositions and functional food comprising the novel bacteria. In particular, the present invention relates to a novel bacterial strain, deposited at the Colección Española de Cultivos Tipo, with accession number CECT 9174, which has proven to be useful in the prevention and treatment of caries and periodontal disease.