Clinical significance of <i>Streptococcus</i> members in developing periodontitis

Bacteria of the genus Streptococcus are one of the most numerous and diverse representatives in the normal biocenosis of human organs and systems particularly being abundant as obligatory inhabitants of the oral cavity. All streptococci are divided into six groups: S. mitis, S. anginosus, S. salivarius, S. mutans, S. bovis and S. pyogenes, among which their certain number may potentially participate in the infectious process of developing periodontitis. Owing to the presence of a wide range of adhesion, invasion and colonization factors, they are capable of performing a protective function such as colonization resistance, but they may also cause formation of a pathological process in the tooth tissues and dento-facial system. The most prominent adhesion factors are antigens I/II (Ag I/II), fibronectin, collagen, laminin, fibrinogen binding proteins, serine-rich glycoproteins, pili, protein M, proteases, C5a peptidases, and the presence of a tooth capsule. Among the complex of proteolytic enzymes, it is important to note that streptococci contain enzymes hyaluronidase and lyase, which cleave the β1,4 bond between N-acetylglucosamine and d-glucuronic acid as the components of hyaluronic acid being a part of the connective tissues. The members of the S. anginosus group are able to release chondroitin sulfatase, which destroys chondroitin sulfates as specific components in cartilage, ligaments and other connective tissue structures. The enzymes noted contribute to a deeper spread of microorganisms in host tissues. Pathological processes associated with the development of periodontitis comprise a complex problem, wherein several important elements take part, including an infectious agent, a macroorganismal response in the form of nonspecific and adaptive immunity, as well as involvement of anti-inflammatory components. A great number of studies in research literature are dedicated to describe to participation of the members within the “red”, “orange” and “green” complexes as the principal components in developing periodontitis. Whereas the “yellow” and the “purple” complex play a more protective role by acting as antagonists while interacting with periodontopathogens, but it should not be ruled out a potential participation for some representatives, particularly S. intermedius, S. gordonii, A. odontolyticus, A. naeslundii in developing periodontal disease. Altogether, it poses a problem, which may be solved solely based on a multidisciplinary approach by inviting not only dentists and bacteriologists but also researchers of other specialties. Here we review the studies found in international and national data bases such as Scopus, Web of Science, Springer, RSCI.