Streptococcus salivarius is the principal commensal bacterium of the oral cavity in healthy humans. It is the first bacterium which colonizes the dental plaque, before being joined by numerous other species of various genera. It therefore seems to be the pioneer in colonizing dental plaque, creating favorable conditions for the implantation of other species, but also a bacterium which plays the role of moderator, permitting the implantation of bacteria which are harmful to the health of the oral cavity. Finally, this bacterium is sometimes found in opportunistic infections, most commonly after surgical procedures.

It therefore seems important to increase our understanding of this bacterium which interacts with its host in a complex manner. A better knowledge of the molecular and physiologic factors which allow it to colonize dental plaque and to interact with other species will help in designing strategies for the prevention of cavities, especially in children. Furthermore, a knowledge of the characteristics of strains which are isolated in opportunistic infections may help diminish risk by early detection in the most sensitive subjects and in medical personnel.