Genetics of sanguinis-Group Streptococci in health and disease

With the application of increasingly advanced "omics" technologies to the study of our resident oral microbiota, the presence of a defined, health-associated microbial community has been recognized. Within this community, sanguinis-group streptococci, comprising the closely related Streptococcus sanguinis and Streptococcus gordonii, together with Streptococcus parasanguinis, often predominate. Their ubiquitous and abundant nature reflects the evolution of these bacteria as highly effective colonizers of the oral cavity. Through interactions with host tissues and other microbes, and the capacity to readily adapt to prevailing environmental conditions, sanguinis-group streptococci are able to shape accretion of the oral plaque biofilm and promote development of a microbial community that exists in harmony with its host. Nonetheless, upon gaining access to the blood stream, those very same colonization capabilities can confer upon sanguinis-group streptococci the ability to promote systemic disease. This article focuses on the role of sanguinis-group streptococci as the commensurate commensals, highlighting those aspects of their biology that enable the coordination of health-associated biofilm development. This includes the molecular mechanisms, both synergistic and antagonistic, that underpin adhesion to substrata, intercellular communication, and polymicrobial community formation. As our knowledge of these processes advances, so will the opportunities to exploit this understanding for future development of novel strategies to control oral and extraoral disease.