Genetics of sanguinis-group streptococci in health and disease

Our view of oral streptococci has largely been influenced by the approach taken in the last century to identify etiologic agents of disease. As a consequence, beneficial aspects of streptococcal colonization of the oral cavity were initially overlooked. The first comprehensive analysis of the resident oral microbiota was accomplished in 2005 (1), and with this, a new picture began to emerge. With the availability of high-throughput sequencing techniques and an increased sensitivity in analysis methods, the presence of a defined microbiome associated with oral health has been shown (2). Alongside this, “omics” techniques have revealed that prevalent oral diseases such as caries and periodontal disease are polymicrobial in nature and the result of microbial dysbiosis (3, 4). Even more striking, the metabolic output of these mixed microbial communities seems to be more relevant than their precise microbial composition (4). This is also reflected by the fact that the severity of caries and periodontal disease is heavily influenced by the synergistic interactions of the individual members of the polymicrobial consortium, including metabolic cross-feeding and interspecies signaling with transcriptional adjustment to the metabolic output. Thus, the ecological context of the microbial community seems to be of importance to understanding oral health and disease development. As a consequence, polymicrobial diseases cannot be explained by the behavior of one bacterial species and certainly cannot be treated like diseases that follow Koch’s postulates (5 - 7). Novel approaches to combat oral polymicrobial diseases should therefore focus on the bacterial community that is present in the healthy oral cavity. Since oral streptococci are abundant during initial colonization of the tooth (8, 9), their function is to provide a favorable environment for incorporation of later species and to support accretion of the mature oral biofilm, which in general has a health-protecting function (10, 11).