Streptococcus in Oral Cavity of Infants: Infectivity

The heterogeneous group of oral streptococci comprising the sanguinis streptococci are members of the human indigenous biota. (The previously recognized species of the genus Streptococcus named “sanguis” has recently been changed to “sanguinis” so as to conform to the rules of Latin grammar [32]). S. sanguinisis recognized not only for its historical association with life-threatening bacterial endocarditis, but also because of its putative antagonistic role in dental caries [20] and periodontal diseases [27]. In terms of the former, S. sanguinis may compete with the mutans streptococci for colonization sites on tooth surfaces, since both groups of bacteria require the presence of teeth for colonization [6,7] and may exhibit direct biochemical antagonism in situ [33]. Because the cariogenic potential of S. sanguinis is deemed low compared to that of the mutans streptococci, several investigators have suggested that the S. mutans/S. sanguinis ratio may serve as an indicator for caries risk, i.e., the smaller the ratio, the lesser the risk of caries [12,19,20]. In another study, however, a caries-predictive role for the S. mutans/S. sanguinis ratio could not be demonstrated [3]. Carlsson and coworkers were among the first to describe both the taxonomic and ecological features of S. sanguinis in the oral cavity [4-7]. In fact, it was the Carlsson group that made the key observation that S. sanguinis did not colonize infants until after the emergence of teeth [7] and that colonization by S. sanguinis precedes that by mutans streptococci. As part of a longitudinal study involving the acquisition of indigenous oral microbes in an infant population, the aim of the present study was to determine when S. sanguinis is acquired by infants and whether this acquisition period is discrete, as in the case of the mutans streptococci [8]. Since oral colonization with S. sanguinis precedes that with mutans streptococci, it seems reasonable to speculate that the former event may influence the latter, especially considering that the colonization site of both organisms is tooth surfaces. Accordingly, we wanted to explore the relationship between the temporal and quantitative aspects of colonization by S. sanguinis in relation to subsequent colonization by mutans streptococci. Here, we show that infants acquire S. sanguinis during a discrete “w