Natural history of Streptococcus sanguinis in the oral cavity of infants: Evidence for a discrete window of infectivity

The heterogeneous group of oral bacteria within the sanguinis (sanguis) str eptococci comprise members of the indigenous biota of the human oral cavity , While the association of Streptococcus sanguinis with bacterial endocardi tis is well described in the literature, S, sanguinis is thought to play a benign, if not a beneficial, role in the oral cavity. Little is known, howe ver, about the natural history of S. sanguinis and its specific relationshi p with other oral bacteria, As part of a longitudinal study concerning the transmission and acquisition of oral bacteria within mother-infant pairs, w e examined the initial acquisition of S. sanguinis and described its coloni zation relative to tooth emergence and its proportions in plaque and saliva as a function of other biological events, including subsequent colonizatio n with mutans streptococci. A second cohort of infants was recruited to def ine the taxonomic affiliation of S. sanguinis. We found that the colonizati on of the S. sanguinis occurs during a discrete "window of infectivity" at a median age of 9 months in the infants. Its colonization is tooth dependen t and correlated to the time of tooth emergence; its proportions in saliva increase as new teeth emerge, In addition, early colonization of S. sanguin is and its elevated levels in the oral cavity were correlated to a signific ant delay in the colonization of mutans streptococci. Underpinning this app arent antagonism between S. sanguinis and mutans streptococci is the observ ation that after mutans streptococci colonize the infant, the levels of S. sanguinis decrease. Children who do not harbor detectable levels of mutans streptococci have significantly higher levels of S. sanguinis in their sali va than do children colonized with mutans streptococci, Collectively, these findings suggest that the colonization of S. sanguinis may influence the s ubsequent colonization of mutans streptococci, and this in turn may suggest several ecological approaches toward controlling dental caries.