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

Abstract

The heterogeneous group of oral bacteria within the sanguinis (sanguis) streptococci comprise members of the indigenous biota of the human oral cavity. While the association of Streptococcus sanguinis with bacterial endocarditis 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, however, about the natural history of S. sanguinis and its specific relationship with other oral bacteria. As part of a longitudinal study concerning the transmission and acquisition of oral bacteria within mother-infant pairs, we examined the initial acquisition of S. sanguinis and described its colonization relative to tooth emergence and its proportions in plaque and saliva as a function of other biological events, including subsequent colonization with mutans streptococci. A second cohort of infants was recruited to define the taxonomic affiliation of S. sanguinis. We found that the colonization 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 dependent and correlated to the time of tooth emergence; its proportions in saliva increase as new teeth emerge. In addition, early colonization of S. sanguinis and its elevated levels in the oral cavity were correlated to a significant delay in the colonization of mutans streptococci. Underpinning this apparent antagonism between S. sanguinis and mutans streptococci is the observation 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 saliva than do children colonized with mutans streptococci. Collectively, these findings suggest that the colonization of S. sanguinis may influence the subsequent colonization of mutans streptococci, and this in turn may suggest several ecological approaches toward controlling dental caries.

FIG. 1

Window of infectivity for S. sanguinis. Infants became colonized by S. sanguinis at a median age of 9.0 months. Colonization followed the emergence of primary teeth; the first tooth emerged at a median age of 7.1 months.

FIG. 2

Relationship between the age at first tooth emergence and colonization of the infant by S. sanguinis. MS, mutans streptococci. The correlation was statistically significant (r = 0.64, P = 0.0001).

FIG. 3

Study design of the natural history study: sampling periods relative to the infant time line. Bacteriological samples were taken at 3-month intervals. Pre- and post-mutans streptococci levels of S. sanguinis/total cultivable bacteria in saliva were averaged and compared relative to the time to colonization by the mutans streptococci.

FIG. 4

Cumulative probability of infection by S. sanguinis in 45 infants. Data from the present study (▵) are compared to data extrapolated from the study of Carlsson and coworkers (○) (7).