A longitudinal study of Streptococcus mutans colonization in infants after tooth eruption.

We previously reported that, before tooth eruption, over one-half of infants aged 6 mos were already infected with Streptococcus mutans. The aim of this investigation was to determine the colonization of S. mutans after tooth eruption in the same cohort of 111 infants (35 pre-term, 76 full-term). Our results showed that S. mutans colonization increased with increasing age, so that by 24 mos of age, 84% harbored the bacteria (p < 0.01). The mean and median ages of S. mutans colonization in dentate infants were 15.7 mos and 16.0 mos, respectively. Factors associated with S. mutans colonization were sweetened fluids taken to bed (p < 0.01), frequent sugar exposure (p < 0.03) and snacking (p < 0.03), sharing of foods with adults (p < 0.03), and maternal S. mutans levels of > 10(5) CFU/mL (p < 0.02). In contrast, non-colonization of S. mutans was associated with toothbrushing (p < 0.03) and multiple courses of antibiotics (p < 0.001). Analysis of our data establishes the timing of S. mutans colonization in children from birth to 24 mos of age.