Establishment and distribution of the bacteria Actinomyces viscosus and Actinomyces naeslundii in the mouths of monkeys (Macaca fascicularis).

The colonization of the mouth by the two Actinomyces species, postulated to be members of a basic plaque flora, was studied in 27 consecutively-born neonatal monkeys. Bacteria adherent to the tongue and cheek surfaces were sampled from each monkey soon after birth (mean age = 3.2 days). The tongue and cheek surfaces and the labial surfaces of the incisor teeth were sampled at 4, 8 and 12 weeks of age. From only one neonatal sample were Actinomyces species isolated. By 4 weeks of age, the incisor teeth are partially erupted and, from teeth erupted more than 1 mm, A. naeslundii was frequently isolated and its proportion increased between 4 and 8 weeks on all surfaces sampled. At 4, 8 and 12 weeks, the proportion of A. naeslundii on the incisor teeth was greater than on the mucosal surfaces. The isolation rate of A. viscosus was low in these neonates, but it was isolated from each of 6 juvenile monkeys fed a starch diet. In the 6 juvenile monkeys, the proportion of A. viscosus decreased following the introduction of a sucrose-containing diet, whereas the proportion of A. naeslundii on the teeth increased. The early establishment of A. naeslundii and, to a lesser extent, A. viscosus in the dental plaque of neonatal monkeys fed exclusively by their mothers suggests that members of a basic plaque flora may be those bacteria establishing in the plaque during the period of breast-feeding.