Establishment of oral anaerobes during the first year of life.

Anaerobic species constitute a significant part of the bacterial community of the mouth. Although the time and species involved in the primary colonization of infants are of great importance by forming the basis for further colonization, the development of the oral anaerobic microflora with age is still inadequately understood. In the present study, time and succession of colonization of oral anaerobes were longitudinally examined in 44 healthy Caucasian infants at 2, 6, and 12 months of age. Unstimulated saliva samples were quantitatively cultured on non-selective Brucella blood agar and several selective media for the isolation of anaerobic micro-organisms. The most frequent anaerobic finding in two-month-old infants was Veillonella spp. The Prevotella melaninogenica group also represented early colonizing species, and the frequency increased remarkably during the first year of life, whereas the Prevotella intermedia group organisms seemed to be late colonizers. Fusobacterium nucleatum, non-pigmented Prevotella spp., and Porphyromonas catoniae were occasional findings in subjects at 2 months but frequent findings in those at one year of age. F. nucleatum was the most frequent strictly anaerobic species in one-year-old infants; other fusobacteria were also occasionally found. The frequency of facultative/micro-aerophilic corroding rods and Capnocytophaga spp. started to increase toward the end of the first year. Except for the common presence of facultative/micro-aerophilic Actinomyces spp., other anaerobic gram-positive species were only occasionally present in these infants. Once established, early-colonizing species tended to persist in the mouth. Our longitudinal study demonstrated the establishment of several anaerobic species with steadily increasing frequencies during the first year of life.