Study of Normal Flora in the Pharynx of Healthy Children.

To improve our current understanding of normal flora in children, we investigated bacterial isolates from the pharynx and nasopharynx of 173 and 233 healthy children, respectively. The bacterial isolation rates were compared among three age groups: infants (<1 year), toddlers (1-5 years), and school-aged children (6-15 years). Gram-positive cocci were the predominant bacteria in the pharynx (Streptococcus mitis/oralis, 87.3%; Streptococcus salivarius, 54.3%; Rothia mucilaginosa, 41.6%; Staphylococcus aureus, 39.3%). Among infants, S. salivarius and Neisseria subflava, which are related to the development of teeth, were significantly lower than in the other age groups (P <0.0001, S. salivarius; P <0.01, N. subflava). With the exception of Corynebacterium pseudodiphtheriticum (44.2%, gram-positive rods), gram-negative rods largely predominated the nasopharynx (Moraxella catarrhalis, 32.1%; Moraxella nonliquefaciens, 28.3%). Among toddlers, M. catarrhalis and Streptococcus pneumoniae, which are the most common pathogens in acute otitis media, were significantly higher than in the infant group (P <0.05). Among the bacterial species implicated in pediatric respiratory infections, Streptococcus pyogenes was isolated in 3.5% of the pharyngeal samples. S. pneumoniae and Haemophilus influenzae were isolated in 22.3% and 17.2% of the nasopharyngeal samples, respectively. In conclusion, the normal flora of the respiratory tract differs not only by the sampling site but also by the age group.