Anaerobes in the upper respiratory tract in infancy.

Development of the indigenous microbiota begins on the surfaces of the human body after birth when infants are exposed to continuous person-to-person and environmental contacts with microbes. Anaerobes constitute a significant part of indigenous bacterial communities at different body sites. Pioneering anaerobic commensals are able to colonize and survive in the oral cavity during the first months of life. After teeth emerge, more attachment sites and potential niches are available for anaerobic bacterial colonization. Specific partner relationships influence the composition and stability of forming multigeneric communities, biofilms, where Fusobacterium nucleatum is of specific interest. In infancy, the oral colonization seems to be rather stable at species level, though not at clonal level. The colonization pattern in the nasopharynx is different from that in the oral cavity; anaerobes are absent from healthy nasopharynges but transiently colonize this anatomical site during infection. The most plausible origin for nasopharyngeal anaerobes is the oral cavity and, conceivably, saliva is the most likely transmission vehicle. Whether anaerobic bacteria colonize the nasopharynx just because of ecological changes favoring their growth or whether they could play an active role in the pathogenesis of respiratory infections is not known.