From Babies to Retirement: What microbes lurk in our mouths?

Objectives: To characterise, by next-generation DNA sequencing technology, the bacterial diversity in humans at different stages of life in both health and disease.

Methods: Samples from five intraoral sites were taken from 28 participants in eight age groups: 10-12 months, 2-3 years, 4-5 years (with and without caries), 6-7 years, 13-15 years, 20-25 years, 40-50 years and >65 years. Bacterial 16S rRNA genes were PCR-amplified from each sample and sequenced using the GS‑FLX Titanium pyrosequencer. All sequence data was processed using CLOTU.

Results: Analysis of the bacterial diversity in all oral samples revealed the presence of only 40 to <200 distinct species with age-dependent species distribution being observed. Gram-positive species (e.g., Streptococcus) were predominantly detected on the dental surfaces in infants, which shifted to a more Gram-negative profile (e.g., Leptotrichia, Fusobacterium) in older age groups. The adolescent group (13-15 years) appeared to be a critical point after which bacterial profiles were dominated by genera such as Capnocytophaga, Porphyromonas and Prevotella. The genus Rothia was hardly detected in adults, suggesting that it may be child-specific. Comparison of the bacterial species between children with and without dental caries revealed significant upward shifts in the populations of Streptococcus. However, the prevalent streptococcal species in children with caries was not Streptococcus mutans but Streptococcus sanguinis, a finding that merits further investigation.

Conclusions: Despite a limited range of species overall, age-dependent shifts in oral bacterial diversity were evident at different stages of life with some genera being detected only in certain age groups, e.g., Rothia (children). Furthermore, the presence of under-studied genera such as Lachnospiraceae and Leptotrichia demonstrate the need to elucidate their ecological roles in the oral cavity.