Microbial Geography of the Oral Cavity

Although it is assumed that the oral cavity is not homogeneous, total saliva and dental plaque samples are nevertheless routinely used for assessing microbial diversity and its relationship to health and disease conditions. We aimed to determine the bacterial diversity of different oral micro-niches and assess whether saliva and plaque samples are representative of the microbial composition.

Methods:

We have minutely taken samples from each surface of individual teeth and gingival crevices from two healthy volunteers (112 samples per donor), as well as samples from the tongue dorsum, non-stimulated and stimulated saliva. DNA was extracted from each sample and the 16S rRNA gene was amplified by PCR. The resulting PCR products were then pyrosequenced to obtain over 1000 reads per sample, which were taxonomically assigned to obtain a geographic map of bacterial diversity at each tooth and sulcus location.

Results:

The data show considerable differences in bacterial composition between teeth and even between surfaces of the same tooth. The most dramatic differences were observed in incisors and canines, where genera like Streptococcus were found at 40-70% on the vestibular surface but were not detected at all on the lingual side. However, the disparity between the two surfaces disappeared on pre-molar and molar teeth, indicating that the environment gets more homogeneous towards the fauces, and suggesting important gradients of pH, oxygen and temperature influencing bacterial composition. Saliva samples, especially non-stimulated saliva, were not representative of the total diversity of supra- and subgingival plaque.

Conclusions:

We suggest that more precise sampling is required to properly determine oral microbial diversity and to relate that diversity with epidemiological, clinical and etiological parameters. We also propose a set of sampling sites that when pooled will represent the total diversity of sub- and/or supragingival dental plaque more accurately than saliva samples.