Clonal Distribution of Commensal Streptococci in the Human Oral Cavity

Objectives: Microorganisms colonizing oral soft tissues represent a substantial reservoir for the colonization of teeth, either directly or via saliva. Whilst previous studies have variously assessed the distribution of bacteria in the oral cavity, there is little literature on microbial clonality on various oral tissues. Such data could be used to better understand the process of microbial recolonization after brushing and improve hygiene regimens.
Methods: Oral samples from the buccal mucosa, the dorsum of the tongue, maxillary central incisors and the second mandibular molar fissure were collected from five healthy adults. An unstimulated saliva sample was also collected from each volunteer. Bacteria were isolated from all samples and identified by DNA sequencing using primers targeting the V1-V9 region of bacterial 16S rRNA gene. Sequence analysis identified species with organisms further evaluated for clonality using (GTG)₅repetitive element palindromic polymerase chain reaction (rep-PCR). Bacterial clones were identified using BioNumerics software, in which matching streptococcal isolates had >90% similarity and less than one major band difference
Results: Eight bacterial phyla were identified from all samples and of those identified, 39 genera occurred in all samples from all volunteers. Streptococcus was the most abundant genus within buccal, tooth and tongue samples of all volunteers (predominantly Streptococcus salivarius, Streptococcus sanguinis, Streptococcus mitis,Streptococcus vestibularis and Streptococcus parasanguinis). A total of 98 streptococcal isolates were characterised using (GTG)₅ rep-PCR, of which 64 were an identical clone to at least one other streptococcal isolate. Multiple streptococcal clones were identified on different intraoral tissues of volunteers.
Conclusions: (GTG)₅ rep-PCR fingerprinting identified multiple intra-volunteer streptococcal clones on different intraoral sites of volunteers. Results highlight clonal distribution of oral streptococci across hard and soft oral tissues.