Abstract
Periodontitis is associated with shifts in the balance of the subgingival microbiome. Many species that predominate in disease have not been isolated from healthy sites, raising questions as to the origin of these putative pathogens. The study aim was to determine whether periodontal pathogens could be enriched from pooled saliva, plaque and tongue samples from dentally-healthy adult volunteers using growth media that simulate nutritional aspects of the inflamed subgingival environment. The microbiome was characterised before and after enrichment using established metagenomic approaches, and the data analysed bioinformatically to identify major functional changes. After three weeks, there was a shift from an inoculum in which Streptococcus, Haemophilus, Neisseria, Veillonella and Prevotella species predominated to biofilms comprising an increased abundance of taxa implicated in periodontitis, including Porphyromonas gingivalis, Fretibacterium fastidiosum, Filifactor alocis, Tannerella forsythia, and several Peptostreptococcus and Treponema spp., with concomitant decreases in health-associated species. Sixty-four species were present after enrichment that were undetectable in the inoculum, including Jonquetella anthropi, Desulfovibrio desulfuricans and Dialister invisus. These studies support the Ecological Plaque Hypothesis, providing evidence that putative periodontopathogens are present in health at low levels, but changes to the subgingival nutritional environment increase their competitiveness and drive deleterious changes to biofilm composition.
Highlights
The mouth harbours a diverse and natural microbiota that persists on oral surfaces as structurally- and functionally-organised multi-species biofilms that have a symbiotic relationship with the host[1,2]
Pooled oral bacterial samples from eight volunteers were subjected to enrichment culture in two types of medium for three weeks, and the microbial composition and potential functions were compared between biofilms enriched on these different media and between the biofilms and the inoculum
The oral microbiome exists as complex multi-species biofilms on oral surfaces, especially on teeth, and oral hygiene can maintain dental plaque at levels compatible with health
Summary
The mouth harbours a diverse and natural microbiota that persists on oral surfaces as structurally- and functionally-organised multi-species biofilms that have a symbiotic relationship with the host[1,2]. The frequent intake of fermentable dietary sugars and/or reductions in saliva flow result in dental biofilms experiencing extended periods of low pH This selects for acidogenic/ acid-tolerating species at the expense of beneficial oral bacteria that preferentially grow at neutral pH5,6, and increases the risk of dental caries. The factors that drive the changes in the microbiota in periodontal disease are not fully understood, and a number of theories have been postulated to explain the shift from a symbiotic to a dysbiotic relationship with the host These theories range from exogenous infection[13], co-infection with viruses[14], enrichment of minor species within the biofilm following changes to the local environment[15] through to low abundance keystone pathogens orchestrating commensal species to provoke a destructive inflammatory response[16], but experimental evidence for these concepts is sparse. Tongue and supragingival plaque from the volunteers were pooled to increase the probability of including putative periodontal pathogens in the inoculum prior to enrichment
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