Defining oral microbiological health

Abstract

Background: The composition of the oral microbiota in periodontal health and the microbial changes associated with the early stages of gingivitis are poorly defined. Aims: The aims of this work were to: (i) characterise the bacterial composition of dental plaque in subjects with experimentally-induced gingivitis; (ii) identify candidate oral probiotic taxa; (iii) evaluate alternative approaches for oral Neisseria spp. differentiation. Methods: Twenty volunteers abstained from oral hygiene in the mandible for two weeks. Clinical indicators of inflammation were monitored and samples of plaque were analysed, together with 20 control samples from periodontitis patients, by pyrosequencing of 16S rRNA genes and culture. A panel of oral bacterial isolates were screened for inhibition of six indicator organisms using a deferred antagonism assay. Sequencing of seven ‘housekeeping’ genes and a ribosomal protein gene (rplF) were evaluated as methods to differentiate Neisseria species. Results: All volunteers developed gingivitis after two weeks. 344,267 16S rDNA sequences were clustered into a median of 299 species-level Operational Taxonomic Units (OTUs) per sample. Principal Coordinate Analysis plots revealed shifts in community structure with gingivitis development, and the mean Simpson’s inverse diversity index increased from 32 at baseline to 47.5 after two weeks (P<0.0001). Fusobacterium nucleatum subsp. polymorphum, Lautropia sp. HOTA94, Lachnospiraceae sp. HOT100 and Prevotella oulorum were significantly associated with gingivitis, whilst Rothia dentocariosa was health-associated. Of 80 isolates screened, two strains of Streptococcus cristatus and a Streptococcus sp. HOT071 strain, inhibited the growth of one or more of Streptococcus anginosus, Solobacterium moorei, Porphyromonas gingivalis and Filifactor alocis. rplF gene sequences were found to reliably differentiate oral Neisseria species, although some taxonomic revision to the genus is indicated. Conclusions: A highly species-rich bacterial community in health-associated plaque was revealed and new health- and gingivitis-associated taxa were identified. Three strains were found with potential for use as oral probiotics.

Date of Award	2014
Original language	English
Awarding Institution	King's College London
Supervisor	William Wade (Supervisor) & Veronica Booth (Supervisor)