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Title: Selection, interaction and adaptation in the oral microbiota
Author: Glancey, Andrea
ISNI:       0000 0004 2717 6786
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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The mechanisms that underlie the stability and inter-individual variation of oral microbial communities are currently not well understood. The research described in this thesis represents a series of investigations with the unifying aim to better understand the processes which influence the structure, microbiological composition and temporal compositional stability of the oral microbiota. Studies of intra and inter-individual interactions between oral isolates and whole microcosms described in this thesis (Chapters 5 and 6) investigated these processes and additionally provide information which will contribute to the development of more realistic in vitro models. Bacteria were isolated from the saliva of four individuals and a modified cross-streak method used to determine positive, negative or neutral interactions among strains in all possible pair-wise combinations. Sorbarod microcosms were established with saliva from the same four volunteers which were then profiled using differential bacterial counting and PCR-DGGE to determine community relatedness, diversity and stability. The incidence of negative interactions was significantly higher than were positive interactions for both self/self and self/non-self pairings. Combining saliva in the Sorbarods resulted in unique oral microcosms, distinct from the progenitor populations, which exhibited reduced stability and decreased species diversity. Therefore oral bacteria appear to have developed mechanisms to compete against those organisms from which they derive no benefit and cooperate with a limited number of species. Compositional stability and inter-individual variation may result from stochastic events during consortial development together with various host-derived and environmental variables. Using the pooled saliva of two or more individuals as inocula for microcosm experiments may therefore result in unrepresentative modelling. Chapter 3 compares effects of exposure to a triclosan-based dentrifice (TD) and a stannous fluoride-based dentrifice (SZD) on bacterial growth, acid production and bacterial composition in salivary-derived biofilm communities. A preliminary screening method was used to assess the effects on bacterial viability and acidogenesis whilst PCR-DGGE was utilised to determine the effects on bacterial composition of the salivary consortia. Exposure to either dentrifice for 16h caused reductions in microbial diversity and resulted in the emergence of distinct community profiles, which were most marked for TD. TD more potently inhibited bacterial growth and acid production than did SZD. In Chapter 4 the frequency and strength of coaggregation between and among human oral and intestinal bacteria was assessed. Ten oral and ten enteric species were tested using a spectrophotometric coaggregation assay in all possible pair-wise combinations. Oral strains were the most polygamous coaggregators whilst strong interactions between oral and gut strains were considerably less common. Coaggregation scores were also low between members of the intestinal microbiota which indicates that the processes of coaggregation and coadhesion are not as important in the formation of intestinal biofilms as they are in the oral cavity. Heating and sugar inhibitor experiments indicated that, similar to oral microorganisms, interactions with intestinal and oral strains were lectin-carbohydrate based.
Supervisor: Mcbain, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available