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Title: Microbial reduction of nitrate to nitrite in the mouth
Author: Duncan, Callum William
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1999
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The aim of this thesis is to determine the mechanisms by which nitrate is reduced to nitrite in the oral cavity and to investigate how these are modulated by environmental, bacteriological and dietary factors in several mammalian species. The rationale is to determine how this system can be augmented to prevent gastrointestinal diseases in humans and other animals. Experiments using chlorate, as an inhibitor of nitrite production, demonstrated that membrane-bound respiratory nitrate reductase enzymes are responsible for nitrate reduction in the mouth. A significant positive correlation was found between nitrite production and nitrite producing bacterial numbers. These bacteria reside in niches that appear to have evolved specifically to provide a low oxygen environment allowing nitrate respiration. Indeed, nitrite production on the tongue dorsum was shown to be sensitive to oxygen tension. Nitrite producing bacteria had colonised the tongues of newborn rats by 4 days of age and adult levels of nitrate reductase activity were achieved by weaning. Thus, protection against enteric pathogens develops from an early age. Rats and pigs reared in a very "clean" environment had a much lower capacity to produce nitrite than animals exposed to a larger and more diverse microbial flora. Exposure to a high nitrate diet markedly enhanced oral nitrite production. In conclusion the present work shows that nitrate is reduced to nitrite in the oral cavity by symbolic nitrate-reducing facultatively anaerobic staphylococci, using respiratory membrane-bound nitrate reductase. These bacteria reside in specific areas of the oral cavity. This capacity is acquired from an early age and is dependent on the rearing conditions so that free-range animals have a more active nitrite production, particularly if they consume a high nitrate diet. The results presented in this thesis can be used to set up a large scale animal trial to determine the antimicrobial effect in vivo.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available