Khat and Oral Microbiota. A microbial study with relevance to periodontitis and dental caries
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Khat chewing is a highly prevalent habit in Yemen and East Africa. None of the few studies that investigated the effect of this habit on dental and oral health provides information about its influence on oral microbiota (Paper 1, a review). The aim of the study was to investigate the effects of khat chewing and aqueous khat extracts on a panel of periodontal and cariogenic bacteria, in a step towards better understanding of the relation of the khat chewing habit to periodontitis and dental caries. Materials: A total of 408 plaque samples obtained from 51 khat chewer and non-chewer young males, lyophilized crude aqueous khat extracts made from three cultivars, and a panel of 36 oral microorganisms. Methods: The plaque samples were analyzed by the DNA-DNA checkerboard hybridization method, comparing the prevalence and levels of 14 selected periodontal bacteria in sub- and supragingival plaque samples of khat chewers and nonchewers and of the khat chewing and non-chewing sides (Paper 2). For evaluation of antimicrobial properties of khat, the extracts were tested against 33 oral strains using the agar dilution method of the National Committee for Clinical Laboratory Standards (NCCLS) (Paper 3); in addition, the extracts were tested for their ability to potentiate activity of tetracycline and penicillin G against three resistant isolates (Paper 3). The extracts at various concentrations (0.125-2% w/v) were also evaluated for their effect on key virulence factors of S. mutans: planktonic growth, sucrose-dependent colonization, glucan synthesis, and glucosyltransferases (GTFs) production (Paper 4). Results: Khat chewing increased the prevalence or/and levels of a number of periodontal healthassociated species, while it did not influence, and in some cases decreased, those of periodontal pathogens (Paper 2). Subsequent findings showed that the khat extracts demonstrated selective antimicrobial properties in vitro, with the majority of susceptible strains being periodontal pathogens; the extracts also potentiated the activity of tetracycline and penicillin G against the tested isolates (Paper 3). Concerning the virulence factors of S. mutans, the extracts inhibited formation of adherent biofilms while they enhanced planktonic growth, and inhibited synthesis of both types of glucans while they unregulated GTFs production (Paper 4). Conclusions: Khat chewing does not seem to induce a microbial profile that would put the periodontium at risk of developing disease; it rather favors presence of species that are compatible with periodontal health. This may be attributed, at least in part, to the selective antibacterial properties of khat. Khat also has water-soluble ingredients, probably tannins, with cariostatic properties. In addition, there is preliminary evidence for the presence of resistance –modifying components.
The thesis is based on the following papers, which are referred to in the text by Arabic numerals: 1- Al-hebshi N, Skaug N. Khat (Catha edulis) – an updated review. Addict Biol 2005; 10: 299-307. 2- Al-hebshi N, Skaug N. Effect of khat chewing on selected periodontal bacteria in sub- and supragingival plaque of a young male population. Oral Microbiol Immunol 2005; 20: 141-146. 3- Al-hebshi N, Al-haroni M, Skaug N. Antimicrobial and resistance modifying activities of aqueous crude khat extracts against oral microorganisms. Arch of Oral Biol 2005; in press (Epub Oct 24). 4- Al-hebshi N, Nilsen Ø, Skaug N. In vitro effects of crude khat extracts on the growth, colonization and glucosyltransferases of treptococcus mutans. Acta Odontol Scand 2005; 63: 136-142.
Paper I: Addiction Biology 10, Al-hebshi, Nezar N. & Nils Skaug, Khat (Catha edulis) - an updated review, pp. 299 – 307. Copyright 2005 Society for the Study of Addiction to Alcohol and Other Drugs/. Published by Taylor & Francis AS. Reproduced with permission. Published version. The published version is also available at: http://dx.doi.org/ 10.1080/13556210500353020Paper II: Immunology 20 (3), Al-hebshi, Nezar N. & Nils Skaug, Effect of khat chewing on 14 selected periodontal bacteria in sub- and supragingival plaque of a young male population, pp. 141-146. Copyright 2005 Blackwell Munksgaard. Reproduced with permission. Published version. The published version is also available at: http://dx.doi.org/10.1111/j.1399-302X.2004.00195.xPaper III: Archives of Oral Biology 51(3), Al-hebshi, Nazar; Al-haroni, M. & Nils Skaug, In vitro antimicrobial and resistance-modifying activities of aqueous crude khat extracts against oral microorganisms, pp. 183-188. Copyright 2005 Elsevier Ltd. Reproduced with permission. Published version. The published version is also available at: http://dx.doi.org/10.1016/j.archoralbio.2005.08.001Paper IV: Acta Odontologica Scandinavica 63(3), Al-hebshi Nazar; Nilsen, Ø. & Nils Skaug, In vitro effects of crude khat extracts on the growth, colonization and glucosyltransferases of treptococcus mutans, pp. 136-142. Copyright 2005 Taylor & Francis AS. Reproduced with permission. Published version. The published version is also available at: http://dx.doi.org/10.1080/00016350510019838