The Anaerobic Microflora: The Accused in Oral Malodour?

Nandita Shenoy, Junaid Ahmed, Arjun T, Vidya Pai, Almas Binnal


Background: Oral malodour is foul-smelling breath from the oral cavity and is due to metabolic products of bacteria in the oral cavity but can also be caused by many other systemic diseases. Oral malodour is believed to originate from foul-smelling gases, such as hydrogen sulfide produced by oral bacteria. Aim: To identify hydrogen sulfide producing bacteria from tongue biofilm and to investigate the relationship between bacterial flora and hydrogen sulphide levels in the oral cavity. Materials and Methods: Oral malodour levels in 26 subjects (age 16-69 years) were assessed by portable volatile sulfide monitor Halimeter and gas chromatography. They were accordingly divided into two groups: an odour group and a no/low odour group. Tongue coatings were sampled and organisms were categorized. Results: Tongue coatings were spread onto sheep blood agar (anaerobic) containing Casein enzymic hydrolase, Papaic digest of soyabean meal, yeast extract, sodium chloride, L-cysteine, Hemin, and Agar at final pH (at 250C) 7.4±0.2. The plates were incubated at 370C for 48-72hrs aerobically and anaerobically in anaerobic chamber with mixed gas supply. Bacteria forming black or grey colonies were selected as hydrogen sulphide-producing phenotypes. The numbers of total bacteria (P < 0.05) and hydrogen sulphide-producing bacteria (P < 0.05) in the odour group were significantly larger than those in the no/low odour group. Species of Veillonella, Prevotella, Bacteriods and Peptostreptococcus were the predominant hydrogen sulphide-producing bacteria in odour group and low in no/low odour group. Conclusion: These results suggest that an increase in the number of hydrogen sulphide-producing bacteria in the tongue biofilm is responsible for oral malodour, although the bacterial composition of tongue biofilm did not differ between the two groups.


Oral malodour; Halimeter; Hydrogen sulphide; Oral malodor measurement; Volatile sulphur compounds; Tongue coating; Tongue biofilm; Microorganisms

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