Bacteria Responsible for Production of the Indole/Skatole Component of Bad Breath

Introduction and objective: Indole and skatole (IS) can be significant contributors to the volatiles responsible for oral malodor. The characteristic smell of IS is recognized even at low concentrations when flossing inflamed interdental sites. Indolepyruvic acid (IPA) is a major intermediate in bacterial tryptophan (trp) degradation. Its deamination results in indole and its decarboxylation in skatole. This study examined the contribution of 13 Gram+ and 12 Gram- representative oral bacteria towards IS production. Methods: Pure cultures of each microorganism at 8.3 % (v/v) were incubated with 6 mM trp or IPA in 60 mM phosphate buffer for 24 h at 37^o C. Head space odor and its VSC content (mostly H₂S) were measured organoleptically and with the Halimeter® (Interscan Corp., CA) at 0, 15 and 30 min and 1,2,3,4 and 24 h. In addition, IS was measured by Kovac's method at the end of each incubation. Results: IS ranged from 0.1 to 15.6 mg/ml of incubate. Overall, 75% of the Gram- bacteria produced 3.1 ±1.5 mg/ml IS compared to 45% of the Gram+ bacteria that produced 0.3±0.1(5) mg/ml IS. B.intermedia, B.gingivalis and F.nucleatum were the major indole producers (15.6, 8.4 and 11.2 mg/ml, respectively). The other Gram negatives produced < 1.0 mg/ml. F.nucleatum produced IS from IPA (4.8 mg/ml), as did H.parainfluenzae II (1.1 mg/ml). Correlation coefficient (r) between IS and organoleptic odor was 0.95. No correlation was observed between VSC measured with the Halimeter and IS. Conclusions: Gram- bacterial dominance of indolic odor production with some Gram+ bacterial participation was supported in this study. Ability of some bacteria to use IPA suggests mixed microbial involvement and contributions. The main IS producing microbes identified are also those strongly associated with periodontal disease. This is consistent with oral malodor and periodontal disease being linked.