Inhibition of Hydrogen Sulphide in Oral Bacteria by Mouth Rinses

Objectives: Oral malodour is associated with increased production of volatile sulphur compounds, of which hydrogen sulphide (H₂S) is a major component. This study evaluates the anti-malodour effects of a cetylpyridinium chloride (CPC) containing mouthwash (Colgate Total Advanced Health™) versus a fluoride-containing mouthwash (Colgate FluoriGard™ Daily Rinse) through the inhibition of hydrogen sulphide production, using a microdilution assay system.
Methods: Porphyromonas gingivalis, Fusobacterium nucleatum and mixed oral bacteria (saliva) were grown in microtiter plates containing serially diluted concentrations of Total Advanced Health or FluoriGard at 37°C, for 48 h under anaerobic conditions. To determine H₂S production, 20µl of 0.3% L-cysteine and 20µl of 1.2% lead acetate were added to each well and the plates incubated anaerobically at 37°C for a further 24 h. Plates were scored based on the presence or absence of a black precipitate, indicative of H₂S production. The lowest concentration of mouthwash that inhibited H₂S production, as noted by the absence of the black precipitate, was defined as the minimum hydrogen sulphide inhibitory concentration (MHIC).
Results: Differences in the ability to inhibit H₂S production were noted for each of the mouthwashes tested. The CPC mouthwash was statistically significantly (p<0.05) more effective than the fluoride mouthwash. MHICs of 0.14% ± 0.05%, 1.17% ± 0.59% and 0.8% ± 0.0% for P. gingivalis, F.nucleatum and the mixed oral bacterial sample were obtained using Total Advanced Health, respectively. In contrast, the MHIC’s for the FluoriGard mouthwash for P. gingivalis, F. nucleatum and the mixed oral bacterial sample were 2.76% ± 0.68%, 22.22% ± 5.51% and 25% ± 0.0%, respectively.
Conclusions: The microdilution assay employed during this study was effective at assessing and comparing the relative anti-malodour effects of two different mouthwash formulations based on visual observations of the black precipitate formed. The CPC mouthwash demonstrated significantly greater inhibition of hydrogen sulphide than the control mouthwash.