Negative correlation between oral malodour and numbers and activities of sulphate-reducing bacteria in the human mouth

The majority of cases of oral malodour are thought to be due to bacterial activities in the mouth, but many of the bacterial species responsible have not been identified. Volatile sulphide compounds have been proposed as constituents of oral malodour. Therefore, the relation between intensity of odour and numbers of bacteria in the mouth that are sulphide-producing from sulphate was investigated. Numbers of such dissimilatory sulphate-reducing bacteria (SRB) and sulphide reduction rates were evaluated in samples from different oral sites in relation to measures of oral malodour. Results showed that sulphate-reducing bacterial numbers and activities were negatively correlated with malodour, as determined by organoleptic assessment and measurement with a sulphide-monitoring instrument, the Halimeter. The data indicate that sulphide produced by oral SRB may not be an important contributor to oral malodour. A rather poor correlation was observed between Halimetric and organoleptic values, indicating that these methods may measure different aspects of oral malodour intensity.