Effect of mouth-rinse formulations on oral malodour processes in tongue-derived perfusion biofilm model

An in vitro matrix biofilm perfusion model of tongue-derived microcosms for studying volatile sulfur compound (VSC) biogenesis has been previously described. The model was modified in order to monitor H₂S in situ by use of a specialized electrode assembly based on microbial fuel cell technology. This system was designed to give real-time measurements expressed as electrode power output, which were proportional to H₂S levels, measured by other means. In addition to the model modifications, the aim of this study was to demonstrate the biofilm responses following single or multiple exposure to biocidal, biostatic or VSC-inhibiting active compounds used in products. Tongue-derived biofilms (n = 6 per experiment) were perfused with one-fifth strength BHI at 20 ml h⁻¹ pH 7.2 and pulsed with putative treatment agent, placebo and controls including Zn²⁺ ions and chlorhexidine (CHX). Compared with their pre-treatment conditions, all biofilms responded to the treatments in terms of reductions in hydrogen sulfide generation (as detected by the biofilm-electrode response) and other microbial volatile organic compounds (VOCs) as detected using a selected ion flow tube mass spectrometry analyser. The microbiological analysis of the treated and control biofilms show that test products (formulations with active agents) all gave reduced cell populations compared to the control biofilm. An order of effects (magnitude and duration) suggests that both the test agent and CHX produced the strongest reductions, distinct from the responses obtained for the placebo and water controls, which were largely similar. It is concluded that the in vitro perfusion model may be used to replicate many of the activities and reactions believed to be occurring by the tongue biofilm microflora within a real mouth, including H₂S and VOC biogenesis and their inhibition by exposure to active agents.