Rapid Griess assay (RGA): a chairside test for ex vivo semi-quantitative oral nitrite measurement and in vitro assessment of nitrite production by oral bacteria.

Background: Nitrite (NO₂ ^-) is produced through enzymatic reduction of dietary nitrate (NO₃ ^-) by oral bacteria: a process contributing to cardiovascular - and possibly oral - health. NO₂ ^- quantitation in biological samples is a complex exercise, and available methods are not well-adapted for chairside use. Therefore, we aimed to develop and evaluate a semi-quantitative chairside test for NO₂ ^- in oral samples. We also evaluated NO₂ ^- generation in several bacterial species in vitro.

Materials and methods: From 12 healthy individuals, tongue, saliva and plaque samples were collected and evaluated chairside across 4 weeks, using the rapid Griess assay (RGA). The RGA was further used to test bacterial species for NO₂ ^- production.

Results: In saliva, plaque and tongue samples, low, variable and high NO₂ ^- levels, respectively, were found. Tongue samples were the most stable over time. High and medium NO₂ ^- production capacities were shown by Actinomyces spp. (including Schaalia odontolytica), Veillonella parvula, and Rothia spp. RGA results were reproducible.

Conclusion: The RGA provided stable and reliable results for chairside NO₂ ^- semi-quantitation, and revealed elevated and stable NO₂ ^- levels on the tongue. In vitro, bacterial NO₂ ^- production was consistent with the available literature, but uncertainty remains regarding Neisseria spp. Our results showed promise for clinical and research applications of the RGA.