The consistent application of hydrogen peroxide controls biofilm growth and removes Vermamoeba vermiformis from multi-kingdom in-vitro dental unit water biofilms

The water systems inside a dental unit are known to be contaminated with a multi-kingdom biofilm encompassing bacteria, fungi, viruses and protozoa. Aerosolization of these micro-organisms can potentially create a health hazard for both dental staff and the patient. Very little is known on the efficacy of dental unit disinfection products against amoeba. In this study we have examined the effect of four different treatment regimens, with the hydrogen peroxide (H₂O₂) containing product Oxygenal, on an in-vitro multi-kingdom dental unit water system (DUWS) biofilm. The treatment efficacy was assessed in time using heterotrophic plate counts, the bacterial 16S rDNA, fungal 18S rDNA gene load and the number of genomic units for Legionella spp. the amoeba Vermamoeba vermiformis. The results indicated that a daily treatment of the DUWS with a low dose H₂O₂ (0.02% for 5 h), combined with a weekly shock dose (0.25% H₂O₂, 30 min) is necessary to reduce the heterotrophic plate count of a severely contaminated DUWS (>10⁶ CFU.mL⁻¹) to below 100 CFU.mL⁻¹. A daily treatment with a low dose hydrogen peroxide alone, is sufficient for the statistically significant reduction of the total amount of bacterial 16S rDNA gene, Legionella spp. and Vermamoeba vermiformis load (p < 0.005). Also shown is that even though hydrogen peroxide does not kill the trophozoite nor the cysts of V. vermiformis, it does however result in the detachment of the trophozoite form of this amoeba from the DUWS biofilm and hereby ultimately removing the amoeba from the system.