Ex vivo inhibition of enamel phosphate uptake in Rothia dentocariosa

Introduction. Oral bacteria, such as Rothia dentocariosa (Rd), can modulate external aqueous phase orthophosphate (P_i) concentrations via P_i internalization and accumulate high amounts of P_i in the form of polyphosphate (polyP).Hypothesis/Gap Statement. This study investigates whether the carbohydrate metabolism of Rd that generates acid and solubilizes P_i, derived from phosphorus-32 (³²P)-labelled tooth enamel, can be internalized and incorporated into intracellular polyP. The study investigated the hypothesis that the internalization of tooth-derived P_i and polyP synthesis could be attenuated.Aim. A radionuclide ³²P-labelled remineralized model examined the influence of gallein, an inhibitor of polyP kinases, on the ingestion of tooth-derived P_i and on the bacterium's cultivability.Methodology. Radionuclide ³²P-labelled remineralized bovine enamel (n=6) was exposed to Rd (ATCC 17931) incubated in brain heart infusion (BHI) broth containing glucose. Attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy and cross-polarization optical coherence tomography assessed the surface and subsurface characteristics of the remineralized and demineralized enamel surface. Liquid scintillation traced the ³²P release from the tooth to the intracellular polyP in gallein^pos/neg samples. Cell-media, supernatant, cell resuspension, and extracted polyP, from Rd exposed to the radioisotope-labelled remineralized enamel, were analysed for ³²P activity at 10 and 22 h time points.Results. FTIR determined that ³²P was incorporated in dental enamel lesions and was released after exposure to an acidic buffer (pH=4.5) or Rd. After 24 h of exposure, gallein^pos reduced Rd's planktonic growth and increased pH by 7.45% and 7.19%, respectively, compared to gallein^neg. Gallein inhibited the cultivability of planktonic Rd on BHI agar plates with a 13- to 60-fold reduction of c.f.u. ml^-1 (25 µM-13.03×, 50 µM-19.58× and 100 µM-60.57×) compared to gallein^neg samples. Isotope labelling demonstrated that Rd used P_i derived directly from the tooth for the benefit of the bacterium's fitness through the formation of polyP.Conclusion. Rd used the P_i derived directly from the tooth for the benefit of the bacterium's fitness. Gallein attenuated polyP accumulation, reduced bacterial cultivability and may be a potential therapy option in the prevention and treatment of primary and secondary caries.