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 ( ³² P)-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 ³² P-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 ³² P-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 ³² P 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 ³² P activity at 10 and 22 h time points.

Results. FTIR determined that ³² P 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.