Extracellular volume in streptococcal model biofilms: effects of pH, calcium and fluoride.
Diffusion, which limits nutrient penetration and end-product export in biofilms, is restricted by reversible binding and extracellular volume fraction (Ve). Fluoride has been demonstrated to prevent calcium bridging, hence inhibiting calcium-mediated cell association (Rose, Lee and Shellis, Caries Res. 30 (1996) 458-464). 3H-inulin effusion measurements from streptococcal model plaques, at pH 7.0 or 5.0, 0-20 mmol/l Ca2+, and with or without 5 mmol/l KF, demonstrated that Ve was greatest in the absence of added Ca2+ and at pH 7.0, lowest at 20 mmol/l Ca2+ and pH 5.0, and that F- raised the minimum Ve. By bridging adjacent cells and reducing the net negative charge, calcium and low pH, respectively, reduce Ve. Fluoride eliminates the calcium-bridging effect, hence increasing Ve.
Rose
R K
RK
MRC Dental Group, Dental School, Bristol, UK. keith.rose@bristol.ac.uk
Turner
S J
SJ
D001422:Bacterial Adhesion / Q000187:drug effects; D018441:Biofilms / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D003731:Dental Caries / Q000382:microbiology / Q000517:prevention & control; D004058:Diffusion; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D013295:Streptococcus mutans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
D005459:Fluorides; D002118:Calcium