Antibacterial action of condensed phosphates on the bacterium Streptococcus mutans and experimental caries in the hamster

Abstract

Condensed phosphates (CP: Na salts of pyro- ∗, tripoly- ∗, tetrapoly- ∗, pentapoly- ∗, hexameta- ∗ and ultra-; K salts of pyro- and poly-) used as food additives depressed the growth of seven strains of Streptococcus mutans (serotype a- g) as assessed by disc diffusion methods. Minimal inhibitory concentrations (MIC) of CP on growth of strain Kl-R ( g) in a chemically defined medium were measured turbidimetrically. Commercial grade CP (∗CP used) had the same growth inhibitory effects as purified linear type CP and they were superior to the cyclic type CP. The MIC of CP for Strep. mutans appeared to be related to their chelating capacity. As the growth inhibition by CP was reversed by the addition of divalent metal ions (Ca 2+, Mg 2+ or Mn 2+), the chelating capacity of CP was apparently responsible for their antibacterial action. The antibacterial action of CP seemed largely bacteriostatic. Condensed phosphates depressed lactate production from glucose and sucrose by the cells of strain Kl-R. A similar inhibition was produced by the supernatant of heated human saliva. Condensed phosphates depressed insoluble glucan production from sucrose by the cells of strain Kl-R. The inhibition of sugar metabolism may be due to the interference of sugar transport into Strep. mutans induced by the chelation effects of CP. Hamsters were inoculated orally with strain Kl-R and reared on the high-sucrose diet No. 2000 supplemented with 2 per cent (w/w) CP for 60 days. Dietary supplements of CP were associated with reduced caries activity ( p < 0.01) and plaque formation ( p < 0.05). The antibacterial actions of CP could be responsible for these caries-inhibitory effects.