COMBINED INHIBITORY EFFECT OF FLUORIDE AND HYPOTHIOCYANITE ON THE VIABILITY AND GLUCOSE-METABOLISM OF STREPTOCOCCUS-MUTANS, SEROTYPE-C

The separate and combined effects of peroxidase-generated hypothiocyan ite (HOSCN/OSCN-) and F- ions on glucose uptake and growth of Streptoc occus mutans ATCC 25175 were investigated. S. mutans cells were grown to late exponential or stationary growth phase, harvested, washed and suspended in 2.0 mi of sterilized human whole saliva supplemented with 10 mM D-glucose. This saliva-bacteria mixture was supplemented with 5 -150 mu M H2O2 at pH 5.0 or 6.5. At pH 5.0, up to 103+/-21 mu M HOSCN/ OSCN- was generated. After 20 h of incubation at 37 degrees C, the sal iva-bacteria suspension exposed to HOSCN/OSCN- were plated on mitis sa livarius agar plates and incubated anaerobically for 2 days. Identical experiments were made with F- ions (0.5, 1.0 and 5.0 mM). Both HOSCN/ OSCN- and F- caused a significant dose-dependent growth inhibition at pH 5.0, whereas no inhibition was observed at pH 6.5. When F- and HOSC N/OSCN- were added simultaneously at pH 5.0, an additive effect of gro wth inhibition was observed. In glucose incorporation experiments the bacteria-saliva mixture was exposed to 1 mu M HOSCN/OSCN-, 0.5 mM F- o r both. F-, HOSCN/OSCN- or their combination in sterilized whole saliv a at pH 5.0 caused 14.2, 67.8 and 74.2% inhibition, respectively. Thes e observations indicate that F- and HOSCN/OSCN- ions have an additive inhibitory effect on S. mutans and therefore their combination is like ly to be more antibacterial than either agent alone.