Post-hydrogen Peroxide Effect in Peroxidogenic Oral Streptococci

The effects of inhibitory concentrations of hydrogen peroxide on the growth of 11 strains of four peroxidogenic species of oral streptococci ( Streptococcus oralis, Streptococcus mitis, Streptococcus sanguis and Streptococcus sobrinus ) were studied. The effect of H 2 O 2 was measured as the post-hydrogen peroxide effect (PHPE), defined as the difference in the time necessary for the bacterial population in batch culture to increase by one decimal logarithmic unit ofthe number of colony forming units per millilitre, between cultures cxposed to a concentration equal to the corresponding minimum inhibitory concentration of H 2 O 2 , and non-exposed cultures. No PHPE was shown by S. oralis NCTC 11427; other strains tested gave times ranging from 20 min ( S. sanguis JENA 2697) to 9 h 15 min ( S. mitis OGS 232). The PHPE appears to be strain- and species-dependent' Keywords - Hydrogen peroxide; Oral streptococci; Post-hydrogen peroxide effect.