Effects of hydrogen peroxide on growth and selected properties of Porphyromonas gingivalis

In this study we first evaluated the effects of hydrogen peroxide (H2O2) on growth and selected properties of Porphyromonas gingivalis, and compared t hem with those obtained by a reducing agent (cysteine). The growth of P. gi ngivalis was only moderately affected when H2O2 was added at concentrations up to 30 mM in a complex culture medium. However, when a defined basal med ium was used, H2O2 at a concentration of 3 mM completely inhibited growth o f P. gingivalis. Incorporation of cysteine at concentrations up to 30 mM in both media had no effect on growth. The effects of H2O2 and cysteine on ce ll-associated hemagglutinating and Arg-gingipain activities were evaluated using bacteria grown in the complex culture medium. Both activities were st rongly decreased when H2O2 was added in the assay mixtures. This inhibitory effect of H2O2 was reversible. On the other hand, including cysteine in th e assay mixtures increased both activities. H2O2 and cysteine had no effect on the expression of heat shock protein (HSP)-68 and HSP-75 by P. gingival is, as determined by SDS-PAGE and Western immunoblotting analysis. In the s econd part of the study, we tested whether growth of selected oral bacteria l species may modify the oxidation-reduction potential (Eh) of the environm ent. II was found that certain species were able to either decrease (P. gin givalis, Fusobacterium nucleatum, Peptostreptococcus micros, Streptococcus mutans) or increase (Streptococcus sanguis) the Eh of the medium. Our study provides evidence that an oxidizing agent such as H2O2 may affect the biol ogy of P. gingivalis. Moreover, growth of some members of the oral microflo ra can generate oxidizing and reducing conditions, and thus potentially inf luence the ecology of subgingival sites by affecting strictly anaerobic bac teria such as P. gingivalis. (C) 1999 Federation of European Microbiologica l Societies. Published by Elsevier Science B.V. All rights reserved.