Objectives: S. oralis (formerly S. sanguis serotypeII) have been considered as important beneficial bacteria for periodontal health. Hydrogen peroxide synthesized by S.oralis play a prominent role in prevention of periodontal diseases. The purpose of present study was to investigate the influence of a broad range of environmental conditions on initial rates of hydrogen peroxide produced by S. oralis. Methods: Grown at mid-logarithmic phase, S. oralis were centrifuged and respectively washed by phosphate buffer containing 0.01~100mM glucose and sucrose, Bis-Tris buffer with 5.0~7.5pH and Bis-Tris buffer containing 0.01~100mM Ca2+, 0.01~100mM F- and 0.01~100mM HFPO3-, After S.oralis were cultured in respective buffer for different time at 37°C, the concentration of hydrogen peroxide in supernatant was assayed spectrophotometrically by ABTS-HRP at A405. Results: Synthesis rate of hydrogen peroxide by S.oralis was 7.48nmolH2O2/(min 10xE9 cells) without carbohydrate, the synthesis rate of hydrogen peroxide by S. oralis were increased with 0.01~100nmM glucose and 0.01~100mM sucrose (p<0.05), but there is no statistically significant difference among the each carbohydrate groups except 100mM sucrose. The rates of H2O2 synthesis were inhibited in the buffer at pH5.0~6.0, compared with pH7.0 (p<0.05). Ca2+ has little influences on the rates of H2O2 synthesis. IC50 of H2O2 synthesis rates by S.oralis responded to FHPO3- and F- were 12.65mM and 1.90mM respect. Conclusion: The results indicate that controlling environmental factors may influence the synthesis rate of hydrogen peroxide by S. oralis and the efficiency of inhibiting putative periodontal pathogens. Supported by National Nature Science Foundation of China, grant 39970793.

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