Ozone as disinfectent: effectiveness on cariogenic microbs suspended in PBS

Objectives: To evaluate the potential of ozone on inactivation of cariogenic bacteria suspended in phosphate buffered saline (PBS). Methods: The antibacterial efficacy of ozone was tested against oral streptococci (S. Sobrinus 6715, S. mutans MT8148 and S. gordonii). All these bacteria were freshly cultured and resuspended in sterile PBS. The suspensions were diluted down to OD₅₀₀=2 (approximately 2x10⁷CFU/ml) and preserved separately. Another fresh suspension was prepared by mixing above three bacterial suspensions. Gaseous ozone (HealOzone, KAVO, Germany) was applied by using a blue micro-pipette tip into a 20ml conical flask sealed with rubber cap for 30, 60, 90, 120 and 240s, to the bacterial suspensions separately. The turbidity of individual bacterial cell suspension and mixed suspension after ozone application was measured by using Biotrak II Plate reader (Biochrom Ltd., Cambridge, England). All experiments were repeated three times with triplicate reading. Results: Application of HealOzone dose dependently reduced the turbidity of both mixed and individual bacteria from 30s exposure time. However, there were no significant difference between "Control (no ozone)" and exposure time up to 60s. There were significant (p<0.05) reductions of turbidity in S. gordonii suspension and mixed suspension when exposure time was more than 120s. Conclusion: Ozone had an antibacterial effect on cariogenic bacteria suspended in PBS, even after there is a possibility of reduction of free O₃ radical anion resulting in less powerful oxidant. This study was supported by COE program for FRMDRTB at TMDU and Japan Monbukagaku Research Grant (16390544).