Abstract: OBJECTIVE: Relationships between bacterial concentrations and optical density[D(λ),λ is the wavelength value] in the Salmonella typhimurium reverse mutation assay (Ames test) was investigated and a method for the determination of bacterial concentrations using optical density was developed. METHODS: TA102,a frequently-used auxotrophic Salmonella typhimurium in the Ames test,was selected as the test strain. The amplification conditions of the bacterial solution were strictly controlled. The wavelength of 540 and 600 nm were compared to choose the optimal wavelength for the determination of optical density,and the time of 0,2,4,6,8,10,12 and 14 hours were compared to choose the optimal times for amplification. Under the optimal wavelength and amplification time,the optical density of the bacterial solution was measured,and the bacterial concentration was obtained by plate colony-counting method. Then the regression equation between the bacterial concentration and the optical density was obtained. RESULTS: The optimal wavelength of strain TA102 was 540 nm,and the optimal culture condition was 100 r/min at 37℃ for 10 hours. The linear regression equation between the bacterial concentration and D(540) value was y=4×10⁹x (in the equation,x was D(540) value;y was bacterial concentration with the unit of/mL). CONCLUSION: Through the linear regression equation between the bacterial concentration and D(540) value,real-time control of the bacterial solution to reach the required concentration was achieved by measuring D(540) value,so as to ensure the quality of bacterial solution.

Key words: Ames test, Salmonella typhimurium, bacterial concentration, optical density