Effects of common solvent concentrations on bacterial activities

Abstract:

[Objective] To investigate the effects of common organic solvents of dimethyl sulfoxide (DMSO), acetone and ethanol on the activities of bacteria for guiding the selection of solvent and addition of its dosage in the antibacterial test in vitro. [Methods] Consulting the results of growth curve method, conventional antibacterial tests (disk diffusion method and broth dilution method) were used to determine inhibitory effects of DMSO, acetone and ethanol on the bacterial strains of Escherichia coli and Staphylococcus aureus. The changes of cell morphology after treated by these solvents were studied by scanning electron microscope (SEM). [Results] When the solvent inhibitory effects on E. coli and S. aureus were 20%, the concentration (V/V) of solvent DMSO, acetone, ethanol were 1.00%, 0.25%, 2.00% and 1.00%, 1.00%, 0.50% in the broth dilution method, respectively. For the growth curve method, the concentration (V/V) of DMSO, acetone, ethanol were 0.50%, 1.00%, 0.50% and 1.00%, 0.50%, 0.50% when 20% inhibitory effects on E. coli and S. aureus were reached, respectively. 32% (V/V) DMSO and 32% (V/V) ethanol showed obvious inhibitory rings for E. coli, but no inhibitory rings appeared for S. aureus in the same concentrations of studied solvents with disk diffusion method. To compare three methods, the inhibitory effects of DMSO, acetone and ethanol were 20% while their concentrations (V/V) all were lower than 0.5%; under this condition, effects on the viability of bacteria were slight. SEM showed that limited solvent concentrations could decrease their effects on the growth of E. coli. [Conclusion] To compare with DMSO and acetone, ethanol showed a stronger effect on growth and reproduction of microorganisms. After treated with the same concentration of medicinal solvent, liquid testing condition, such as broth dilution method and growth curve method, induced the stronger effect on the cells.