Relationship Between Bactericidal Activity and the Hydrophobicity-Hydrophilicity Balance of Alcohol Solutions

Alcohols showed bactericidal activity against Staphylococcus aureus, Micrococcus luteus, Escherichia coli, and Enterobacter cloacae suspended in 0.85% (v/v) saline in the order of n-butanol>n-propanol>ethanol>methanol.Against the bacteria suspended in n-octane, however, alcohols showed a reverse order of bactericidal effectiveness. When toluene as a hydrophobic solvent was mixed with a small amount of hydrophilic methanol (5 or 10%, v/v), or conversely, when hydrophilic methanol was mixed with a small amount of hydrophobic nhexane (10 or 30%, v/v), the bactericidal activity of the mixture increased markedly. The pattern of the relative glucose-Sudan III solubility curve was similar to that of the bactericidal activity curve of ethanol solutions. The results obtained suggest that the bactericidal activity of an alcohol was not dependent on the logarithm of the partition coefficient of the alcohol but on the hydrophobicity-hydrophilicity balance of the solution.