Comparative Efficacy of Bactericidal Compounds in Buffer Solutions Part II

Abstract

A number of phenols, aromatic alcohols, organic mercury compounds andquaternary ammoniumcompounds have beenexamined, by the membrane filter method, to assess their antibacterial action at four different pH values against various Gram-positive and Gram-negative organisms. The killing rate of the compounds tested varied with the pH. The phenols, in the undissociated state, and the aromatic alcohols were most effective against Gram-negative cells at a slightly alkaline pH, and least effective at a pH of 5.5 to 7, whereas against Gram-positive cells, the compounds were least bactericidal at a pH of 7 to 8.5 Upon Gram-positive as well as Gram-negative cells, phenylmercuric borate was more potent in alkaline solution, thiomersal, in acid solution. This difference is connected with the opposite charges of the active ions. A reduction in bactericidal activity was noted in acid solutions of domiphen bromide and cetyl pyridinium chloride although the activity of the latter was less influenced by pH. The importance of the partition ratio between water and a lipid phase for the bactericidal efficacy of phenols and aromatic alcohols is stressed, and a new approach to the testing of these compounds is proposed. 4-Chloro- 8- phenylethyl alcohol yielded promising results as a new bactericidal agent. Pseudomonas pyocyanea was more rapidly killed by the compounds tested than Escherichia coli.