Electrokinetic Studies of Bacteria II: Effect of Cetyltrimethylammoniurn Bromide on Streptococcus faecalis

Abstract

Bacteria were treated with different concentrations of cetyltrimethylammonium bromide in solutions of constant ionic strength equal to 0.01 M, buffered at pH values of 3.4 and 7.0. The initial negative ζ-potential of the bacterial cell wall decreased in absolute value as the concentration of cetyltrimethylammonium bromide was increased, reached zero in the vicinity of the CMC, and then became increasingly positive. This is interpreted as chemisorption of the surface-active cation by ion exchange to form cetyltrimethylammonium carboxylate, followed by physical adsorption of the entire cetyltrimethylammonium bromide molecule. Lysis of the bacteria in the presence of relatively high concentrations of cetyltrimethylammonium bromide increased the positive value of the ζ-potential of the cell wall. Cetyltrimethylammonium bromide completely inhibited the growth of Streptococcus faecalis at a concentration which produced only a 10–30% decrease in the absolute value of the ζ-potential. This seems to indicate that the primary site of attack of the compound is probably not the cell wall.