Antimicrobial actions of hexachlorophene: cytological manifestations

Hexachlorophene is a soap-compatible bisphenol that has been widely used as an antiseptic, yet its mechanism of action is undefined. The relative threshold concentration for bactericidal effect on a susceptible test organism, Bacillus megaterium, was established to be about 10 mug/mg of cell dry weight. At this or at high (>/=100 mug/mg) concentration, adsorptive uptake by cells displayed saturation kinetics. At about 30 mug/mg, the time course of adsorption occurred in three distinct stages. The triphasic pattern was interpreted to represent successive penetration of and adsorption by the cell wall, the protoplast membrane, and the cytoplasm. This interpretation was substantiated by determinations of hexachlorophene adsorption by isolated cell components. Electron microscopy disclosed cytopathology, evidenced as gaps or discontinuities, in the protoplast membrane (but not in the cell wall or cytoplasm) at > 30 mug of hexachlorophene per mg of cell dry weight. Similarly, treatment with > 30 mug/mg allowed a fluorescigenic dye (tolyl-peri acid) to penetrate into the protoplast. However, no detectable cytological manifestations were discerned at the minimum lethal concentration of 10 mug/mg. Apparently, hexachlorophene is physically disruptive at intermediate or high relative concentrations but acts in a more subtle fashion at the minimal lethal concentration.