Comparison of the Action of Vantocil, Cetrimide and Chlorhexidine on Escherichia coli and its Spheroplasts and the Protoplasts of Gram Positive Bacteria

SUMMARY The actions of chlorhexidine, cetrimide and Vantocil (the hydrochloride of a polymeric biguanide) on bacteria and spheroplasts or protoplasts derived therefrom have been compared. Lysis of Escherichia coli spheroplasts by chlorhexidine or cetrimide is due to rupture of the cytoplasmic membrane. Membranes ruptured with cetrimide can reform to give small, empty envelopes. With increasing concentrations of cetrimide or chlorhexidine more and more granules appear in the cytoplasm, increasing in size with increasing concentration, until the structure becomes transformed to a granular body similar in size to the original spheroplast. With chlorhexidine or Vantocil this now electron‐dense body is rigid, but with cetrimide it collapses to a flat disc which does not lyse. The granules appear to consist of coagulated cytoplasm. This effect of excess of these antiseptics not only prevents osmotic lysis of the spheroplast or the collapsed disc but renders them immune to lysis by a variety of chemical agents. In isolated cytoplasm, chlorhexidine or cetrimide causes precipitation over a narrow range of concentrations but greater than those required for lysis. With Vantocil precipitation occurs gradually over a wide range of concentrations, starting at concentrations equal to those which cause a limited amount of lysis of the spheroplast or a relatively small increase in permeability of intact bacteria. Lanthanous and uranyl ions also precipitate cell contents but do not lyse spheroplasts; spheroplasts treated with these ions are protected from lysis by other agents.