Action of Biguanides, Phenols and Detergents on Escherichia coli and its Spheroplasts

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Abstract
Summary: The bactericidal potency of groups of biguanides, phenols and detergents has been compared with that of the bis‐biguanide, chlorhexidine, and related to measurable effects of the compounds on bacteria. Biguanides, like chlorhexidine, precipitated bacterial cytoplasm and also lysed spheroplasts over a limited concentration range: higher concentrations prevented lysis. Certain phenols and detergents which lysed spheroplasts did not precipitate cytoplasm. All the compounds released radioactivity from isotopically labelled bacteria; at suitable concentrations, biguanides released more radioactivity than chlorhexidine, but at higher concentrations the amount of radioactivity released was reduced. Bactericidal activity correlated with both the ability to lyse spheroplasts and to precipitate cytoplasm from solution. The findings support the hypothesis that damage to the cell wall alone does not kill bacteria but an increase in permeability allows entry of the bactericide. Action of compounds on the cell wall is discussed in relation to a model of its ultrastructure.