Antibacterial effects associated with changes in bacterial cytology produced by cationic polypeptides.

The antibacterial action of cationic polypeptides has been found to be correlated with changes which they produce in the cytochemical reactions of the bacterial cells. Bacterial cells ordinarily stain with cationic dyes at pH values above 7. Treatment with cationic polypeptides rendered them stainable with the anionic dye fast green at pH 8.1. This change occurred parallel to loss of bacterial viability. An anionic, biological substance, mucin, was found to inhibit the usual conversion of bacterial cells from strong basophilia to strong acidophilia in the presence of cationic polypeptide. This inhibitory action was paralleled by inhibition of the toxicity of the cationic polypeptides for the bacterial cells. It was found that the basic protein, globin, which has a lesser pK than total calf thymus histone, was less toxic for E. coli and less effective in causing the bacterial cells to become stainable with the anionic dye at high pH. Staining with fast green at pH 8.1 appeared to provide presumptive evidence of lethal interaction between certain bacterial cells and cationic polypeptides such as total histones. It is suggested that the method may prove to be useful in the detection of lethal interaction between cationic polypeptides of the host and bacteria residing in host tissues.