The polymyxin sensitivity and the phosphatidyl ethanolamine content of the Vibrio cholerae membranes

The phospholipid composition of three different strains of Vibrio cholerae was determined by quantitative two-dimensional thin-layer chromatography. The polymyxin sensitivity of the whole organisms or of the liposomes derived from the total phospholipids of these organisms depended solely on the phosphatidyl ethanolamine content of the system concerned and could be quantitatively related by the equations Y1 = 1.074 X1 - 9.828 and Y2 = 1.22 X2 - 34.47 where Y represents the maximum lysis (%)/hr and X, the % phosphatidyl ethanolamine content of the system concerned, the suffix 1 and 2 corresponding to the liposomal and the whole organisms respectively. The analysis revealed the requirement of a threshold amount of phosphatidyl ethanolamine for the expression of polymyxin action on the system concerned.