The effect of quaternary ammonium derivatives of bile acids on the rate of swelling of Pseudomonas aeruginosa in solutions of sodium and potassium salts

Abstract

Quaternary ammonium derivatives of bile acids increase the rate of swelling of washed cells of Pseudomonas aeruginosa incubated in solutions of potassium phosphate and to a lesser extent in solutions of sodium phosphate. The enhanced swelling is proportional to the concentration of the compounds in potassium but not in sodium solutions. The reason for this is that sodium but not potassium can displace the compounds from their attachment to the cell site(s) and the interaction is mixed competitive noncompetitive. Both cations, however, when added to cells before the compounds inhibit their effect. Formaldehyde-treated cells behave essentially in the same way as normal cells, which indicates that the compounds are not inhibiting metabolic pumps but are facilitating diffusion of the ions. As the steroid portion of the molecule becomes less lipophilic by the introduction of hydroxyl groups their activity decreases.