Membrane Disorders of Escherichia coli Cells and Liposomes Induced by p-Hydroxybenzoic Acid Esters: The Antimicrobial Action of p-Hydroxybenzoic Acid Esters. V

p-Hydroxybenzoic acid esters (parabens) inhibited the uptakes of not only proline but also glucose and acetate into cells of Escherichia coli JE1011 in the presence of chloramphenicol. The inhibition was enhanced at higher temperatures, and by longer alkyl side chains of parabens. Parabens injured artificial phospholipid membrane vesicles (liposomes) formed from phosphatidylcholine, cholesterol and stearylamine (molar ratio, 7:1:2), as revealed by the leakage of glucose from the liposomes, and the liposomes were disintegrated by butylparaben at high concentration. The 31P nuclear magnetic resonance (31P NMR) spectra of phosphatidylcholine showed a sharp peak corresponding to orthophosphoric acid in the presence of butylparaben. It was recognized from the change of the 31P NMR spectral pattern that butylparaben made the phase transition temperature of phosphatidylethanolamine 15° lower. The molar ratios of parabens to phospholipids in the three experiments, the uptake experiment using Escherichia coli cells, the leakage experiment using liposomes and the 31P NMR experiment, were roughly estimated at 0.08-0.5:1, 0.5-1.5:1 and 0.12-0.28:1, respectively. These results indicated that parabens disordered the membrane lipid, and nonspecifically inhibited the functions, such as uptake of substances, of the cell membrane. The membranes began to disintegrate at higher concentrations of parabens.