Bactericidal Action of Ascorbic Acid on Pseudomonas aeruginosa: Alteration of Cell Surface as a Possible Mechanism

Abstract

Neutralized ascorbic acid exerts a strong bactericidal action on P. aeruginosa suspended in isotonic phosphate buffer at pH 7.1. The bactericidal and bacteriostatic action of ascorbic acid are antagonized by Mg ions. In the absence of complex formation between Mg and ascorbic acid it is concluded that ascorbic acid acts by competing with the Mg binding sites in the cell wall, cell membrane or ribosomes. Using the chequer-board titration method the synergistic action of ascorbic acid and erythromycin is determined; such a potentiation of erythromycin is also adversely affected by Mg ions. P. aeruginosa cells, washed and suspended in isotonic phosphate buffer containing ascorbic acid, became increasingly susceptible to the action of polymy xin, erythromycin, chloramphenicol, neomycin and tetracycline. It is suggested that ascorbic acid alters the cell surface to render it increasingly permeable to these antibiotics.