Inhibition of bacterial multiplication by the iron chelator deferoxamine: potentiating effect of ascorbic acid

Since iron is essential for the multiplication of microorganisms, the effect of the iron chelator deferoxamine, with or without ascorbic acid, on the growth of 43 strains of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Alcaligenes faecalis, Neisseria meningitidis and species of Salmonella, Enterobacter, Pseudomonas and Providencia, was investigated with the use of an automated turbidimeter. Addition of deferoxamine (25-400 micrograms/ml) to the incubation medium was inhibitory in a dose-dependent fashion. At concentrations between 200-400 micrograms/ml, growth was about 25% lower than control values. However, when ascorbic acid (100 micrograms/ml) was added to the culture medium, this antimicrobial activity of deferoxamine was significantly increased to on average 75% of the control value (p less than 0.05). Ascorbic acid alone had no bacteriostatic properties. Growth in the presence of 200 micrograms/ml deferoxamine combined with 100 micrograms/ml ascorbic acid was significantly lower than that in control media without additions (p less than 0.001). Addition of ferric citrate to the culture medium at a concentration sufficient to saturate all of the deferoxamine with iron, abolished the growth inhibiting effect of deferoxamine. The results provide evidence that deferoxamine is bacteriostatic due to its capacity to deplete iron which would otherwise be used for bacterial multiplication, and that ascorbic acid enhances this antibacterial property of deferoxamine.