Effect of ferrioxamine on the growth of Rhizopus

Zygomycosis, caused by Rhizopus spp., has recently been reported to occur in dialysis patients treated with desferrioxamine, suggesting a role of this drug in the pathogenesis of this infection. The hypothesis that ferrioxamine, the iron chelate of desferrioxamine, stimulates the growth of Rhizopus spp. has been brought forward. The growth rate of 2 x 10(5) spores of R. rhizopodiformis (isolated from a dialysis patient who died of zygomycosis while on desferrioxamine therapy) was studied in an iron-deficient medium (1) with human serum at increasing concentrations and (2) with 40% human serum in the presence of ferrioxamine at different concentrations. After grinding the mycelium, growth was measured by absorbance density at 450 nm. The results show that a concentration of 40% human serum inhibits the growth of R. rhizopodiformis > 50% and that, in the presence of serum, ferrioxamine causes a significant growth stimulation at 24 h that persists at 48 h. In conclusion, ferrioxamine stimulates the growth of R. rhizopodiformis in vitro. This probably plays a key role in the pathogenesis of desferrioxamine-related zygomycosis.