Inhibition of catalase activity ofCandida albicansby serum

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Abstract
The phenomenon of iron-reversible inhibition of growth of C. albicans in serum, germ-tube formation in serum, and the lack of catalase activity in cells of C. albicans grown in serum-containing media are related events which may demonstrate how initiation of widespread candidiasis is prevented in a “normal” individual. C. albicans depended on iron, added as FeCl3, for growth in neopeptone-glucose broth containing 2–25% pooled human serum. Where serum was omitted, iron additions had a negligible effect on growth. In the presence of serum, C. albicans tends to grow in the mycelial form. The germ-tubes that rapidly grow out from the yeast form are the initiation of mycelia. Addition of 0·2–0·3% phenethyl alcohol to serum resulted in the suppression of germ-tube formation, and the subsequent development of budding yeast cells. The response of C. albicans to FeCl3 in serum-containing media indicates that the mycelial form may have a metabolism requiring iron for continued growth. Since germ-tube formation also occurs in vivo, such a metabolic change in C. albicans in an iron-deficient environment may constitute part of the normal defence of the host against this organism. C. albicans harvested from broth, or from broth containing 25% serum and 20μM FeCl3, had a considerable catalase activity, in contrast to cells from broth containing 25% serum. This was probably due to a lack of iron. A deficiency of catalase would make C. albicans vulnerable to rapid killing by the H2O2-generating system of phagocytes.