Mutual Antagonism Between Pathogenic Fungi. Inhibition of Dimorphism in Candida Albicans

SUMMARY

By means of two-membered pure cultures the pathogenic fungi, Trichophyton rubrum and Candida albicans, have been shown to exert antagonistic effects on one another in vitro. The effects observed were (1) inhibition of growth (marked inhibition of T. rubrum by a heat-labile metabolic product of Candida), (2) the production of a yellow-brown color by T. rubrum in the two-membered cultures as a result of acid production by Candida (the pigment of T. rubrum is a pH indicator), (3) complete inhibition of mycelial production by C. albicans.

The latter phenomenon was studied in some detail. Two metabolic products of T. rubrum were shown to inhibit the yeast to mycelial conversion (designated as Y→M). These products were: (1) soluble in water and in acetone, heat stable, adsorbed by Norite and eluted from it by dilute aqueous acid alcohol, (2) soluble in water, insoluble in acetone, heat labile, not adsorbed by Norite.

Conversion of Y→M was independent of pH (4.5-8.0), but was inhibited regularly by high concentrations of NH⁴Cl (3 per cent). It was concluded the active fractions of T. rubrum filtrates were not the H⁺ or NH₄⁺ ions.

The general phenomenon of inhibition of cell division without simultaneous inhibition of growth (resulting in the production of elongated cells) is discussed in some detail. The possibility of inhibition or inactivation of a single enzyme complex responsible for cell division is briefly considered.