Antifungal action of Hevea brasiliensis latex. Its effect in combination with fluconazole on Candida albicans growth.

Abstract

Latex from Hevea brasiliensis and its subcellular fractions (L-serum and C-serum) were tested for antifungal activity alone or in combination with fluconazole. Candida albicans growth was inhibited with the same efficacy when yeasts were inoculated into culture medium supplemented over the total growth phase with latex as when latex was added during the exponential phase only: the minimum inhibitory concentration (MIC 80%) of H. brasiliensis latex was 123 micrograms protein ml-1. By means of a non-linear regression analysis of the experimental data, two distinct fixation sites for fluconazole (FCZ) could be determined: one of strong affinity (Kaff = 0.0162 microgram-1 protein ml) and another of low affinity (Kaff = 0.0071 microgram-1 protein ml). After addition of a mixture of FCZ and latex during the exponential phase, the affinity constant of yeasts for FCZ was calculated: when latex was in a final concentration of 21 micrograms protein ml-1 (Kaff = 1 microgram-1 protein ml) or 42 micrograms protein ml-1 (Kaff = 0.277 microgram-1 protein ml) and without latex (Kaff = 0.0502 microgram-1 protein ml). In two cases a synergistic effect between latex and FCZ was obtained. The highest efficacy was obtained with a latex concentration of 21 micrograms protein ml-1. The addition of subcellular fractions of latex, L-serum and C-serum, did not cause an antifungal effect. The indispensable role of rubber particles for raising an antifungal effect is demonstrated. Electron microscopy observations indicated a limited cell wall degradation and a high percentage of coagulated yeasts.