Mechanisms of antifungal activity of copper (CuSO4) on Candida species

Gonçalves Rodrigues, A., C. Pina-Vaz, S. Costa-de-Oliveira, C. Tavares, P. Märdh, J. Martinez-de-Oliveira, A. Freitas da Fonseca (Porto, P; Lund, S)


Mucocutaneous candidosis is the most common clinical manifestation with Candida. The growing emergence of antifungal resistance stresses the need of alternative and/or complementary medications. Objectives: to evaluate the mechanisms of antifungal activity of CuSO4, estimated as the minimal inhibitory concentration (MIC) and minimal lethal concentration (MLC) on the most commonly pathogenic Candida species. Materials and Methods: The fungistatic activity was studied with the fluorescent probe FUN-1 and observation under epifluorescence microscopy and flow cytometry; MIC was also determined according the NCCLS protocol M 27-A. The fungicidal activity was assayed by MLC and viability counts (CFU). Membrane alterations induced in the yeast cells were evaluated by quantification of intracellular K+ leakage and by staining with propidium iodide (PI) followed by flow cytometry. Fourteen clinical isolates of Candida (4 C. albicans, 3 C. parapsilosis, 2 C. krusei, 2 C. glabrata, 2 C. tropicalis, 1 C. guilliermondii) were tested at serial concentrations of CuSO45H2O, ranging from 1 to 10 mM, in RPMI 1640 medium. MIC for fluconazole and amphotericin B were also determined for each strain. Results: MIC was 2.5 mM for all tested strains, except for one strain of C. glabrata that had a MIC of 5mM. MIC corresponded to MLC in seven strains; MLC was 2 times higher the corresponding MIC in the remaining strains. No correlation was found between MIC or MLC and the susceptibility pattern to antifungals. The impairment of metabolic activity resulting from the lowest concentrations could be detected with FUN-1. The CuSO4 concentrations associated to an extensive rate of killing induced permeability to PI and marked efflux of intracellular K+. Conclusions: At lower concentrations copper demonstrated a fungistatic activity, due to yeast metabolic impairment, while at higher concentrations (commonly used in mouth rinses) produced a fungicidal effect, due to direct damage to the cytoplasmic membrane of Candida species, either sensitive or resistant to antifungals. Our results support the use of aqueous copper solutions in the treatment of mucocutaneous candidosis.

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11th European Congress of Clinical Microbiology and Infectious Diseases
    • ECCMID 11th (2001)