L-DOPA accessibility in culture medium increases melanin expression and virulence ofSporothrix schenckiiyeast cells

Abstract

Melanin is a complex polymer widely distributed in nature and has been described as an important virulence factor in several pathogenic fungi, including Sporothrix schenckii. The aim of the present work was to investigate the presence of melanin on the surface of S. schenckii yeast cells which showed differences in their virulence depending on the culture conditions under which they were grown. Yeast cells were cultivated in brain heart infusion (BHI) broth from Difco and Oxoid. BHI from these two vendors are different in their brain and heart infusion contents. Yeasts cultivated in the medium containing the higher brain infusion content were highly virulent as ascertained by the mice mortality rate, CFU and histopathology. Transmission electron microscopy revealed a higher expression of electron dense granules on the fungal cell wall of the most virulent yeast cells. Flow cytometry analysis, with anti-melanin antibodies, confirmed that this pigment was melanin. Furthermore, spectrophotometric analysis showed a higher concentration of this polymer on NaOH and cell wall extracts of the most virulent yeast cells. These results suggest that differences in the relative content of brain and heart infusion in the culture medium modulated melanin expression on the surface of S. schenckii yeast cells and, as a consequence, virulence. A new pathway of melanin biosynthesis in S. schenckii is proposed which involves the use of phenolic compounds from rich brain medium as melanin substrate.

Miltefosine is active against Sporothrix brasiliensis isolates with in vitro low susceptibility to amphotericin B or itraconazole

“…This electrondense material visualized by TEM is morphologically similar to the melanin granules described by Teixeira et al (2010). In addition, flow cytometry analysis using antimelanin antibodies showed that miltefosine-treated cells had increased melanin content compared to untreated cells.…”

“…3b). Teixeira et al (2010) have described similar electron-dense material inside the cell wall as melanin deposits. Treatment with 0.5 mg ml 21 of miltefosine induced changes in the ultrastructure of S. brasiliensis yeast cells, such as: decrease in cytoplasmic electron density (Fig.…”

“…Thus, our results suggest that miltefosine treatment could modulate melanin turnover (breakdown and/or production) in S. brasiliensis yeast cells, leading to the accumulation of aggregates of this pigment in the cell wall. Similarly, Teixeira et al (2010) also showed that the amount of melanin in the cell wall of S. schenckii could be modulated by varying culture medium composition (Teixeira et al, 2010).…”

In vitro reduction of pathogenic sporothrix schenckii fungus by photodynamic therapy

“…Thus, the limited effect of the therapy imposed on these groups is observed, since the growth of the microorganism was observed. What can be expected is that the isolate used, even if it consists of a wild culture with all its mechanisms of defense and exchange of genetic material, can present a greater sensitivity to the therapy since there are different types of Sporothrix schenckii cataloged, with several genotypes 10,11 . Thus, this study indicated the efficiency of methylene blue as a photosensitizer associated with a low power laser in inhibiting the growth of Sporothrix schenckii complex fungi.…”

“…However, due to the indiscriminate use of these drugs, drug-resistant isolates can be identified, which consequently leads to therapeutic failures and remission of mycosis in humans [6][7][8][9] . The diagnosis consists of the microscopic identification of yeast structures of the Sporothrix schenckii complex fungi by the material collected from the lesions 10,11 . Cutaneous sporotrichosis affects people of any age, both sexes, and in various locations favorable to the fungus.…”