Avaliação da produção de melanina em Cryptococcus neoformans sob diferentes condições de cultivo e por meio da eletroforese não-desnaturante: influência in vitro na atividade de antifúngicos

Abstract

Cryptococcosis is an opportunistic fungal infection caused by Cryptococcus neoformans that has presented increased incidence with the great number of immunocompromised patients, mainly AIDS ones, being 474.273, the number of cases registered in Brazil since 1980 to june 2007. Additional studies about microorganism’s pathogenesis is necessary for better comprehension about the aethyological agent, criptococosis and associated factors to virulence. Among virulence’s factors, melanin is one of the mainly and its synthesis occurs by laccases action. So, some studies were performed to evaluate the melanin pigment’s production between clinical and environmental strains of C. neoformans under different conditions of pH (5, 6 and 7) and temperatures (25 °C, 30 °C and 35 °C). The pigment and susceptibility to fluconazole and amphotericin B relation’s was also evaluated. The results showed that there wasn’t comparable behaviour of melanization among the strains. The higher alterations on yeast’s pigmentation and growth were noted under pH 7 and at 35 °C. The electrophoresis technique on non-denaturant PAGE gel showed to be an useful tool to the analysis of laccase produced by C. neoformans strains and posterior quantification of melanin by spot’s densitometry after reaction with L-dopa substrate. The environmental strains showed the higher values of melanin intensities and large variation range. Over than a half of clinical strains (56.2 %) showed the lower melanin’s intensities. The clinical strain, ICB 88 revealed two melanin spots on gel indicating the presence of two laccase isoforms. The susceptibility antifungal tests with fluconazole and amphotericin B through disk diffusion and E-test® methods showed that reading after 72 hours can induce to mistakes on the susceptibility profile of strains, either in presence or absence of melanin. Addition of melanin on medium surface appears not change the results of susceptibility to fluconazole in disk diffusion and E-test®, but to amphotericin B was observed increase of MICs to 90.9 % of strains, been 45.4 % upper to 2 dilutions after addition of melanin in Etest ® methodology.