| Abstrakt: |
Melanin synthesis in Cryptococcus neoformans, catalyzed by phenoloxidase activity, is one of the oldest virulence factors known. However, until now, the relationship between melanin production in C. neoformansand its virulence has been poorly understood. Among different chemical compounds only Fe3+and Cu2+cations enhance the phenoloxidase activity in C. neoformans. A few reports in the literature describe the influence of different cations on C. neoformansphenoloxidase activity, excluding iron [1–3]. In this study, 13 C. neoformansstrains isolated from AIDS patients and 7 from bird droppings (B.D.), were examined in order to clarify the effect of different K+concentrations on phenoloxidase activity. A new solid and liquid caffeic acid minimal synthetic medium (MSM-CAF) containing only caffeic acid and ferric citrate with different potassium concentrations was used to evaluate C. neoformansphenoloxidase activity. In the MSM-CAF solid medium the degree of brown pigmentation on the agar plates was read on days 1, 2 and 3 of incubation, and the pigmentation of the C. neoformansstrains was classed into 5 categories. The brown pigment of the liquid MSM-CAF test tubes were checked after 24 hours of incubation by measuring the optical density (O.D.) at 480 nm. Three C. neoformansAIDS and B.D. strains, randomlychosen, were tested for phenoloxidase activity, according to the modified protocols of Polachecket al., Torres-Guerrero et al. and Rhodes [2–4]. According to the results obtained, it has been observed that K+does not activate the phenoloxidase activity in the C. neoformansAIDS and B.D. strains. In particular, with an increase in potassium concentrations in the MSM-CAF solid and liquid medium, there was a corresponding inhibition of the phenoloxidase activity on both the C. neoformansAIDS and B.D. strains. |
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