Avaliação do fenômeno de tolerância ao itraconazol em Cryptococcus neoformans

• Ano de defesa: 2022
• Autor(a) principal: Júlio Roger Evangelista dos Santos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; Brasil; ICB - INSTITUTO DE CIÊNCIAS BIOLOGICAS; Programa de Pós-Graduação em Microbiologia; UFMG
• Palavras-chave em Português: Cryptococcus nerformans; Cryptococcus gattii; itraconazol; tolerância; Microbiologia; Cryptococcus neoformans; Itraconazol; Tolerância a medicamentos
• Link de acesso: http://hdl.handle.net/1843/50885

Cryptococcus are encapsulated yeasts that cause cryptococcosis. The main species of clinical importance are Cryptococcus neoformans and C. gattii. The drugs used for its treatment in Brazil are amphotericin B and azole derivatives such as itraconazole. Treatment is long and often ineffective due to fungal adaptation mechanisms, like tolerance. Tolerance is defined as the ability of the fungus to survive in the presence of the drug, even with no change in the minimum inhibitory concentration (MIC). In this context, this study aimed to evaluate the tolerance to itraconazole in different strains of C. neoformans and C. gattii. Initially, the MIC of itraconazole was evaluated for 53 strains of C. neoformans, being 17 wild-type strains and 36 strains with deleted genes, and 16 wild-type strains of C. gattii at temperatures of 30 ºC and 35 ºC. The MIC varied between 0.03 and 2.00 μg/mL, showing a pattern of more susceptible strains at 35 °C for both C. neoformans and C. gattii Subsequently, we selected 17 lines with the highest and lowest MIC values for growth curve analysis at MIC, 2xCIM and 0.5CIM concentrations in order to assess tolerance profile. Next we investigated 10 of these strains, that showed growth in the MIC for the analysis of Colony Forming Units to verify the viability of the cells. We found 4 strains capable of growing at their respective MIC, in which 2 were able to grow at MIC of 30 °C and 35 °C. Tolerance to itraconazole caused a change in the morphology of these cells, which presented an agglomeration of cells and an irregular appearance when compared to untreated strains. The strains tolerant to itraconazole, which is an oxidative stress-inducing agent, did not show an increase in the production of reactive oxygen species and there was no change in the production of ergosterol, which is one of the targets of this drug. These results show us that the response to oxidative stress and the regulation of ergosterol may be some of the possible means of adaptation that contributed to the phenomenon of tolerance.