Choromoblastomycosis (CBM) is a disease caused by traumatic implantation of many species of melanized fungi. The State of Pará is the major endemic area in Brazil and Fonsecaea pedrosoi is the major etiological agent. The treatment is not standardized and many forms of interventions are related in the literature. In the other hand, the in vitro susceptibility test to antifungal drugs may help in the therapeutic choice and in the identification of resistant strains. The objective of this work is to evaluate the in vitro susceptibility of 20 F. pedrosoi clinical isolates to itraconazole (ITZ), ketoconazole (KCZ), fluconazole (FCZ) and terbinafine (TBF) as well as the possible morphological alterations induced by ITZ or TBF in the Minimal Inhibitory Concentration (MIC) and high concentrations. The tests were performed according to the Clinical and Laboratory Standards Institute (CLSI, M38-A2 document) recommendations. The final concentrations of ITZ, TBF and KCZ in each test were to 16 to 0.03 μg/mL. To FCZ the final concentrations were to 64 to 0.125 μg/mL. The MIC was defined as the lowest drug concentration that inhibit 100% the visual growth when compared to the non-treated group after five days of incubation at 30°C. ITZ proved to be the most effective drug in vitro against F. pedrosoi (CIM 90= 1μg/mL). TBF showed a low drug activity with 70% of the isolates with MIC ≥ 0.5 μg/mL. The conidia morphological analysis revealed an increasing in the diameter, an interruption of the cellular division and the formation of little chains after the treatment with ITZ in the MIC. At the high concentration used in the susceptibility test we noticed an irregular shape, a detachment of pigmented material from the cell wall and a vacuolization. Rupture in cell wall and amorphous conidia were observed at 32 μg/mL and 64 μg/mL. Significant alterations were not observed after treatment with TBF at the same concentrations. Moreover, the 5-fluorocytocise (5-FC) and FCZ do not stop the conidia growth at high concentrations. However, ultrastructure alterations were noticed after treatment with 5-FC 64 μg/mL. Thus, it is suggested a different morphological pattern after ITZ or TBF treatment during the in vitro susceptibility test. In synthesis, ITZ shown better in vitro antifungal activity while 5-FC only provoked structures alterations in the highest concentration tested.
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