Morphological Changes Of Sporothrix Schenckii Treated By Itraconazole And Terbinafine

Background Sporotrichosis caused by Sporothrix schenckii is a kind of deep mycosis, which can cause skin and subcutaneous tissue infections, but visceral organs are rarely involved. Clinically, Sporotrichosis is divided into four types: lymphatic vessel type, fixed type, visceral type and disseminated Sporotrichosis. Lymphatic vessel type is the most common type among them. Saturated potassium iodide is the first line treatment for cutaneous Sporotrichosis, yet the mechanism is unclear so far, and side effects of saturated potassium iodide lead to poor tolerability. Recently, itraconazole (ITZ) and terbinafine (TBF) are found to be effective for treatment of Sporotrichosis in many literature reports. To treat Sportrichosis effectively, it is of great significance to choose effective antifungal drug and study the specific mechanisms of antifungal agents for the effective treatment of Sporotrichosis.In previous years, anti-fungal mechanism of itraconazole and terbinafine were studied. The studies have shown that both of them influenced synthesis of ergosterol which was component of fungal cell membrane, but they interacted with fungus at the different sites. Terbinafine inhibits squalene cyclooxygenase, which then lead to reduction of ergosterol synthesis in cell membrane. Also, squalene accumulation damage cell membrane, which induced cell death. Itraconazole inhibits the c- atalytic activity of cytochrome P450 enzymes by binding to it to inhibit formation of ergosterol. In short, the two drugs induce cell death by inhibiting ergosterol synthesis. However, there was not much study focused on morphological changes of fungi after treatment of anti-fungus drugs.Objective To investigate the anti-Sporothrix schenckii activity of itraconazole and terbinafine and its mechanism, evaluate the effects of itraconazole and terbinafine against Sporothrix schenckii, in vitro drug sensitivity tests of the two antifungal drugs against different Sporothrix schenckii strains(a fixed strain and a lymphatic vessel strain)were performed. To explore the anti-fungi mechanism of itraconazole and terbinafine, morphological changes of Sporothrix schenckii treated by itraconazole and terbinafine were observed with electronic microscope.Methods The anti-Sporothrix schenckii activity of itraconazole and terbinafine was evaluated by microdilution method. The minimum inhibitory concentration (MIC) of itraconazole and terbinafine against three clinically isolated Sporothrix schenckii strains were determined by microdilution method. Ultrastructure of Sporothrix schenckii before and after antifungal drug treatment was observed with electronic microscope. Morphological features of fungal samples before and after treatment were observed under light microscope, scanning electron microscope and transmission electron microscope.Results The fixed strains and lymph-vascular strains were all susceptible to itraconazole and their MIC ranged from 8μg/ml to 16ug/ml. The fixed strains and lymph-vascular strains were all susceptible to terbinafine and their MIC ranged from 4μg/ml to 8ug/ml. Electronic microscopy showed withered hyphae, loosen and deformed surface of conidia wall, shrinking cytoplasm, and obscure cell membrane, cell wall, nuclear and organelle after itraconazole and terbinafine treatment.Conclusion Itraconazole and terbinafine showed excellent anti-Sporothrix schenckii activity against clinically isolated Sporothrix schenckii in vitro, and there were no significant differences between the fixed strain, lymphatic vessel strain and disseminated strain. Electron microscopy results suggest that itraconazole and terbinafine significantly inhibited the growth of Sporothrix schenckii. The two drugs may undermining the membrane selective permeability by destroying the cell wall and membrane of Sporothrix, so that to reduce the intracellular osmotic pressure, a large number of cell contents extravasates, disrupts the normal metabolism, promotes cell death. After the interaction of itraconazole and terbinafine, ultrastructures of Sporothrix schenckii undergo similar changes.