In Vitro Antifungal Susceptibilities ofSporothrix schenckiiin Two Growth Phases

Abstract

We have determined the antifungal susceptibilities of 34 clinical isolates of the dimorphic fungus Sporothrix schenckii to 11 drugs using a microdilution method. In general, the type of growth phase (mycelial or yeast) and the temperature of incubation (30 or 35°C) exerted a significant influence on the MICs.Sporothrix schenckii is a thermally dimorphic fungus and the most common agent of subcutaneous mycosis in Latin America (2, 12). Pulmonary and disseminated sporotrichosis can also occur when S. schenckii conidia are inhaled (16). Itraconazole (ITC) is generally used for the treatment of lymphocutaneous infection (3, 13, 21), while amphotericin B (AMB) is indicated for severe infections or when ITC therapy fails (9). Although these drugs are generally effective, the long duration of therapy and the strong toxicity of AMB make it necessary to explore new alternatives for the treatment of severe infections.The infective form of sporotrichosis is the yeast phase (Y). However, the reference methods for in vitro antifungal susceptibility testing propose conditions only for the testing of its mycelial phase (M) (19). Testing of Y requires the use of other conditions. Although the optimal temperature for the in vitro growth of S. schenckii ranges from 25°C to 30°C (7), the reference method recommends a temperature of incubation of 35°C. The few studies that have determined the in vitro antifungal susceptibility of S. schenckii have used as the inoculum a mixture of hyphae and conidia obtained from its M (8, 14). We have evaluated the in vitro activities of 11 antifungal agents against clinical isolates of S. schenckii in order to determine if the form of growth and temperature of incubation can influence the MICs.A total of 34 isolates were tested (18 were from patients with disseminated sporotrichosis, 15 were from patients with the lymphocutaneous or cutaneous form of infection, and 1 was from domestic dust). Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 were used as control strains.The following 11 antifungal agents were tested by a microdilution method (18, 19): albaconazole (ABC), AMB, eberconazole (EBC), flucytosine (5FC), fluconazole (FLC), ITC, ketoconazole (KTC), micafungin (MFG), ravuconazole (RVC), terbinafine (TRB), and voriconazole (VRC).To convert S. schenckii into Y, the procedure was performed as described by Ghosh et al. (7). Mycelial cultures grown on potato dextrose agar (PDA) were subcultured on brain heart infusion agar supplemented with 5% defibrinated sheep blood at 37°C for approximately 6 to 9 days. Several successive passages were done to achieve Y. The suspensions were adjusted hemacytometrically, diluted 1:50, and further diluted 1:20 in RPMI to obtain double the final inoculum, which ranged from 1.0 ϫ 10 5 to 5.0 ϫ 10 5 CFU/ml. This inoculum was similar to that used by Nakai et al. schenckii from patients with cutaneous and disseminated sporotrichosis. Geometric means for panel A, disseminated, 2.13 g/ml; cutaneous, 0.63 g/ml (P ϭ 0.035, independent samples t test); geomet...

Sporothrix schenckii and Sporotrichosis

“…Some S. schenckii strains are susceptible to voriconazole in vitro, since MIC values of as low as 0.12 g/ml have been found (107); however, the high geometric mean MIC values, ranging from 6.50 g/ml (155) to 13.2 g/ml (152), suggest that most isolates are resistant in vitro to this drug. High micafungin MIC values have been reported by all but one study (152,172,207,257). However, the interaction of micafungin and itraconazole shows a synergy against S. schenckii (207).…”

“…S. schenckii susceptibility to this triazole drug ranges from 0.03 to more than 16 g/ml. Although some strains can show resistance to this drug, geometric means commonly are low, ranging from 0.4 g/ml (9) to 4.08 g/ml (257). In general, despite the use of fluconazole as a therapeutic agent in some human and veterinary sporotrichosis cases (31,50), this antifungal does not inhibit S. schenckii growth in vitro (9,63,90,152,172,257).…”

“…Although some strains can show resistance to this drug, geometric means commonly are low, ranging from 0.4 g/ml (9) to 4.08 g/ml (257). In general, despite the use of fluconazole as a therapeutic agent in some human and veterinary sporotrichosis cases (31,50), this antifungal does not inhibit S. schenckii growth in vitro (9,63,90,152,172,257). Some S. schenckii strains are susceptible to voriconazole in vitro, since MIC values of as low as 0.12 g/ml have been found (107); however, the high geometric mean MIC values, ranging from 6.50 g/ml (155) to 13.2 g/ml (152), suggest that most isolates are resistant in vitro to this drug.…”

Sporothrix brasiliensis,S. globosa, andS. mexicana, Three NewSporothrixSpecies of Clinical Interest

“…In a recent multilocus study, we investigated the population structure of S. schenckii and showed the existence of at least six putative phylogenetic species prevalent in different geographical regions (20). In several in vitro antifungal susceptibility studies of clinical isolates of S. schenckii, a wide range of susceptibility to different drugs has been demonstrated (16,21,31). This suggests that these isolates could represent different species.…”

Efficacy of terbinafine and itraconazole on a experimental model of systemic sporotrichosis

“…The antifungal activities of these compounds are based on the inhibition of fungal ergosterol biosynthesis at the point of squalene epoxidation, leading to the intracellular accumulation of squalene, which causes the rapid death of fungi. It has demonstrated activity against most superficial fungal infections, including onychomycosis and dermatomycosis, and systemic fungal infections, such as histoplasmosis, Pneumocystis carinii infection, and aspergillosis (3,4,9,17,18,19,20). In this study, our aim was to determine the in vivo efficacy of terbinafine and itraconazole on a experimental model of systemic sporotrichosis.…”