Abstract
Trichophyton mentagrophytes, a zoophilic species, is one of the most frequently isolated dermatophytes in many parts of the world. This study investigated the efficacy of a sophorolipid (SL-YS3) produced by Rhodotorula babjevae YS3 against dermatophytosis caused by T. mentagrophytes. SL-YS3 was characterized by gas chromatography–mass spectrometry (GC–MS) and ultra-performance liquid chromatography, coupled with electrospray mass spectrometry (UPLC-ESI-MS). SL-YS3 comprised of six different fatty acids as the hydrophobic components of constituent congeners and sophorose as the hydrophilic component. Inhibitory effects of purified SL-YS3 against hyphal growth was found to be 85% at a 2 mg ml–1 concentration, and MIC was 1 mg ml–1. Microscopic examination with scanning electron microscopy (SEM), atomic force microscopy, and confocal laser scanning microscopy (CLSM) revealed that SL-YS3 exerts its effect by disrupting cell membrane integrity causing cell death. SL-YS3 was also effective in reducing the biofilms formed by T. mentagrophytes, which was observed spectrophotometrically with crystal-violet staining and further validated with SEM and CLSM studies of treated biofilms. In vivo studies in a mouse model of cutaneous dermatophytosis involving macroscopic observations, percent culture recovery from skin samples, and histopathological studies showed that SL-YS3 could effectively cure the infected mice after 21 days of topical treatment. Terbinafine (TRB) was used as a standard drug in the experiments. We demonstrate, for the first time, the antidermatophytic activity of a sophorolipid biosurfactant. The findings are suggestive that SL-YS3 can be formulated as a novel antifungal compound to treat cutaneous mycoses caused by T. mentagrophytes.
Highlights
Trichophyton mentagrophytes is a zoonotic dermatophyte found in a variety of environments and is especially dominant in clinical cases of tinea pedis and onychomycosis, with a prevalence of 1.5– 55.4% (Ameen, 2010; Agarwal et al, 2014)
For confocal laser scanning microscopy (CLSM), the treated mycelia were excised and stained with 0.1 mg ml−1 propidium iodide (PI; Sigma-Aldrich) for 15 min, washed in phosphatebuffered saline (PBS), and visualized in a confocal microscope (Leica TCS SP8 with VIS Laser Leica Microsystems, Germany) (Sen et al, 2019)
For CLSM, fungal biofilms post-treatment were gently washed with PBS, stained with 100 μg ml−1 propidium iodide (PI; Sigma-Aldrich, United States), for 15 min and viewed in a confocal microscope (Leica TCS SP8 with VIS Laser Leica microsystems, Germany)
Summary
Trichophyton mentagrophytes is a zoonotic dermatophyte found in a variety of environments and is especially dominant in clinical cases of tinea pedis and onychomycosis, with a prevalence of 1.5– 55.4% (Ameen, 2010; Agarwal et al, 2014). SLs have been reported to stimulate the dermal fibroblast metabolism and collagen neosynthesis, inhibit free radical and elastase activity, possess macrophageactivating and fibrinolytic properties and act as desquamating agents making them attractive candidates for dermatological applications (Van Bogaert et al, 2007). Their compatibility with skin tissue and their tissue healing properties make them attractive candidates for dermal applications (Lydon et al, 2017). The current study was, performed to evaluate the in vitro and in vivo antimycotic activity of an SL biosurfactant extracted from the Rhodotorula babjevae strain YS3, against T. mentagrophytes, as a non-toxic alternative to conventional synthetic antifungals. To the best of our knowledge, this is the first report documenting the antifungal activity of SLs against dermatophytes
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