Inhibitory Effects of Aqueous Onion and Garlic Extracts on Growth and Keratinase Activity in Trichophyton mentagrophytes

The effect of onion and garlic extracts on fungal growth and keratinolytic activity was studied in Trichophyton mentagrophytes as one of the major etiologic agents of human and animal dermatophytosis in Iran and other parts of the world. In order to find out the best keratinase producer for further steps, culture conditions for 30 strains of T. mentagrophytes isolated from human dermatophytosis were optimized on specific solid and liquid media. All of the isolates produced the enzyme on both selective culture media. The maximum keratinolytic activity at submerged cultivation was reported for cultures of T. mentagrophytes isolate No. 1 grown for a 12-day period at 32ºC. Extracellular keratinase activity was in the range of 0.28 to 2.18 u/mg protein in different isolates at predetermined optimal conditions. The growth of T. mentagrophytes isolate No. 1 was inhibited in the presence of various concentrations of onion and garlic extracts. This inhibition reached to a maximum of 100% for both extracts at 10% v/v concentrations. Keratinase synthesis was also inhibited by two extracts as a dose-dependent manner with maximums about 58.54 and 71.36 percent at 5% concentrations, accordingly. In contrast to the fungal growth, keratinolytic activity was inhibited more by garlic as compared with onion extract. This is the first report on keratinase inhibition by these two natural compounds. Since fungal growth and keratinolytic activity are important factors in pathogenesis of the dermatophytes, their inhibition by onion and garlic indicate that these substances may have potential values for treatment of human and animal dermatophytosis