Exploring hidden dimensions of soil fungal biodiversity: A simple technique to detect soil fungi resistant to antifungal compounds

Abstract

Soils are known to be ultimate and complex reservoirs of microbial diversity. The complex dimensions of bacterial and fungal diversity in tropical soils and microbial community dynamics are underexplored. Isolation techniques aimed at Actinomycetes generally employ highly selective media, powerful antibiotics and antifungal compounds to suppress undesirable bacteria and fungi. However some soil fungi may show their resistance towards these antifungal compounds. During our work to explore soil actinomycetes diversity, slides coated with Arginine Vitamin agar (AVA) incorporating a cocktail of antibiotics and antifungal compounds such as Nystatin, Cycloheximide, Terbinafin, Griseofulvin, and Fluconazole were exposed to soil environment and were retrieved at intervals of 4, 7, 15 and 28 days for detail microscopic studies of surface colonies. Along with actinomycetes the presence of unidentified aseptate and septate fungi was revealed indicating their resistance to combination and concentration of antifungals. Heat treatment of the soil was found to cause considerable decrease in fungal contamination probably due to elimination of heat labile fungi. Our results have led us to develop a simple procedure to sample the interesting and industrially useful strains of soil fungi resistant to common antifungal compounds. Some fungal strains are reported resistant to certain antifungals with resulting therapeutic failures as use of these antifungals inevitably selects resistant fungi, thereby pressing the urge for continuing and cyclical need of new antifungals (Augustin et al., 2004). This technique could prove useful to detect novel antifungal resistant strains with potential to emerge as novel human pathogens. It has not escaped our notice that the probability of such finding could also help to verify whether these fungi could utilize such antifungal compounds through use of hitherto undiscovered metabolic pathways and novel enzymes leading to identification of genes responsible for antifungal resistance.