Production of a growth dependent metabolite active against dermatophytes by Streptomyces rochei AK 39.

BACKGROUND & OBJECTIVE: Dermatophytes responsible for causing dermatophytoses in humans have acquired resistance to certain antimycotic drugs. We isolated naturally occurring actinomycetes with an ability to produce metabolites having antimycotic property. The timecourse of antifungal metabolite production in terms of arbitrary units (AU) under optimum conditions was studied. METHODS: Water and soil samples were collected from various locations. The actinomycetes were isolated on starch casein medium and screened for their antifungal activity against yeasts and molds including dermatophytes. One promising isolate which showed a unique, stable and interesting property of inhibiting only dermatophytes was selected and characterized. Optimization of antifungal metabolite production in terms of AU using Trichphyton rubrum as target was done. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values of the culture supernatant from the isolate and that of griseofulvin were determined for all dermatophytes. RESULTS: Of the 218 actinomycete isolates, 14 per cent produced the metabolites having antifungal activity. The selected actinomycete, identified as Streptomyces rochei AK 39 produced metabolite, which was active against only dermatophytes whereas yeasts and other molds were resistant to it. Starch casein medium was found to be good for inducing antifungal activity in the isolate. The maximum antifungal metabolite production (400 AU/ml) was achieved in the late log phase, which remained constant during the stationery phase, and it was extracellular in nature. The MIC and MFC values of the culture supernatant from the isolate against the dermatophytes were within the range 1.25 to 5 and 1.25 to 10 AU/ml respectively. INTERPRETATION & CONCLUSION: The metabolite from Streptomyces rochei AK 39 was produced during late log phase and was active against only dermatophytes with a greater potency than griseofulvin. However, this needs further investigation using purified powdered form of the active component.

A non-polyene antifungal antibiotic from Streptomyces albidoflavus PU 23.

In all 312 actinomycete strains were isolated from water and soil samples from different regions. All these isolates were purified and screened for their antifungal activity against pathogenic fungi. Out of these, 22% of the isolates exhibited activity against fungi. One promising strain, Streptomyces albidoflavus PU 23 with strong antifungal activity against pathogenic fungi was selected for further studies. Antibiotic was extracted and purified from the isolate. Aspergillus spp. was most sensitive to the antibiotic followed by other molds and yeasts. The antibiotic was stable at different temperatures and pH tested and there was no significant loss of the antifungal activity after treatment with various detergents and enzymes. Synergistic effect was observed when the antibiotic was used in combination with hamycin. The antibiotic was fairly stable for a period of 12 months at 4 degree C. The mode of action of the antibiotic seems to be by binding to the ergosterol present in the fungal cell membrane resulting in the leakage of intracellular material and eventually death of the cell. The structure of the antibiotic was determined by elemental analysis and by ultraviolet (UV), Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and liquid chromatography mass spectra (LCMS). The antibiotic was found to be a straight chain polyhydroxy, polyether, non-proteinic compound with a single double bond, indicating a nonpolyene antifungal antibiotic.

Isolation, characterization and optimization of antifungal activity of an actinomycete of soil origin.

About 312 actinomycetes were isolated from soil samples on chitin agar. All these isolates were purified and screened for their antifungal activity against pathogenic fungi. Out of these, 22% of the isolates exhibited activity against fungi. One promising isolate with strong antifungal activity against pathogenic fungi was selected for further studies. This isolate was from Pune, and was active against both yeasts and molds. Various fermentation parameters were optimized. Based on morphological and biochemical parameters, the isolate was identified as Streptomyces. The correlation of antifungal activity with growth indicated growth dependent production of antimetabolite. Maximum antifungal metabolite production (600 units/ml) was achieved in the late log phase, which remained constant during stationery phase, and it was extracellular in nature.