Preliminary Studies on the Bioactivity of Secondary Metabolites from Aureobasidium pullulans and Emericela rugulosa

In the study of searching for bioactive fungal metabolites, crude extracts of Aureobasidium pullulans and Emericela rugulosa were screened in vitro against eleven human pathogens. The production medium changed from slightly basic (pH 7.21) to slightly acidic (pH 6.72) as fermentation progressed till the 12th day. The wet biomass of the fungal mycelia as well as the dry weights of the crude extracts increased while the amounts of glucose in the growth medium reduced with a corresponding increase in incubation period. Contact bioautographic assay showed that the extracts exhibited broad-spectrum antimicrobial potency. Activity against some human pathogenic organisms including Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella typhi) and fungal strains (Candida albicans, Trichophyton concentrum, T. mentagrophytes, T. rubrum and T. torulans) is discussed. Bioactivity of the extracts, as depicted by zones of inhibition in agar well diffusion assay, was found to increase as the fermentation days increased, irrespective of the fungal biosource of the metabolites. In most studies, A. pullulans grew faster and caused higher inhibition than E.rugulosa.