Isolation and screening of antibiotic producing fungi from solid-state waste

Aim: To evaluate the antimicrobial potential of fungal extracts isolated from solid-state waste and study their active constituents. Antibiotics are the most important secondary metabolites produced by the microorganisms that are commercially exploited for the treatment of various diseases worldwide. But with time, these microbial pathogens have become more powerful and resistant to antibiotic treatment, creating new strains that are difficult to control. To overcome the problem of multi-drug resistance, the present study aimed at exploring new sources of bioactive components. Methods: A total of 22 fungal strains were isolated from solid-state household waste dumping site at Hisar, India. The perpendicular streak plate technique was used for primary screening against three test microorganisms (Staphylococcus aureus, Escherichia coli, and Candida albicans). About 55% of the tested fungal strains showed antimicrobial activity against all three tested microorganisms. The positive fungal strains were put to secondary screening by Agar well diffusion assay against eight test microorganisms (Gram positive: Bacillus subtilis, Staphylococcus aureus, Streptococcus gordonii and Gram negative: Pseudomonas aeruginosa, Escherichia coli, Pseudomonas florescens, Salmonella enterica and fungus Candida albicans). Results: The potent fungal strain with maximum zone of inhibition was selected for secondary metabolite extraction with dichloromethane and the crude extracts examined for antimicrobial properties. Analyses of the crude metabolites by thin layer chromatography (TLC) showed the presence of bioactive components with Rf values of 0.88. The results demonstrated that the crude extracts of SSR-16 exhibited great antibacterial activity against all test bacteria with zone of inhibition as 2.2cm against E.coli and P.aeroginosa, 2.0cm against C.albicans, 1.8cm against B.subtilis and P.florescens, 1.6cm against S.aureus and 1.4cm against S.entericus and S.gordoni.   Conclusion: The selected strain SSR-16 was identified as Aspergillus species using 18 S rDNA gene sequence analysis. The study suggests that the selected Aspergillus strain may be a source of potential antimicrobial agents.