Isolation and Characterization of Antibiotic Producing Actinomycetes from Soils of Hawassa, Southern Ethiopia

Abstract

Antimicrobial resistance has increased drastically in recent years in developing countries, and it has leading public health concern. With almost all organisms becoming multidrug-resistant to the commonly used antibiotics, there is a need to search for more drugs that are novel in order to address this challenge. Actinomycetes are considered as one of the most diverse groups of filamentous bacteria capable of thriving into different types of ecological niches due to their bioactive potential. Therefore, this study was aimed at isolation and characterization of Actinomycetes from 20 soil samples that were collected from different sites in Hawassa city, Southern Ethiopia. The Actinomycetes were isolated using serial dilution followed by spread plate techniques and antimicrobial activity screening done using modified agar disc diffusion method. Actinomycete Isolation Agar (AIA) was used to isolate Actinomycetes. A total of twenty-nine different Actinomycetes, identified as AB1-AB29, were isolated. They were differentiated based on the difference in appearance of the colony morphology and mycelial structure. Their metabolites were tested for antibiotic activities through the primary screening using modified agar disk diffusion methods. Test bacteria were; E.coli, Klebsiella pneumoniae, Staphylococcus aureus, Shigella boydii and Salmonella typhi. Actinoycete isolates with broad-spectrum activity were further tested against Methicillin-resistant Staphylococcus aureus(MRSA) using modified agar disk diffusion methods. Out of 29 isolates, 19(65.5%) Actinomycetes showed antimicrobial activity against selected bacterial pathogens. Most of the isolates (84.2%) showed good antimicrobial activity against Salmonella typhi though significantly lower than the control drug Ciprofloxacin. Maximum zone of inhibition was 29.2mm observed against S.typhi. As the result indicates the Actinomycetes isolates showed higher inhibition zone against Gram-negative bacteria than Gram-positive bacteria. The study indicated that soils of Hawassa may have potential group of Actinomycetes with broad-spectrum antimicrobial activity. It is therefore suggested that a combination of several molecular analysis methods such as DNA re-association and PCR-based fingerprinting techniques may extremely help to provide broader information about the total genetic diversity of soil Actinomycetes obtained in this study.