Screening of Actinomycetes from Soil for Antibacterial Activity

Abstract

Actinomycetes are Gram positive, free living saprophytes which are distributed in soil as one of the major populations and are primary source of antibiotics. This study was carried out with a quest to isolate actinomycetes from soil samples of different places and assess their antibacterial activity. Isolation of actinomycetes was carried out by serial dilution of soil sample followed by spread plate method. The antimicrobial extract was extracted using ethyl acetate. Assessment of antimicrobial activity was performed by using Agar cup plate assay against test organisms (Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Salmonella paratyphi, Bacillus subtilis, Staphylococcus aureus). Antibacterial activity was tested against Methicillin Sensitive Staphylococcus aureus and Methicillin Resistant Staphylococcus aureus in the isolates having effective inhibitory activity against Staphylococcus aureus. From 15 soil samples of 12 different locations, 121 actinomycetes isolates were isolated. Among them, 58 (47.9%) isolates were inhibitory against at least 1 test organism in primary screening, of which 22 isolates effective against more than 1 test organism was chosen for secondary screening. Out of them, 8 were inhibitory against 2 test organisms while 14 were inhibitory against 3 test organisms. Staphylococcus aureus was found to be the most susceptible test organism with its susceptibility against 12 actinomycetes isolates. Among 12 isolates effective against Staphylococcus aureus, 10 were found to have an inhibitory effect against Methicillin Susceptible Staphylococcus aureus while 6 were found to have inhibitory effect against Methicillin Resistant Staphylococcus aureus strain. The findings of this study highlight the inhibitory potential of actinomycetes and the need for further investigation for obtaining novel antimicrobial agents from actinomycetes from various unexplored areas.

Antimicrobial Potential of Streptomyces spp. Isolated from the Rift Valley Regions of Ethiopia

“…Therefore, it is an urgent need for searching new, potent, and broad-spectrum antimicrobial agents against infectious pathogens from microbial sources [ 7 ]. Actinomycetes especially Streptomyces have proven potential to produce bioactive compounds and are the richest sources of secondary metabolites including novel antibiotics [ 8 – 10 ]. Thus, exploration of bioactive metabolite compounds for potential use in biotechnological, agricultural, and biopharmaceutical applications from actinomycetes isolated from unexplored and extreme environments has required considerable attention.…”

“…niger ATCC10535). This indicated that the occurrence of actinomycete isolates with antimicrobial activity in the current research region was higher than 45.3% [ 8 ] and lower than 71.9% [ 12 ]. These relatively high proportions of numbers of isolates from the study area suggest that samples of the Rift Valley of Ethiopia have a high potential for the isolation of actinomycetes having antimicrobial activity.…”

“…Currently, the majority of the commercially and medically known antibiotics have originated from a different genus of actinomycetes [ 6 , 7 ]. Actinomycetes have also been the source of many industrially and clinically important bioactive metabolites in treating cancer, inflammatory diseases, allergies, anthelmintics, autoimmune diseases, infections, and others [ 8 , 9 ]. Among actinomycetes genera, Streptomyces are the largest genus and the most frequent producer of antibiotics which is continuously being explored for antimicrobial drug discovery [ 9 , 10 ].…”

Isolation and extraction of some compounds that act as antimicrobials from actinomycetes

“…Following the formation of colonies, they were sub-cultured in a test tube containing SCA slants, incubated at 28 °C for 7 days, and then kept in the fridge as the stock. To prevent the cultures from dying out, the isolates were subculture again every 2–3 weeks ( Budhathoki and Shrestha, 2020 ).…”

“…The colony of selected actinomycetes that showed the most activity against test organisms in primary screening was cut from their pure culture and placed in the broth. For 8 days, the conical flasks were placed in a rotary shaker incubator at 28 °C ( Budhathoki and Shrestha, 2020 ).…”