Abstract
In vitro screening of antibacterial and antifungal activities of hexane, chloroform, ethyl acetate, methanol and water extracts of selected promising actinomycetes strains were studied towards Gram-positive, Gram-negative bacteria, dermatophytes and opportunistic pathogens. Crude antimicrobial metabolites were extracted by liquid-liquid extraction and solid-liquid extraction method using hexane, chloroform, ethyl acetate and methanol. The lowest minimum inhibitory concentration (MIC) of the extracts was assessed by the broth micro dilution method. All the extracts obtained from eight strains showed promising activity against tested Gram-positive bacteria. The hexane extracts of strain ERI-1 exhibited activity against Bacillus subtilis, Staphylococcus aureus and Staphylococcus epidermidis at a concentration of 5 mg/ml. Ethyl acetate extract of strain ERI-4 showed MIC of 5 mg/ml but S. epidermidis and S. aureus. B. subtilis exhibited activity at 2.5 mg/ml. However, ethyl acetate and lyophilized water extract of strain ERI-3 inhibited the growth of Trichophyton mentagrophytes, Trichophyton rubrum, Epidermophyton floccosum and Scropulariopsis sp at 10 mg/ml. Overall significant antibacterial and antifungal activities were noted in the ethyl acetate extract of ERI-1 and ERI-3. Methanol extract of ERI-26 exhibited good antibacterial and antifungal activities. Key words: Actinomycetes, organic extracts, minimum inhibitory concentration (MIC), antimicrobial activity.
Highlights
Actinomycetes are Gram-positive bacteria showing a filamentous growth
This study focused on the extraction of antimicrobial metabolites by using different solvents and evaluates minimum inhibitory concentration by broth micro dilution method
The spore suspensions of the culture were inoculated on Modified Nutrient Glucose Agar (MNGA) media and incubated at 28oC for six days
Summary
Actinomycetes are Gram-positive bacteria showing a filamentous growth. Gram positive filamentous bacteria are widely distributed in a variety of natural and man-made environments, constituting a significant component of the microbial population in most soils. Most of metabolites are produced from Streptomyces. 75% of metabolites originated from Streptomyces genus and at least 5000 documented bioactive compounds are known as being produced by Streptomyces genus (Vasanthabharathi et al, 2011). In searching for new antibiotics, number of different bacteria, actinomycetes, Streptomycetes, fungi and algae have been investigated. Extraction of antimicrobial metabolites from Streptomyces and its antimicrobial effects on bacteria and fungi were studied. Nutrients required for the antimicrobial compounds production were optimized under the shake flask condition for the identified Streptomyces strains (Arasu et al, 2012; 2013). This study focused on the extraction of antimicrobial metabolites by using different solvents and evaluates minimum inhibitory concentration by broth micro dilution method
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