Antimicrobial Metabolites Profile and Inhibitory Activity of Streptomyces xinghaiensis-OY62 Isolated from Soil against Indicator Strains

Aims: The aims of this study were to screen for potential broad-spectrum antimicrobial-producing actinomycetes from the tropical rain forest of Oyo State, Nigeria, to assess the effects of cultural conditions on antimicrobial metabolites, characterize the metabolites and determine its antimicrobial activity against indicator strains.

Place and Duration of the Study: Department of Microbiology, University of Ibadan, Ibadan, between April 2014 and August 2016.

Methodology: Ten soil samples were purposively collected between April and June 2014 for the isolation of Actinomycetes. The isolated strain was identified culturally and molecularly using 16S rDNA. The effect of cultural parameters on antimicrobial activity was done by a standard method. The antimicrobial metabolites were produced by submerged fermentation. Partial purification was carried out by column chromatography. Chemical characteristics of the metabolites were determined by Fourier transformed infra-red spectrometer (FTIR) and gas chromatography coupled with a mass spectrometer. The antimicrobial activity was done by agar well diffusion and macro broth dilution.

Results: Isolate OY62 had broad-spectrum antimicrobial activity and it was identified using its 16S rDNA gene as Streptomyces xinghaiensis-OY62 (KU934248). The highest antimicrobial activity against indicator strains was recorded between pH 7 and pH 8, 0.8% (w/v) sodium chloride, at elevated temperature 55°C, casein+KNO3 as a nitrogen source, starch or absence of carbon source and incubation period of fifteen days. Aliphatic alkene, hydroxyl, carboxylic acids, amides and carbonyls were functional groups detected while thirteen antimicrobial metabolites were characterized. The MIC against indicator strains was between 6.25 mg/L to 12.5 mg/L. Streptomyces xinghaiensis-OY62 exhibited broad-spectrum activity against indicator strains.

Conclusion: The observed results showed that potential broad-spectrum antimicrobial-producing strains of Streptomyces could be isolated from the soil of southwestern Nigeria, which could be useful in the production of antimicrobials that can inhibit the growth of resistant pathogens, reduce microbial infections and death.