Antimicrobial Activity of Actinomycetes Isolates from Different Soil Samples in Ikere-Ekiti, Ekiti State, Nigeria

Abstract

Actinomycetes are a group of Gram-positive, facultatively anaerobic soil bacteria known for their ability to produce bioactive substances. This study analysed the antimicrobial potential of Actinomycetes isolates from soil samples collected from various locations within the University campus in Ikere-Ekiti. Samples were serially diluted and cultured on Starch Casein Agar supplemented with Fluconazole and Nalidixic acid antibiotics. Isolates were characterised morphologically and biochemically, followed by primary and secondary screenings for antimicrobial activity using perpendicular-streak and agar-well diffusion techniques. Colony morphology exhibits variation in size, shape, elevation, edge, surface texture, consistency, and pigmentation. Mean total Actinomycetes count ranged from 0.813 to 0.881 log cfu/mL at dilution 10^-2 and 0.378 to 0.602 log cfu/mL at dilution 10^-3. All isolates were Gram-positive, and biochemical tests revealed that approximately 15.4% of the isolates were catalase-positive, while about 33.3% demonstrated indole positivity. The recovered 30 Actinomycetes isolates were screened against eight test organisms: Escherichia coli, Klebsiella sp., Pseudomonas sp., Proteus sp., Streptococcus sp., Staphylococcus sp., Aspergillus flavus and Aspergillus niger. Isolates SB3¹ and DB3 were active against all the test bacteria during primary screening, while isolate SB3¹ showed activity against only four test bacteria during secondary screening. Furthermore, nine out of 27 isolates predominantly exhibited antifungal activity against A. flavus and A. niger during both primary and secondary screening. These findings show the Actinomycetes isolates are a promising source of antimicrobial compounds.