Characterization and Antibacterial Activity of Soil Actinomycetes from Diverse Land Use Systems in Meru South, Eastern Kenya

Aim: The increasing emergence and global spread of antibiotic-resistance by microorganisms pose a severe public health threat. Continuous exploration of different environments is required to find new sources of antibacterial compounds. Therefore, the study isolated, characterized and identified potential Actinomycetes candidates with antibacterial activity against bacterial pathogens from diverse land use systems.

Study Design: Soil samples from land use systems were collected using a cross-sectional survey technique using line transect sampling in order to isolate Actinomycetes. A 30 × 7× 3 factorial experiment with a completely randomized design was used for evaluating Actinomycetes isolates with antibacterial activity.

Methodology: The in-vitro cultivation of Actinomycetes was evaluated using four selective media. The Actinomycetes isolates were characterized using morphological, biochemical, and molecular markers. The antibacterial activity screening of crude extracts was conducted against six bacterial pathogens using the agar well diffusion method. The antibacterial activity of Actinomycetes isolates were analyzed using Analysis of Variance. The molecular identification was performed using 16S rRNA sequence homology.

Results: The morphological analysis showed variations in colony morphology, including differences in color, size, and texture. Biochemical tests provided insights into the metabolic capabilities of the isolates, indicating variations in enzymatic activities and substrate utilization. Antagonistic activity of Actinomycetes extracts exhibited significant differences (P =.05) against test bacterial pathogens. Notably, isolate C52 from degraded forest zone showed the highest antibacterial activity against Staphylococcus aureus (12.21 mm), isolate L6 (16.23 mm) against Listeria monocytogenes and isolate C50 (15.5 mm) against Raoutella planticola. Streptomyces celluloflavus, S. griseobrunneus, S. pratensis, S. crystallinus, and S. eurocidicus were identified in the study.

Conclusion: The crude extracts obtained from Actinomycetes showed significant antibacterial activity against the selected test organisms. This suggests the presence of bioactive compounds with potential antibacterial properties within these extracts.