Isolation And Characterization of Actinomycetes from Land Use Systems in Meru South Sub-County, Kenya and Screening Their Antibacterial Activities

Abstract

To combat the growth of multidrug resistance to existing antibiotics, the quest for novel bioactive compounds from Actinomycetes in virgin environments has become increasingly crucial. In this study, Actinomycetes were isolated, characterized, and tested for antibacterial activity from the land use system in the Meru South sub-county, Eastern Kenya. Using morphological, biochemical, and molecular techniques, Actinomycetes were described after being cultivated on Starch Casein Agar, Luria Bertani (M1), and International Streptomyces Project Medium (ISP-1 and ISP-4). The isolates were tested for their ability to combat the following six pathogenic bacterial strains; Staphylococcus aureus (ATCC 25923), Listeria monocytogenes (NCTC 11994), Streptococcus mitis (NCTC 12261), Escherichia coli (ATCC 25922), Vibrio furnissii (NCTC 11218), and Rauotella planticola (NCTC 19528). Further identification of potential isolates was done based on 16S rRNA gene sequence analysis. Phylogenetic analysis was done using Molecular Evolutionary Genetics Analysis (MEGA X), and a phylogenetic tree constructed using the Neighbor-Joining methodThe results for morphological characters showed that isolates’ morphology colours ranged from grey to purple to pink to brown to yellow to red to cream- white. The biochemical examination revealed that the majority of them were gram-positive, capable of hydrolyzing starch, urea,casein, and lipase. Few isolates were positive for the cellulose and catalase test. The antibiotic activity of the Actinomycetes isolates against Listeria monocytogenes varied significantly (p=0.05) among them. In comparison to standard streptomycin (16.3mm), isolate L6 (16.23mm) demonstrated the strongest antagonistic activity against L. monocytogenes, followed by isolates C50 (15.5mm) and C52 (12.25mm) against Raoultella planticola. In the phylogenetic tree created using the combined sequences and neighbour joining, isolate P4 was shown to be associated with Streptomyces celluloflavus, isolate C45 with Streptomyces griseobrunneus, isolates Pxiv and C8 with Streptomyces pratensis, isolate P1b with Streptomyces crystallinus, and isolates C10b, C10a, and C3 (Streptomyces eurocidicus). This study shows soil Actinomycetes obtained from land use system in Meru South sub- County has antibacterial activity and may be useful in biomedical applications.