Antibacterial Potential of Rhizosphere-Derived Actinomycetes from Millet (Pennisetum glaucum) in Jalingo, Nigeria

This study assessed antibiotics produced from actinomycetes isolated from the rhizosphere of millet plants. Soil samples were collected from the rhizosphere of millet plants grown in agricultural fields within Jalingo metropolis. Each sample was collected from the top 10-15 cm of soil surrounding the millet roots to ensure the inclusion of the rhizosphere microbiome. Soil samples were air-dried and sieved through a 2 mm mesh. Actinomycetes were isolated using Actinomycete Isolation Agar. Isolates showing significant antibacterial activity in preliminary screening were subjected to secondary screening. The antibiotic activity was confirmed using well-diffusion assays. Antibiotics were extracted from the culture broth sediment after centrifugation. Streptomyces spp. displayed higher antibiotic activity, particularly on Day 21, with inhibition zones of 35 mm, 50 mm and 20 mm for E. coli, Salmonella sp. and Staphylococcus aureus respectively. Nocardia spp. demonstrated moderate activity only on Day 14 and 21 and similarly Micromonospora sp. This study demonstrates the antimicrobial potential of Streptomyces spp. and Nocardia spp. against clinically significant pathogens, including Salmonella spp., Staphylococcus aureus, and Escherichia coli. While both Actinomycetes exhibited measurable inhibition, Streptomyces spp. generally showed higher efficacy against Salmonella spp. and E. coli, whereas Nocardia spp. was more effective against S. aureus.