Antagonistic Activity of Antimicrobial Producing Bacteria Against Multidrug-Resistant Bacteria Isolated From Hotspot Environments

Background: To overcome antibiotic resistance, there is an interest in improving or discovering novel classes of antibiotics from microorganisms that have different mechanisms of action worldwide. In Ethiopia, no significant studies have been conducted to isolate antibiotic-producing bacteria from hotspot environments and evaluate their antagonistic activities against multidrug-resistant bacteria. Therefore, the present study aimed to isolate antibacterial-producing bacteria from wastes and evaluate their antagonistic activities against multidrug-resistant bacteria in Bahir Dar town. Methods: A total of 49 bacteria were isolated from 30 waste and soil samples and tested against multidrug-resistant bacteria by primary screening using the single line streak method. Crude extracts of promising isolates were produced using submerged state fermentation methods and tested against multidrug-resistant bacteria using agar well diffusion methods. The minimum inhibitory and bactericidal concentrations of the crude extracts were determined using two-fold serial dilution and streak plate methods. Results: The results revealed that 11 (22.5%) bacterial isolates showed antibacterial activity against 1 or more tested multidrug-resistant bacteria. Isolates Ampb17 and Ampb33 isolated from soil and poultry waste showed the highest antagonistic activity against Salmonella spp., with a mean zone of inhibition of 20.3 ± 0.3 mm. The crude extract from isolate Ampb30, isolated from dairy waste, showed the highest antibacterial activity against Salmonella spp., with a mean zone of inhibition of 27.7 ± 0.3 mm. One-way analysis of variance confirmed that most of the crude extracts were statistically significant at a 95% confidence interval. The minimum inhibitory concentration of crude extracts was 0.13 mg/ml against S. aureus, E. coli, Salmonella spp., Pseudomonas spp., and Klebsiella spp., whereas the minimum bactericidal concentration of crude extracts was 0.25 mg/ml against S. aureus, E. coli, Salmonella spp., and Pseudomonas spp. Conclusion: The results of the present study revealed that antibiotic-producing bacteria from waste and soil have vast potential sources of antibacterial compounds.