The effectiveness of antimicrobial drugs becomes uncertain due to the emergence of multidrug resistant microorganisms, which highlights the need for alternative antibacterial agents. Natural products are of great importance in the search for biologically active compounds. The present study aimed at investigating the antibacterial properties of propolis, one of the natural bee products, against S. aureus, P. aeruginosa and E. coli. Propolis was extracted using 30 %, 50 %, 70 %, and 99.9 % ethanol. The in vitro antibacterial activities of propolis extracts were evaluated by the disc diffusion method with concentrations between 500 and 4000 µg/ml. Among the extracts, the 50 % and 70 % propolis extracts showed strong antibacterial activity against all tested strains with inhibition zones ranging from 6.64 ± 0.15 to 11.99 ± 0.04 mm. P. aeruginosa was sensitive strain to the ethanolic extracts of propolis with the highest inhibition zone diameter of 11.99 ± 0.04 mm. Statistically significant differences in growth inhibition were observed among the types of extracts (30 %, 50 %, 70 % and 99.9 %) against P. aeruginosa (p < 0.05) and E. coli (p < 0.05), but the effect was not significant on S. aureus (p > 0.05). All propolis extracts showed no effect on S. aureus at concentrations below 2000 μg/ml. Propolis extracts showed a lower zone of inhibition compared to the effect demonstrated by the positive control. Overall, the results indicate that ethanolic extracts of Ethiopian propolis has a promising antibacterial activity which could be of an antibiotic development benefit.
Antibacterial Activity, Disc Diffusion Method, Ethiopia, In vitro, Propolis