<b>Background and Objectives:</b> Propolis is a natural product derived from plant resins and collected by honeybees to protect the colony against different pathogens. The antimicrobial properties of an ethanolic extract of propolis (EEP) were investigated in this study. <b>Materials and Methods:</b> In the Egyptian Governorate of Giza, F1 carniolan honeybee (<i>Apis mellifera carnica</i> P.) colonies collected propolis in the autumn, spring and summer of 2019-2020. We investigated the antibacterial activity of EEP against Gram-positive <i>B. subtilis</i> and Gram-negative <i>E. coli</i>. Propolis was evaluated and its effects on the amounts of total DNA, RNA and protein in <i>Bacillus subtilis</i> and <i>Escherichia coli</i> were investigated. <b>Results:</b> Propolis inhibited the growth of <i>B. subtilis</i>. At 5% concentration, the inhibition zones were 8.66, 10.66 and 8.52 mm for autumn, spring and summer propolis, respectively, at 10% concentration, they were 19.66, 21.33 and 18.0 mm, respectively. Propolis also inhibited the growth of <i>E. coli</i> at a 5% concentration. The inhibition zones were 3.660, 4.00 and 4.33 mm for autumn, spring and summer propolis, respectively and at 10% concentration, they were 7.65, 8.33 and 7.33 mm, respectively. The inhibition zones were the largest (10.66 and 21.33 mm) for <i>B. subtilis</i> at 5 and 10% propolis, respectively, whereas slightly low inhibition zones (4.0 and 8.33 mm) were observed for <i>E. coli</i> (5 and 10% propolis, respectively) in spring. In <i>E. coli</i> and <i>B. subtilis</i>, propolis inhibited the replication of DNA-dependent RNA polymerase. <b>Conclusion:</b> The study showed that total DNA, RNA and protein levels in <i>B. subtilis</i> were reduced by 40, 15.52 and 52.6%, respectively, whereas those in <i>E. coli</i> were reduced by 12, 15 and 8%, respectively. Furthermore, propolis activity was less effective against Gram-negative bacteria than Gram-positive bacteria.
Keywords: Bacillus subtilis; DNA; Escherichia coli; Propolis; RNA; total protein.