Evaluating the Synergistic Antibacterial Effects of Rosa damascena and Hibiscus sabdariffa Extracts on E. coli

The emerging global issue of antibiotic-resistant Escherichia coli has prompted increased interest in plant-based antimicrobials and potential synergistic combinations as an alternative to traditional and synthetic antibiotics. The purpose of the study was to evaluate whether the combined extracts of Hibiscus sabdariffa and Rosa damascena exhibit stronger antimicrobial properties than each extract alone against E. coli. It was hypothesized that the combined extracts of Rosa damascena and Hibiscus sabdariffa would produce a greater zone of inhibition against E. coli K-12 than either extract alone because of synergistic interactions between their bioactive compounds. Three solutions of Hibiscus sabdariffa (roselle) extract, Rosa damascena (damask rose) extract, and a mixture of 50 mL of R. damascena extract and 50 mL of H. sabdariffa extract (1:1 ratio) were prepared. The control group consisted of bacteria with no extract applied. Thirty sterile diffusion discs were soaked in each of the commercial alcohol-free liquid plant extracts, which were placed in the center of each section on the Mueller–Hinton agar plates inoculated with E. coli K-12 and incubated at 37 °C for 18 hours. Following incubation, no observable zone of inhibition was formed in any of the trials. It was determined that the most likely cause of error arose from using commercial alcohol-free extracts, which may have reduced potency, suggesting that freshly prepared extracts in organic solvents have the potential to produce more accurate antibacterial results.