Wild plants can contain bioactive compounds with potential activity against disease-causing microorganisms. In the Kingdom of Saudi Arabia, there are many plant species that may have antibacterial, antifungal, or antiviral activities, among other properties. We extracted bioactive compounds with methanol as well as with water from leaves of Breonadia salicina, which is an endangered plant found in the wild in Saudi Arabia. These extracts were tested against the bacteria Bacillus subtilis, Pseudomonas aeruginosa, Shigella sonnei, Escherichia coli, and Staphylococcus aureus. Both extracts showed antibacterial activity against all of the microorganisms, and thus, B. salicina leaf extract has potential as an antimicrobial agent for the preservation of foods, instead of synthetic chemical compounds. We found that the methanolic leaf extract was more effective than the aqueous crude extract against B. subtilis, P. aeruginosa, and S. aureus.