Background & Objective: Staphylococcus aureus and Salmonella typhimurium are among important causes of infection and antibiotic resistance. It is essential to find antimicrobial compounds against them. The objective of this study is to evaluate the antibacterial activity of Lecanora muralis SP. extracts on Staphylococcus aureus and Salmonella typhimurium in in-vitro and in animal model.

Materials & Methods: In this study, aquatic, acetonic, and ethanoic extracts of Lecanora muralis SP. were prepared. Then their antimicrobial effects were determined by agar well diffusion method. Minimum Inhibitory Concentration (MIC) and Minimum Bacterial Concentration (MBC) were calculated by macro dilution method. In animal model, 24 hours after inoculation of bacteria in mice, care was provided by injecting 0.5 ml of Lecanora muralis SP. extracts (as MBC concentration).. Then, the colonies of mentioned bacteria in spleen were counted on agar media after nine days.

Results: The results indicated that MIC of acetonic extract of Lecanora muralis SP. for Staphylococcus aureus and Salmonella typhimurium were 103.75 and 207.5 mg/ml and for ethanoic extract were 49.81 and 99.625 mg/ml, respectively. The aquatic extracts of the tested lichens didn't show any antibacterial activity on mentioned organisms. The mean of the bacterial count in experiment group showed significant reduction compared to the control group in animal model.

Conclusion: The ethanoic extract of Lecanora muralis SP. had the most effective antimicrobial activity on Staphylococcus aureus and Salmonella typhimurium in comparison with acetonic extract. In addition Salmonella typhimurium was more sensitive to extracts.