Bioassay Guided Fractionation of an Anti-Methicillin-Resistant Staphylococcus aureus Flavonoid From Bromus inermis Leyss Inflorescences

Background: Plants are considered as promising sources of new antibacterial agents as well as bioassay guided fractionation. Objectives: In the present work, the antibacterial properties, especially against methicillin-resistant Staphylococcus aureus (MRSA), of Bromus inermis inflorescence was studied, using the bioassay guided fractionation as well as the bio-autographic method. Materials and Methods: The plant organic extract was prepared via maceration in methanol, followed by the fractionation using n-hexane. The extracts were subjected for minimum inhibitory concentrations (MICs) against some human pathogenic bacteria via standard broth micro-dilution assay. Thereafter, a bio-autographical method was applied using the high performance thin layer chromatography (HPTLC) coupled with agar overlay assays for the primary characterization and identification of bioactive substance (s). Results: Through the bioassay guided fractionation method, the greatest antibacterial activities were related to the n-hexane extract. It was also revealed that the effective anti-MRSA agent of the assessed plant was a relatively polar substance with an MIC value of about 8 mu g/mL against the tested MRSA strain (in comparison with the MIC value of 32 mu g/mL for chloramphenicol). Conclusions: As a result of the full range UV-Vis scanning of the responsible band in the HPTLC experiments (200-700 nm), the flavonoid was the most imaginable natural compound.