Evaluation of extracts and essential oil from Callistemon viminalis leaves: Antibacterial and antioxidant activities, total phenolic and flavonoid contents

Objective: To investigate antioxidant and antibacterial activities of Callistemon viminalis (C. viminalis) leaves. Methods: The essential oil of C. viminalis leaves obtained by hydro distillation was analyzed by GC/MS. Different extracts were tested for total phenolic and flavonoid contents and in vitro antioxidant (DPPH assay) and antibacterial (agar disc diffusion and 96 well micro plates methods) actives. Results: Fourteen components were identified in the essential oil, representing 98.94% of the total oil. The major components were 1,8 cineole (64.53%) and alpha-pinene (9.69%). Leaf essential oil exhibited the highest antioxidant activity of (88.60 +/- 1.51)% comparable to gallic acid, a standard compound [(80.00 +/- 2.12)%]. Additionally, the biggest zone of inhibitions against the studied bacterial strains was observed by the essential oil when compared to the standard antibiotic (tetracycline). The crude methanol extract and ethyl acetate fraction had a significant antibacterial activity against the tested bacterial strains. Conclusions: It can be suggested that C. viminalis is a great potential source of antibacterial and antioxidant compounds useful for new antimicrobial drugs from the natural basis. The present study revealed that the essential oil as well as the methanol extracts and ethyl acetate fraction of C. viminalis leaves exhibited highly significant antibacterial activity against the tested bacterial strains.