Antibacterial and antioxidant activities of extracts and some flavonoids from the leaves of Clerodendrum buchholzii Gurke (Verbenaceae)

Abstract

Morbidity and mortality due to diarrhoea continues to be a major problem in many developing countries. The most common microorganisms responsible for diarrhoeal diseases are Vibrio cholerae, Escherichia coli and Shigella spp. The present study aims to evaluate the antibacterial and antioxidant activities of extracts and compounds from the leaves of Clerodendrum buchholzii, a plant traditionally used in the African pharmacopeia for the treatment of furunculosis, echymosis and gastritis. The dried leaves were macerated in methanol (MeOH) to afford the crude extract that was extracted with ethyl acetate (EtOAc) and n-butanol (n-BuOH) to obtain EtOAc and n-BuOH extracts, respectively. The column chromatography of EtOAc and n-BuOH extracts followed by purification of different fractions led to the isolation of four known flavonoids [acacetin 7-O-β-D-glucoside (1), kaempferol 7-O-β-D-glucoside (2), acacetin (3) and apigenin (4)]. Structures of isolated compounds were assigned on the basis of spectroscopic analysis, and by comparison of our data with those of the literature. The antioxidant activity was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and gallic acid equivalent antioxidant capacity (GEAC) assays. The antibacterial activity was assessed using broth microdilution method by performing minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) against the strains of Gram-positive bacterium, Staphylococcus aureus (a major cause of community and hospital-associated infection), and Gram-negative multi-drug resistant bacteria, Vibrio cholerae (causative agent of cholera) and Shigella flexneri (causative agent of shigellosis). All of the extracts showed different degrees of antioxidant and antibacterial activities. Apigenin (4) obtained from EtOAc extract displayed the largest antibacterial and antioxidant properties which were in some cases equal or higher than those of reference drugs. Our results showed that C. buchholzii has potentials as a natural source of anti-diarrhoeal and free radical scavenging products, and could be given further investigations.

Keywords: Clerodendrum buchhlzii, Verbenaceae, Flavonoids, Antibacterial, Antioxidant