Phytochemical screening and antibacterial activity of Centaurea senegalensis growing in Nigeria

Abstract

The increasing prevalence of drug resistant pathogens in developing countries has necessitated research for effective therapeutic agents from plants. This study was designed to evaluate the antibacterial properties of Centaurea senegalensis and investigate the phytochemical constituents. The plant sample was extracted using methanol and subjected to successive partition with n-hexane, dichloromethane and ethyl acetate. The methanol extract (ME), hexane (HF), dichloromethane (DF) and ethylacetate (EF) fractions were subjected to antibacterial screening on selected gram-positive and gram-negative bacteria using agar well and micro broth dilution methods. The antibacterial efficacies of extracts showed varying zones of growth inhibitions (15-31 mm). The DF fraction was effective on Methicillin resistant Staphylococcus aureus (MRSA), and Vancomycin resistant enterococci (VRE) with interesting activity (28 mm, MIC 12.5 mgmL^-1). However, the EF was most effective fraction against gram-negative bacteria such as Escherichia coli (31 mm, MIC, 12.5 mgmL^-1). Chemical composition of bioactive fraction was determined using gas chromatography-mass spectrometry (GC-MS). The compounds detected were largely natural acetylenes such as 1, 5-heptadien-3-yne (23.2%), 2-hexyne-1-ol (12.3%), 2-methyl-1,5-hexadien-3-yne (6.6%) and 5-methyl-1-hexyn-3-ol (2.1%) as most abundant phytoconstituents identified. C. senegalensis fractions have demonstrated effective activity on both gram-positive and gram-negative bacteria, which might be attributed to acetylene derived natural compounds. Our findings have shown the importance of C. senegalensis as source of chemical compounds with effective antibacterial properties.

Keywords: Centaurea senegalensis, phytochemical screening, antibacterial activity, GC-MS