Antibacterial, antiquorum sensing, antibiofilm activities and chemical profiling of selected South African medicinal plants against multi-drug resistant bacteria

Abstract

South African indigenous plants have been predominantly studied for their antibacterial abilities, overlooking their antipathogenic and antivirulence (also known as antiquorum sensing) potential. Hence, this study explored the selected medicinal plants as possible agents capable of interfering with bacterial growth, quorum sensing and biofilm formation and identified their respective bioactive compounds. Ten medicinal plants were extracted with varied solvents. Melianthus comosus (dichloromethane, aqueous and methanol), Pelargonium sidoides (aqueous) and Vachellia karroo (aqueous and methanol) extracts showed potent minimum inhibitory concentration values ranging from 0.19 to 0.78 mg/ml against the tested bacterial pathogens: Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, and Escherichia coli. Reduced violacein production (up to 38.34%) in Chromobacterium violaceum was noted for Melianthus comosus, Plectranthus ecklonii and Pelargonium sidoides extracts. Treatment of five MDR bacterial pathogens with active extracts for anti-adhesion and biofilm development showed up to 66.34 and 31.82% inhibitory effects, respectively. Chemical characterization of active extracts revealed compounds such as α-D-glucopyranoside, methyl, linalool, octadecanoic acid and hexadecanoic acid. The biological assays validated the tested plant extracts as having antibacterial and antipathogenic potentials that could be used against multidrug resistant bacteria. Key words: Antibacterial activity, biofilm inhibition, chemical characterization, multidrug resistance, phytochemicals, quorum sensing inhibition.