Bioassay-guided detection of antimicrobial components from Sutherlandia frutescens and Salvia Africana-lutea

Abstract

Plants remain beneficial to humans and have been used as a source of medicine for various ailments including infections. Salvia africana-lutea and Sutherlandia frutescens are endemic to South Africa and have been traditionally used to treat and manage a wide variety of infections including respiratory, urinary tract and skin infections, Human Immunodeficiency Virus, coughs and cancer. Many scientific studies have confirmed some of these medicinal activities. The current study sought to investigate antibacterial properties of Salvia africana-lutea and Sutherlandia frutescens. To determine the respective minimum inhibitory concentrations, a thorough investigation of antibacterial activity against bacteria such as Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa was carried out using agar well-diffusion and microdilution assays. Results indicate that Salvia africana-lutea extracts have better antibacterial activity in comparison to Sutherlandia frutescens extracts. The minimum inhibitory concentrations of Salvia africana-lutea extract ranged from 4 to 10mg/ml. When compared to Sutherlandia frutescens, which had very poor antibacterial activity; the aqueous, ethanol, and acetone extracts from Salvia africana-lutea showed good antibacterial activity against Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis. Salvia africana-lutea extracts however had little to no antibacterial activity against Pseudomonas aeruginosa. Phytochemical techniques, such as Thin-Layer Chromatography, Bioautography, Nuclear Magnetic Resonance Spectrometry, and Liquid-Chromatography Mass Spectrometry were employed to detect and possibly identify the active fractions/compounds. A few compounds (relative to rosmarinic acid) were identified in acetone and ethanol extracts of Salvia africanalutea. By identifying active compounds against medically significant microbes, this study adds a layer of gravitas to the already existing knowledge on medicinal properties of Salvia africanalutea. Outputs of this research may provide leads to possible new drug formulations and preparations that might help control and reduce the burden of infections.