Antibacterial activity of Dioscorea bulbifera Linn. extract and its active component flavanthrinin against skin-associated bacteria

Abstract

Background Dioscorea bulbifera Linn. has been used for wound care in Thailand. However, a comprehensive evaluation of its antibacterial activity is required. This study aimed to investigate the antibacterial efficacy of D. bulbifera extract against skin-associated bacteria and isolate and characterize its active antibacterial agent, flavanthrinin. Methods Air-dried bulbils of D. bulbifera were pulverised and extracted with hexane, dichloromethane, ethyl acetate, methanol, ethanol, and distilled water; vacuum filtered; concentrated; freeze-dried; and stored at -20 ºC. Antibacterial activity of the extracts was assessed using microdilution techniques against several skin-associated bacteria. Thin-layer chromatography (TLC) bioautography was used to identify the active compounds in the extract, which were fractionated by column chromatography and purified by preparative TLC. The chemical structures of the purified compounds were analysed using nuclear magnetic resonance (NMR). The cytotoxicity of the extract and its active compounds was evaluated in Vero cells. Results The ethyl acetate extract exhibited distinct inhibition zones against bacteria compared to other extracts. Therefore, the ethyl acetate extract of D. bulbifera in the ethyl acetate layer was used for subsequent analyses. D. bulbifera extract exhibited antibacterial activity, with minimum inhibitory concentrations (MICs) of 0.78–1.56 mg/mL. An active compound, identified through TLC-bioautography, demonstrated enhanced antibacterial activity, with MICs of 0.02–0.78 mg/mL. NMR analysis identified this bioactive compound as flavanthrinin. Both D. bulbifera extract and flavanthrinin-containing fraction demonstrated potent antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and S. epidermidis. The flavanthrinin containing fraction demonstrated low cytotoxicity against Vero cells, showing CC50 values of 0.41 ± 0.03 mg/mL. These values are lower than the MIC value, indicating that this fraction is safer than the initial ethyl acetate extract. Conclusions Dioscorea bulbifera extract and its bioactive component flavanthrinin demonstrated significant antibacterial activity against the skin-associated bacteria Staphylococci, including MRSA. Flavanthrinin has potential as a complementary therapeutic agent for managing skin infections owing to its potent antibacterial effects and low cytotoxicity.