Antibacterial and ciprofloxacin modulating activity of Ptaeroxylon obliquum (Thunb.) Radlk leaf used by the Xhosa people of South Africa for the treatment of wound infections

Abstract

The present work investigated the antibacterial activity of Ptaeroxylon obliquum leaves (POL) extracts in the presence or absence of ciprofloxacin by the broth microdilution method and time–kill assay against bacterial strains associated with wound infections. Free-radical–scavenging activity (FRSA) was determined using the stable 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) bioassay method. The chemical composition of the most active antioxidant extract was analysed using a gas chromatograph interfaced with a mass spectrometer (GC-MS). All POL extracts showed good antibacterial activity against the bacterial strains, with a minimum inhibitory concentration (MIC) ranging from 4 to 128 µg/mL. The exposure of bacterial strains to POL extracts resulted in 2–64-fold reductions in the MIC of ciprofloxacin. Correspondingly, the time–kill curves showed that combined POL extracts and ciprofloxacin treatment inhibited bacterial growth below the lowest detectable limit after 24 h of incubation. Furthermore, the ethanol extract from P. obliquum (POE) had the highest total flavonoids content (TFC: 62.7 mg/quercetin equivalent/g), while the methanol extract of P. obliquum (POM) had the best total phenolic content (TPC: 275 mg/quercetin equivalent/g) and DPPH*-scavenging activity having 50% inhibitory concentration (IC50) of 0.125 mg/mL. The chemical composition indicated the presence of aromatic and aliphatic compounds that are known to have a wide biological effect. The findings from this study suggest that POL extracts could be a source of pharmaceutical agents for treatment of skin diseases, wound infections and as putative candidates to modulate the multidrug resistance mechanism.