Antibacterial, antioxidant, anti-inflammatory activities and skin irritation side effects of Spirostachys africana stem-bark extracts used traditionally for child skincare by isiXhosa communities in South Africa

Abstract

Spirostachys africana Sond. belongs to the Euphorbiaceae family. It is extensively used in South African traditional medicine to address skin conditions. It is locally known as ``tamboti'' or ``umthombothi''. The microdilution method was used to evaluate the antibacterial activity of the PE, petroleum ether; DCM, dichloromethane; EtOH, Ethanol; DH₂O, distillied water of S. africana stem-bark extracts against Klebsiella pneumoniae (ATCC 13883), Escherichia coli (ATCC 11775), and Staphylococcus aureus (ATCC 12600). The results revealed potent antibacterial activity, particularly in DCM and EtOH extracts, with MIC values ranging from 0.19 to 1.56 µg/ml. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay revealed potent radical scavenging activity, with an EC₅₀ value of 83.26 ± 1.22 μg/ml and a 72.60 ± 0.24 % at the highest tested concentrations. The anti-inflammatory activity of extracts was evaluated via the 15-lipoxygenase (15-LOX) inhibitory and the nitric oxide (NO) inhibition assays using lipopolysaccharide (LPS)-activated RAW 264.7 murine macrophages. The antioxidant activity of the extracts was performed using radical scavenging DPPH (2,2-diphenyl-1-picrylhydrazyl) and electron reducing ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) assays. Water and ethanol stem-bark extracts of S. africana were evaluated for their skin irritation potential using a single application test on rats. The positive control (1 % sodium lauryl sulfate) exhibited significant skin irritation, while the negative control (deionized water) showed minimal irritation. The ethanol extract demonstrated moderate skin irritation potential, with visual scores reaching around 1.5–1.6 after 72 h. This study contributes to the growing body of indigenous medicinal plants and highlights the importance of further exploring natural sources of bioactive compounds for the development of effective and accessible treatments, particularly for vulnerable populations in resource-limited settings.