High-performance thin layer chromatography profiling and antimicrobial activity of Lobostemon fruticosus (L.) H.Buek

Lobostemon fruticosus (L.) H.Buek is a woody, evergreen shrub native to South Africa’s Cape region. Traditionally, the aerial parts of this plant have been used by indigenous communities to treat various skin ailments. While previous studies have documented the chromatographic profiles of the plant’s secondary metabolites and identified key marker compounds for quality control, there has been no prior investigation into the chemotypic variation across different populations of this species. This study aimed to compare the chemical profiles of aqueous methanolic extracts ( n =24) collected from eight distinct South African locations using high-performance thin layer chromatography (HPTLC), and to assess their antimicrobial activity against seven skin-related pathogens. The extracts (80% aqueous methanol) prepared from the aerial parts were profiled using a semi-automated HPTLC system. Distinct bands were isolated, dissolved in methanol, and analysed using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) for compound identification. Antimicrobial activity was evaluated using the broth microdilution method against Staphylococcus aureus, S. epidermidis, S. haemolyticus, Enterobacter hormaechei, Streptococcus pyogenes, and Pseudomonas aeruginosa . The HPTLC profiles were largely consistent across populations, with globoidnan A and B, rabdosiin, rosmarinic acid, and rutin identified as major compounds, showing quantitative variation among the samples. This variation was confirmed by UPLC-MS analysis in tandem with chemometrics, where subtle chemotypic variation was observed (R 2 X cum =0.496). Moderate antimicrobial activity was observed against all tested pathogens, with minimum inhibitory concentrations (MICs) ranging from 2 to 4 mg/mL. These results highlight the need for further research on this medicinal plant. Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany