Ethnomedicinal importance and antimicrobial activity of Leonotis ocymifolia

Species of the genus Leonotis (Lamiaceae) are commonly used in Africa as traditional herbal remedies for various ailments such as bronchial illness, epilepsy, stomach aches, and skin diseases. Most of these species are found in South Africa, and Leonotis ocymifolia (Burm.f.) Iwarsson (klipdagga) is one of them. The recorded medicinal uses of L. ocymifolia include treating diabetes, hypertension, anemia, nerve weakness, high blood pressure, poor blood circulation, rheumatism, snakebites, eczema, and several skin infections among others. Little is known about the antimicrobial activity. Therefore, this study aimed to investigate the antimicrobial potential of L. ocymifolia by reviewing the ethnomedicinal importance and antimicrobial potential (Minimum Inhibitory Concentration, Minimum bactericidal concentration, and Time-kill assessment) as well as the toxicity of L. ocymifolia's extracts (DCM: Meth) and fractions (ethyl acetate, hexane, and butanol) against six bacteria and four Candida species. The results demonstrated that all the Candida pathogens tested were susceptible to the extracts, with moderate to noteworthy activity. The n-hexane fraction exhibited the highest antimicrobial activity against all tested pathogens, with mean MIC values between 0.06 – 0.25 mg/mL. Moderate activity was observed for the extracts against the bacteria tested, except for Klebsiella pneumoniae, where noteworthy activity (MIC value of 0.13 mg/mL) was found for the n-butanol fraction. A cidal effect on C. glabrata was recorded by the n-butanol fraction at 1xMIC (0.13 mg/mL) after 30 min of contact time and after 60 min at 1/2xMIC which is better than the positive control (Nystatin) where the cidal effect was only recorded after 4 h of contact time at 0.13 mg/mL. The hexane fraction was subjected to chemical analysis (gas chromatography-mass spectrometry) because of the noteworthy anticandidal activity. Nineteen compounds were identified with major compounds including methyl linolenate (33.31 %), n-hexadecanoic acid (21.32 %), phytol (21.35 %), and octadecenoic acid methyl ester (4.87 %). Leonotis ocymifolia has demonstrated promising antimicrobial properties, particularly against Candida species where the cidal effects link to the possible traditional use for Candida-acquired skin infections. The findings of this study, as determined by the brine shrimp lethality assay, indicate that usage of this plant extract poses minimal risk.