Antioxidant, antimicrobial, safety profiles and phytochemical analysis of selected medicinal plants collected from northern Kwazulu-Natal, South Africa

The antimicrobial resistance (AMR) of many microorganisms to conventional antibiotics poses a serious threat to human health. Although medicinal plants are preferred as source of therapeutic potential, the toxicity of such plants remains less studied. The objective of the study is to assess the antimicrobial, antioxidant, cytotoxicity, and phytochemical components of the selected medicinal plants’ extracts. The microdilution broth assay was used to evaluate the antimicrobial activity of both aqueous and the organic extracts against animal and human-infecting pathogens. Cytotoxicity of the extracts was evaluated against human dermal fibroblast cell line while heavy metal analysis was carried out using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Additionally, 2,2-Diphenyl-1-Picrylhydrazyl (DPPH), 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), and possible iron chelation were used to measure the extracts’ antioxidant activity. Gas chromatography time-of-flight mass spectrometry (GC-T O F-MS) was used to evaluate the phytochemical analysis. Aqueous extract from Bauhinia galpinii yielded the notable lowest minimum inhibitory concentration (MIC) of 0.05 mg/ml against both Proteus vulgaris and Cryptococcus neoformans . The organic extracts from the selected medicinal plants exhibited some varying degrees of cytotoxicity towards the human dermal fibroblast (HDF) cell line. The extracts further exhibited a better inhibition of iron than 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS). In the heavy metal and essential elements analysis, the strongest positive correlation was obtained between zinc and cadmium (0.969524), followed by chromium and strontium (0,909772). The organic extracts from both Milletia grandis and Bauhinia galpinii contained compounds such as Hexadecanoic acid, Toluene, Tetradecane, Hexadecane, Indole and Pentadecane with lower percentage areas. The organic extracts from B. galpinii contained Pyrrole (27.131%), 3-Tosyl sedoheptulose (5.826%), while Milletia grandis contained 4-(4-tert-Butylphenyl)-1, 3-thiazol-2-ylamine (1.974%), and 2-Pentadecanone, 6, 10, 14-trimethyl- (1.692%) as compounds with higher % area. The extracts from the selected medicinal plants exhibited potent antimicrobial and antioxidant activity and could well be used as complementary and alternative medicine. However, it is concerning that the plant materials from the selected plants contained some minor quantities of heavy metals, although less than the stipulated quantities by World Health Organisation (WHO).