Antimicrobial properties and phytochemical analysis of medical plants used for the treatment of ear infections

Thesis (M.Sc. (Botany)) -- University of Limpopo, 2023

Ear infections are a major health concern that negatively affects the health and welfare of individuals across the globe. The infection is caused by a wide spectrum of bacterial, fungal, and viral pathogens. Treatments of ear infections involve the use of antimicrobials such as antibiotics, antifungals, and antivirals. However, most microbial pathogens have developed resistance to the available antimicrobial drugs. Hence, the study aimed to identify plant species used in traditional medicine as a remedy for ear infections and investigate their antifungal activities against the selected fungal pathogens (Aspergillus fumigatus and Candida albicans). These fungal pathogens cause ear infections in humans. Eight plant species including Carpobrotus edulis L., Cotyledon orbiculata L., Dichrostachys cinerea (L.) Wight & Arn., Erythrina lysistemon Hutch., Flacourtia indica (Burm. f.) Merr., Psidium guajava L., Ricinus communis L., and Sansevieria hyacinthoides (L.) Druce were selected from the ethnomedicinal plant's database of over 300 medicinal plants used for therapeutic purposes in humans. Fresh and dried leaves of selected plants were extracted with solvents of various polarities such as acetone, hexane, methanol, and water. In the current study, methanol extracted a larger quantity (30.75%) of plant materials followed by acetone (6.5%) from dried leaf extract of C. edulis and P. guajava. Acetone extracted more plant material (8.05%) from fresh leaf extract of C. orbiculata. Acetone was the second-best solvent for extracting a larger quantity of dried leaf materials as compared to other solvents. Thin layer chromatography (TLC) was used to analyse the phyto-constituents of different plant extracts. The TLC plates were developed using different eluent solvent systems such as Benzene: ethanol: ammonia hydroxide (BEA), Chloroform: ethyl acetate: formic acid (CEF) and Ethyl acetate: methanol: water (EMW). The TLC chromatograms were visualized under UV radiation at 360 nm. In TLC chromatograms separated with BEA, chemical components with a similar Rf value of 0.88 were observed in acetone, hexane, and methanol-dried leaf extracts of R. communis and S. hyacinthoides. Surprisingly, TLC chromatograms separated in BEA, dried leaf extracts contained the highest number of phyto-constituents with a total of 73 followed by 30 in CEF and EMW (29). However, in chromatograms of fresh leaf extracts a total of 12 compounds were visible in BEA, followed by 5 compounds in EMW, and 1 in CEF. Therefore, the BEA solvent system was the best eluent for separating compounds. In addition, different bands were observed after spraying the TLC plates with vanillin reagent. Antifungal activities of plant extracts were determined using serial microdilution assay against the selected fungal pathogens (Aspergillus fumigatus and Candida albicans). Noteworthy activities (0.02 mg/ml) against C. albicans were observed from P. guajava acetone extract and S. hyacinthoides acetone fresh leaf extracts. The methanol-dried leaf extract of C. edulis was active against A. fumigatus with MIC of 0.02 mg/ml while fresh leaf extract was active with MIC of 0.31–2.5 mg/ml. The dried leaf water extracts of C. edulis and D. cinerea had an excellent activity of 0.02 mg/ml against A. fumigatus. The bioautography assay was used to determine the number of active components in different plant extracts. Antifungal compounds were visible in dried leaf extracts of P. guajava, R. communis, and S. hyacinthoides. A total of 19 antifungal compounds were observed against A. fumigatus. Dried leaf extracts of P. guajava, R. communis, and S. hyacinthoides had an active component with an Rf value of 0.88 against A. fumigatus. In TLC bioautograms developed in BEA, two active compounds with similar Rf values of 0.20 were visible in acetone and methanol extract of P. guajava against C. albicans. The results of this study support the traditional use of the selected plant species to combat ear infections and related ailments in humans. The crude extracts have the potential to serve as an ototopic. The antifungal compounds also have the potential to be isolated and used in the formulation of ototopical drugs that may help lift the health burden caused by ear infections across the globe.

University of Limpopo and Council for Scientific and Industrial Research Inter-Bursary Support (CSIR-IBS)