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The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family
Thesis (PhD (Paraclinical Sciences))--University of Pretoria, 2015.
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2026
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| access_status_str | Open Access |
| author2 | McGaw, Lyndy Joy |
| author_browse | McGaw, Lyndy Joy |
| author_facet | McGaw, Lyndy Joy |
| collection | Thesis |
| description | Thesis (PhD (Paraclinical Sciences))--University of Pretoria, 2015. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/110076 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:36:29.578Z |
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| publishDate | 2026 |
| publishDateRange | 2026 |
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| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/110076 The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family McGaw, Lyndy Joy aroabimbola@yahoo.co.uk Eloff, Jacobus Nicolaas Aro, Abimbola O. Antimycobacterial Synergy Immune modulatory Tubercolosis Thesis (PhD (Paraclinical Sciences))--University of Pretoria, 2015. Tuberculosis, a contagious disease caused by Mycobacterium tuberculosis, has become a global health problem. One-third of the world‘s population is latently infected with the pathogen and one in ten develop active disease in their lifetime. Due to population growth, the incidence of TB is increasing annually , thereby resulting in a continued health crisis and financial burden in various parts of the world, especially Asia and Africa. Current TB chemotherapy is generally effective, but the disease is a global challenge due to infections concurrent with the pandemic of HIV/AIDS and the emergence of drug resistant strains. There is a need to identify novel anti-TB drugs. In recent years the use of and search for drugs derived from plants have been on the increase but evaluating the biological activities of these plants is necessary to rationalise their use by communities, and also to discover possible lead compounds. The Rubiaceae family has played a significant role in drug discovery by providing molecules used as templates for the development of drugs such as quinine isolated from Cinchona species used in the treatment of malaria. For this study, 15 species belonging to the Rubiaceae family were selected for evaluation following initial determination of activity against Mycobacterium smegmatis in a broad screening procedure of the Phytomedicine Programme . The species are: Cephalanthus natalensis Oliv., Cremaspora triflora (Thonn.) K.Schum., Feretia aeruginescens Stapf, Hymenodictyon parvifolium Oliv, Hyperacanthus sp. E.Mey. ex. Bridson, Keetia gueinzii (Sond.) Bridson, Keetia sp. E.Phillips, Kraussia floribunda Harv., Mussaenda arcuata Poir., Oxyanthus speciosus DC., Pavetta lanceolata Eckl., Pavetta schumanniana F.Hoffm. ex K.Schum., Psychotria capensis (Eckl.) Vatke, Psychotria zombamontana (Kuntze) E.M.A.Petit and Vangueria infausta Burch. The acetone extracts of the selected plants were screened against three non-tuberculous mycobacteria (NTM): M. smegmatis (ATCC 1441), M. aurum (NCTC 10437) and M. bovis BCG (Pasteur strain P1172) as well as against a pathogenic M. tuberculosis field strain (TB 8104) using a two-fold microdilution assay to determine their antimycobacterial activity. Another objective of this study was to compare activities of the extracts against different Mycobacterium species to determine which non-pathogenic Mycobacterium species correlates best to the pathogenic M. tuberculosis in terms of susceptibility to the plant extracts. The extracts of P. zombamontana, C. natalensis and Keetia sp. had the best MIC value of 0.04 mg/mL followed by O. speciosus and P. capensis (0.06 mg/mL). The acetone extracts of M. arcuata and Keetia sp. had weak activity against the non-pathogenic M. bovis BCG with MIC values of 1.56 mg/mL and 1.41 mg/mL respectively. Of all the fifteen screened plant species, F. aeruginescens had the highest percentage yield of 11.32% while the lowest yield was obtained from Vangueria infausta (0.96%). The total activity was calculated as mass (mg) divided by MIC (mg/ml). P. zombamontana acetone extract had the highest total activity of 1 077 mL/g against M. smegmatis while the extract of O. speciosus was the second best with values of 511 mL/g and 438 mL/g against M. aurum and M. bovis BCG respectively. Activity against M. aurum was the best predictor of activity against pathogenic M. tuberculosis (correlation coefficient= 0.9) supporting published studies, and was closely followed by M. bovis xv BCG (correlation coefficient= 0.8). The acetone extract of O. speciosus contained the highest number of chemical constituents active against the tested mycobacteria (9) based on the bioautography results, while V. infausta had the lowest number (2). The cytotoxicity assessment was done using the tetrazolium-based MTT colorimetric method and the selectivity index (SI) values were calculated by dividing the LC50 (mg/mL) by the MIC (mg/mL) to determine if the antimycobacterial activity observed was due to selective activity rather than a general metabolic toxin. The crude extract of V. infausta had the highest LC50 value (lowest toxicity) of 0.76 mg/mL while the extract of P. capensis was the most toxic (LC50 = 0.015 mg/mL) against C3A liver cells. The extracts of P. capensis (0.034 mg/mL), P. zombamontana (0.032 mg/mL) and H. parvifolium (0.037 mg/mL) exhibited some degree of cytotoxicity against Vero kidney cells. The average SI value for all the crude extracts ranged from 1.5-1.7 and 0.7-0.9 for C3A liver cells and Vero kidney cells respectively. The extract of O. speciosus had the best SI values for C3A cells (4.91, 6.55 and 5.62 respectively against M. smegmatis, M. aurum and M. bovis BCG). Oxyanthus speciosus had the highest SI values of 2.60, 3.47 and 2.97 against M. smegmatis, M. aurum and M. bovis BCG for Vero kidney cells. Based on the preliminary screening, six plant species had good antimycobacterial activity (C. natalensis, C. triflora, O. speciosus, P. capensis, P. lanceolata and P. zombamonatana) and were selected for further studies. The checkerboard method was used to determine the synergistic antimycobacterial activity of the extracts in combination with a known anti-TB drug, rifampicin. The acetone extracts of these six plants, each in combination with rifampicin, was tested against M. smegmatis, M. aurum and M. tuberculosis field strain (TB 8104). Cremaspora triflora extracts produced the best synergistic effect with _FIC of 0.008 while the acetone extract of Oxyanthus speciosus had a non-interactive effect (_FIC=2) against Mycobacterium aurum. The DPPH assay was used to determine the quantitative antioxidant activity of these extracts and the number of antioxidant compounds in a qualitative DPPH assay. Inhibition of nitric oxide (NO) release from mouse macrophage cells (RAW 264.7) was measured using the Griess reagent to determine potential anti-inflammatory activity. Plants as natural antioxidants can play a significant role in the inhibition of NO production. Extracts of P. zombamontana and P. capensis had good antioxidant activity with IC50 values of 1.77 ± 0.13 and 2.94 ± 0.33 respectively when compared to trolox and ascorbic acid (5.67 ± 0.24, 4.66 ± 0.25). All the extracts tested inhibited nitric oxide (NO) production in a dose dependent manner in LPS-stimulated RAW 264.7 macrophages. The extracts all had relatively low cytotoxicity against the tested cell except the acetone extract of Psychortia capensis having relative cytotoxicity. To determine the immuno modulatory effect of active extracts, human macrophages (U937 cells) were exposed to the most active extracts and the TH1/TH2 cytokine release was quantified using flow cytometry. The cytokine profiles for the LPS-stimulated U937 human macrophage cell line revealed a mixed TH1/TH2 response. Hence, the five screened plant extracts possess varying degrees of immune modulatory effect. xvi The activity against mycobacteria in an intracellular environment was determined using a model of M. fortuitum infecting the mouse macrophage (RAW 264.7) cell line. The crude extract of O. speciosus significantly decreased the number of intracellular mycobacteria at 0.5, 1, 2 and 4 times the MIC value, revealing some degree of bactericidal activity in a dose and time-dependent manner compared with rifampicin. This study also validates the use of non-pathogenic mycobacteria for intracellular study. Finally, the crude extract of Oxyanthus speciosus was fractionated and two bioactive compounds were isolated using open column chromatography and bioassay-guided fractionation. Fractionation did not increase the antimycobacterial activity of the crude extract against the tested organisms but rather revealed a strong evidence of synergism. A carotenoid (lutein) and ursene-type triterpene (rotundic acid) were isolated from the acetone extract of O. speciosus and both had a moderate antimycobacterial activity (MIC = 12.5 µg/ml -100 µg/ml) against three non-pathogenic and one pathogenic mycobacteria. The two isolated compounds were not toxic at the highest tested concentration (200 µg/ml) and also inhibited nitric oxide production by RAW 264.7 macrophage cell l Paraclinical Sciences PhD (Paraclinical Sciences) 2026-05-15T17:26:14Z 2026-05-15T17:26:14Z 16/02/10 2015 Thesis http://hdl.handle.net/2263/110076 en application/pdf |
| spellingShingle | Antimycobacterial Synergy Immune modulatory Tubercolosis The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title | The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title_full | The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title_fullStr | The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title_full_unstemmed | The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title_short | The antimycobacterial and immune modulatory activity of fifteen South African plant species in the Rubiaceae family |
| title_sort | antimycobacterial and immune modulatory activity of fifteen south african plant species in the rubiaceae family |
| topic | Antimycobacterial Synergy Immune modulatory Tubercolosis |
| url | http://hdl.handle.net/2263/110076 |