Exploring ethnomedicinal approaches in combating infectious tuberculosis: A South African alternative

Tuberculosis (TB) has become a global health crisis, affecting one-third of the global population. It is characterized as a highly infectious disease due to Mycobacterium tuberculosis infection. According to the World Health Organization, TB causes 1.5 million fatalities worldwide per year. Moreover, persistent TB infection in patients with human immunodeficiency virus is responsible for countless deaths and has become a major player in antimicrobial resistance. Despite TB management strategies, multidrug-resistant TB has dramatically increased and anti-TB drugs have become highly toxic and less effective. Studies have validated the scientific importance of traditional African practices in treating infectious diseases. As a result, the global population is gravitating toward a more natural and eco-friendly approach. Hence, there is a growing interest in using medicinal plants as natural alternatives to conventional antimicrobial drugs. No wonder 80% of the global population depends on medicinal plants for primary healthcare. Southern Africa is considered an unexplored “Garden of Eden” for the discovery of novel biocompounds for pharmaceutical applications. Several commercial natural products have southern African origins, which gained international recognition. Furthermore, medicinal plants have been reported to possess several antibacterial, anti-inflammatory, anticancer, antifungal, antioxidant activities as well as other useful bioactivities. Hence, this review paper highlights some Southern Africa indigenous medicinal plants with anti-TB. We further drive in the traditional uses as well as the phytochemical compounds. The review inspires advanced research on the endless possibilities of the medicinal plant as a promising anti-TB alternative.


INTRODUCTION
Southern Africa is recognized for its rich and remarkable floral diversity, with nearly 22,755 plant species.Besides, approximately 3,000 plant species are used to treat numerous diseases (Neffati et al., 2017;Twilley et al., 2020;Van Wyk and Prinsloo, 2018).Since the beginning of time, humankind has been utilizing plants for their basic requirements, such as clothing, food, shelter, flavors, fertilizers, and fragrances (Jain et al., 2019).Furthermore, traditionally the indigenous people of South Africa have consumed medicinal plants to cure infectious diseases and treat ailments throughout history (Oguntibeju, 2018).Street et al. (2008) have estimated that almost 52% of the South African population, which accounts for nearly 27 million, relies on native medicinal plants for their essential healthcare treatments.
In light of the above, African traditional medicine (ATM) has been part and parcel of the legislative framework of South Africa (Gqaleni et al., 2007).This is because traditional medicine and practices have played an integral role in the nation's history and plant knowledge has been passed down from generation to generation.Furthermore, the use of traditional medicine has exploded because of its easy accessibility, affordability, and considerable tribal knowledge (Semenya et al., 2012).Various scientific reports have supported the claims made by traditional healers about the countless biological properties of plants, including their antiviral, antibacterial, antioxidant and antiinflammatory, immunomodulatory, and anticancer activities (Kshirsagar and Rao, 2021;Reddy et al., 2020).Tuyiringire et al. (2020) have shown increasing evidence of medicinal plants as a natural source of anti-tuberculosis (TB) agents.Their study further highlighted that the selected candidates could combat multidrugresistant (MDR) TB (Tuyiringire et al., 2020).
South Africa is among the eight countries with the highest TB burden worldwide.TB is now the second most infectious disease due to the high number of fatalities worldwide, surpassing the human immunodeficiency virus (HIV).TB is caused by infectious Mycobacterium tuberculosis that usually affects the lungs (Berkowitz et al., 2018).In 2018, approximately 1.5 million individuals died from TB, 10.0 million patients became sick from TB, and nearly 1.7 billion people suffered from M. tuberculosis infection worldwide (Padmapriyadarsini et al., 2021).Moreover, persistent TB infection in patients with HIV is responsible for countless fatalities and has become a major driver of antimicrobial resistance.The current TB treatment has displayed numerous challenges, including expensive drug therapy, its ineffectiveness since the development of drug resistance, and the counteractions of HIV infection.
Moreover, combination therapy causes serious symptoms and high toxicity levels (Anochie et al., 2018).Regarding the current antibiotic therapy, failure is inevitable.Well-documented studies are available on the various biological activities and numerous secondary biocompounds (e.g., polyphenols, flavonoids, and alkaloids) of traditional medicinal plants (Chiocchio et al., 2021;Oguntibeju, 2018;Street et al., 2008).On the other hand, South Africa has an abundant wealth of traditional medicinal plants with tremendous anti-TB properties (Anochie et al., 2018;Madikizela and McGaw, 2017).Hence, untapped alternatives in the drug discovery and development process must be explored to uncover new cost-effective, accessible, more potent, and less toxic natural plant-based drugs.In conclusion, these medicinal plants might be explored for therapeutic prevention, control, management, and treatment of TB.

METHODOLOGY FRAMEWORK
In the present review, we searched online databases such as Google Scholar, ScienceDirect, Scopus, and Web of Science to screen and select research papers.Terminologies including biocompounds, TB, medicinal plants, and South Africa alone or in combination were used to search the electronic databases for research papers.

Artemisia afra Jacq. Ex Willd. (African wormwood)
Tradition uses of the African wormwood plant Artemisia afra Jacq.Ex Willd. is a native aromatic plant distributed in the southern locations of Africa, including South Africa, Zimbabwe, and Namibia; thus, it flourishes in the Gauteng and Limpopo areas of South Africa.The Zulu people named the plant "Mhlonyane," Xhosa "Umhlonyane," Sotho "Lanyana," Afrikaans "Wildeals," and Tswana "Lengana," and English speakers refer to the plant as "African wormwood" (Fig. 1) (Liu et al., 2009).Moreover, traditional use of the plant involves the treatment of coughs, fever, headaches, chills, indigestion, loss of appetite, gastric disorders, colic, croup, gout, whooping cough, asthma, diabetes, malaria, bladder, influenza, kidney disorders, heart inflammation, purgative, convulsions, and rheumatism.Various scientific studies have supported the traditional claims that African wormwood showed promising antiviral, antiinflammatory, and antibacterial activities.In rural areas in the Eastern Cape Province of South Africa, people treat diabetes by infusing the leaves or roots of African wormwood "Umhlonyane" (Kshirsagar and Rao, 2021).Others boil the leaves to cure respiratory infections and inhale the vapor to cure menstrual chill.A tea preparation of African wormwood sweetened with honey is also used for therapeutic purposes.For this, an increasing number of people are becoming more interested in African wormwood due to its infinite possibilities.Artemisia afra "African wormwood" is currently one of the most talked-about medicinal plants in South Africa (Du Toit and Van der Kooy, 2019).

Anti-TB properties of the African wormwood plant
Various studies have reported African wormwood as a potent medicinal plant with superior bioactivities (Kshirsagar and Rao, 2021).A recent study determined that the minimum inhibitory concentrations (MICs) of Artemisia annua and A. afra extracts against Mycobacteroides abscessus and M. tuberculosis showed excellent bactericidal activity against M. tuberculosis.The results further showed that African wormwood exhibited potent anti-TB effects.These strains have been reported to be virulent Erdman strains and might be regarded as resistant strains, hence acting as chemotherapeutic agents against infectious M. tuberculosis (Martini et al., 2020).According to Ntutela et al. (2009), the dichloromethane extract of African wormwood inhibited the bacterial replication of Mycolicibacterium aurum.The actions ensured that the drug copying was entirely stopped.This was due to the invasion of the heme molecule that affects the reduced oxygen for the survival of the pathogen (Ntutela et al., 2009).Several studies have established that African wormwood might be a suitable candidate as an anti-TB agent (Gemechu et al., 2013;More et al., 2012).Mativandlela et al. (2008) determined antimycobacterial activity using the MIC of A. afra extracts against Mycobacterium smegmatis and M. tuberculosis.The results showed that A. afra exhibited some anti-TB activity and could be a good candidate for treating TB and TB-related symptoms (Mativandlela et al., 2008).
Three local medicinal plants commonly used for the treatment of TB in the Eastern Cape Province, South Africa, were screened using a twofold microdilution bioassay.The A. afra dichloromethane and ethanol extracts showed good anti-TB activity against M. aurum A+.Further analysis also indicated that A. afra extracts inhibited the growth of Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, and Bacillus cereus (Buwa and Afolayan, 2009).Interestingly, a survey study was conducted on 52 Bapedi traditional healers in the districts of Limpopo, South Africa.The results indicated that A. afra was the most widely used medicinal plant in treating and managing TB in the Limpopo province of South Africa (Semenya and Maroyi, 2013).Despite the extensive biological activities of A. afra, several studies have demonstrated that A. afra extracts and their volatile oils possess some toxicological effects (Kane et al., 2019;Mongalo et al., 2020;Mukinda and Syce, 2007;Mungho et al., 2018;Sunmonu and Afolayan, 2013).

Ziziphus mucronate Willd. (the buffalo thorn)
Tradition uses of the buffalo thorn plant Ziziphus mucronata Willd. is a deciduous native sub-Saharan Africa plant, growing from South Africa northwards to Eritrea and Ethiopia.Historians believe that Christ's crown was made from the Ziziphus spina-christi Willd.plant, which closely resembles Z. mucronata.Ziziphus mucronata is commonly known as buffalo thorn due to its pointed leaves.Moreover, in Latin, "ziziphus" means thorn, and "mucronata" refers to pointed leaves.Various plant parts of Z. mucronata are used traditionally to treat several ailments, such as gastrointestinal conditions, rheumatism, and snake bites.The bark infusions help relieve cough, body pains, respiratory conditions, and chest issues.For the treatment of gonorrhea, diarrhea, and dysentery, indigenous people use Z. mucronata root drinks (Mekonen et al., 2020; Fig. 2).

Anti-TB properties of the buffalo thorn plant
An in-depth study was conducted on the ATM system for treating TB using medicinal plants.The study highlighted various herbal plants producing secondary biocompounds as potential anti-TB agents and Z. mucronata plant was listed (Anochie et al., 2018).Indigenous people of the South African tribes used medicinal plants to combat TB (Dzoyem et al., 2016;Green et al., 2010;Sharifi-Rad et al., 2020).Moreover, Sigidi et al. (2016) reported that Z. mucronata extracts exhibited some anti-TB activity at concentrations >500 μg/ml against the M. tuberculosis H37 strain.Another research study demonstrated that Z. mucronata extracts produced cyclopeptide alkaloids, which were well-known to exhibit significant anti-TB effects against M. tuberculosis (Lomchoey, 2014).The Mycobacterium species have structural cell wall functions to withstand the habitat and anti-TB agents and survive adverse environmental conditions for countless years.This has led to the ever-increasing MDR and extensively drug-resistant genes, which make the treatment of TB challenging (Mongalo et al., 2020).

Knowltonia vesicatoria (brandblaar)
Tradition uses of the brandblaar plant Knowltonia vesicatoria is a slow-growing perennial fynbos indigenous South African plant that is widely distributed in the Cape Peninsula stretching to Grahamstown.Furthermore, K. vesicatoria is referred to as "brandblaar" by the Afrikaans people of South Africa.It has been popular in South Africa since European colonization due to its wide range of beneficial uses.The native tribes used K. vesicatoria leaves to soothe aching backs and joints.Moreover, it was used to treat colds, arthritis, rheumatism, flu, and, sometimes, toothache (van Wyk and Gericke, 2000; Fig. 3).

Anti-TB properties of brandblaar plant
In line with the above, another study revealed that K. vesicatoria (aerial parts) extracts demonstrated the best bioactive activities against M. tuberculosis with inhibition of MIC of 39.06 μg/ml.In contrast, the extracts showed weak bioactivity against nonpathogenic M. smegmatis.Moreover, Labuschagné et al. (2012) showed that K. vesicatoria extract possessed strong anti-TB properties against drug-resistant M. tuberculosis isolates and exhibited a MIC value of 50.00 μg/ml.The combination effect of K. vesicatoria extract with other compounds reduces the MIC value (Labuschagné et al., 2012).Regardless of the limited data, various researchers have advocated for using K. vesicatoria as a substitute for commercialized anti-TB agents (Anochie et al., 2018;Babiaka et al., 2015;Martolia et al., 2020;Nielsen et al., 2012).Despite the limited studies, several studies supported the anti-TB effects of K. vesicatoria based on in vitro laboratory-based reports (Krige et al., 2009;Kuete et al., 2021;Labuschagné et al., 2008;Nielsen et al., 2012;Rawat et al., 2021).

Phytochemical compounds isolated from the fever tea plant
Lippia javanica is rich in biocompounds and essential oils, such as pipertenone, tagetenone, ipsdienone, p-cymene, ipsenone, myrcene, linalool, carvone, sabinene, ocimenone, limonene, caryophyllene, and myrcenone (Shikanga et al., 2010).It has been revealed that piperitenone extracted from L. javanica could inhibit the growth of E. coli and Bacillus subtilis at a dilution rate of 1% (Manenzhe et al., 2004).It can also inhibit the growth of Acinetobacter calcoaceticus, Salmonella typhi, S. aureus, and Micrococcus kristinae with a MIC range of 12-50 μg/ml, using kanamycin and dimethyl sulphoxide as control (Samie et al., 2009).The same was observed in the leaf extract (acetone, methanol, and hexane extract) of L. javanica against 15 bacterial species with a MIC range of 1.5 to >12 mg/ml (Nyahangare et al., 2012).Biocompounds such as lippialactone derived from ethyl acetate extract of the aerial parts of L. javanica, according to Ludere et al. (2013), prevent the growth of E. coli and S. aureus at 10 mg/ml.Apigenin, a phenolic compound, which is a well-known antibacterial agent, is also extracted from L. javanica and has an antibacterial effect on Vibrio cholera, Enterococcus faecalis, S. typhi, Proteus mirabilis, and Pseudomonas aeruginosa (Cushnie and Lamb, 2005;Martini et al., 2004;Shikanga et al., 2010).Isoverbascoside and verbascoside were extracted from the leaf of L. javanica and can exhibit antifungal activities against mycelia at above 0.6 mg/ml −1 (Lima et al., 2003).

Anti-TB properties of the fever tea plant
Mujovo et al. (2008) reported that among all the compounds isolated from L. javanica, only euscaphic acid, which is a triterpenoid carboxylic acid, showed antimycobacterial activity when tested against a drug-sensitive strain of M. tuberculosis with a MIC of 50 μg/ml.Acetone leaf extract of L. javanica showed antimycobacterial activity against M. smegmatis with the lowest MIC value of 0.47 mg/ml (Masoko and Nxumalo, 2013).These compounds with antimycobacterial activities extracted from L. javanica have passed through preliminary evaluations and have turned out to be very effective.Thus, they can be used to produce new and more effective drugs for the treatment of TB (Maroyi, 2017;Masoko and Nxumalo, 2013;Mujovo et al., 2008).Lippia javanica is regarded as one of the most commonly used medicinal plants by Bapedi traditional healers to cure TB infection in the Limpopo province of South Africa (Semenya and Maroyi, 2013).

Anti-TB properties of the Natal guarri plant
Most of the compounds isolated from E. natalensis exhibited inhibitory activities against Mycobacterium species.Using a radiometric respiratory BACTEC assay, Lall and Meyer (2001) observed a MIC value of 100 μg/ml while evaluating the antimycobacterial activities of both drug-sensitive and drugresistant strains of M. tuberculosis.Evaluating the antimycobacterial activities of crude extract, diospyrin, and 7-methyljuglone, isolated from the root of E. natalensis, against M. tuberculosis produced MIC values of 8.0, 8.0, and 0.5 μm/ml, respectively (Lall and Meyer, 2005).Furthermore, 7-methyljuglone and diospyrin are the most bioactive and antimycobacterial compounds isolated from E. natalensis based on all evaluations and previous studies (Mahapatra et al., 2007;Maroyi, 2017;Lall;2001;van der Kooy, 2004;van der Kooy, 2007).
A previous study by Bapela et al. (2008) revealed that naphthoquinone, 7-methyljuglone was the lead bioactive compound in E. natalensis extracts.The data showed that E. natalensis extracts were potent against M. tuberculosis and M. smegmatis.In another study, naphthoquinone, 7-methyljuglone was also isolated from the acetone extract of E. natalensis and showed a good inhibitory effect against Mycobacterium bovis (MIC = 26 μg/ml), compared to M. smegmatis and Mycobacterium fortuitum.Even though the strains were nonpathogenic, they were used as prototypes to identify the potency of plant-based extracts (McGaw et al., 2008).Furthermore, E. natalensis has been shown to be a potent antimycobacterial candidate in the literature; however, more research is warranted as the studies in this area are limited.

Immune adjuvant effect of medicinal plants against infectious TB
Biological therapy, often known as immunotherapy, is a type of treatment that uses the body's natural immune system to protect against infection, cancer, and other disorders and mitigate the effects of other treatments.Biological response modifiers (BRMs), which include vaccinations, monoclonal antibodies, cytokines, and adjuvants, are used in biotherapy.BRMs can be utilized individually or in combination (Kuroki et al., 2012).Immunomodulatory activities have been discovered in medicinal plants typically used as herbal medications.Both nonspecific and specific immunity may be stimulated by these substances.These plants may promote both humoral and cell-mediated immunity, or simply one of them, while reducing the immune system's cellmediated component (Rao et al., 1994).
Immunomodulatory therapy may be a viable alternative to traditional chemotherapy for a variety of diseases, particularly when the host's defense mechanisms must be activated in the face of impaired immune responsiveness or when selective immunosuppression is required in situations such as inflammatory diseases, autoimmunity, and organ/bone marrow transplantation (John et al., 2022).Numerous polysaccharides derived from TCM plants have recently been discovered to be biocompatible, biodegradable, and immunomodulatory, indicating that they could be used as vaccine adjuvant options (Khademi et al., 2018;Wan et al., 2022).Due to the lack of innate immune stimulation, conventional vaccinations have been proven to be insufficiently immunogenic.As a result, adjuvants for new-generation vaccines must ensure that the vaccine closely resembles illness in order to elicit a strong immune response.While adjuvants are powerful immunostimulators, most of them are not approved for use in the clinic due to unfavorable side effects.As a result, a substantial study focused on identifying the active components of adjuvants and then modifying them to reduce adverse effects (Song and Hu, 2009).
In a 2020 study, Roy et al. (2020) discussed the possible use of phytochemical-derived efflux pump inhibitors and immunotherapy to combat TB and provided a brief look at the molecular mechanism and structure of drug-efflux pumps seen in MTB.A recent article on monoclonal antibodies against antigens of Mycobacterium TB has produced mixed results.It showed that phagocytic cells enhanced antibody-mediated phagocytosis of mycobacteria by phagocytic cells using sera from patients vaccinated with bacillus Calmette-Guérin.Furthermore, cytokines and inhibitors as immunomodulators were examined in a clinical trial involving 50 patients with MDR-TB, where adjunct supplementation with recombinant human IL-2 for 7 months resulted in increased sputum smear conversion and improved immune status (Gupta et al., 2016).
Immunoxel (Dzherelo) is a water-alcohol extract of medicinal plants used in Ukraine as a TB and HIV immunotherapy adjuvant.Patients exhibited faster defervescence, weight increase, higher hemoglobin content, and less inflammation, as shown by the lower leukocyte counts and erythrocyte sedimentation rate.Only 19% of the individuals in the placebo group converted.These data suggest that solid Immunoxel delivered through the mucosa is equal to the original liquid Immunoxel given twice daily for 2-4 months (Efremenko et al., 2012).In a recent study, patients were divided into two groups: the first (n = 137) received a sublingual honey lozenge formulated with the botanical immunomodulator Immunoxel once daily; the second (n = 132) was given placebo lozenges in addition to conventional ATT.Immunoxel's sputum clearing was effective in all types of TB.
Immunoxel reduced TB-related inflammation, as shown by the decreased defervescence and normalization of high leukocyte counts and erythrocyte sedimentation rate.There were no adverse side effects observed at any period.Immunoxel is a commercially accessible immunotherapeutic intervention that is cost-efficient, safe, and successful in treating TB (Batbold et al., 2017).
In the in vitro and aerosol mouse models of MTB infection, researchers looked at the immunomodulatory effects of G1-4A, a polysaccharide extracted from the Indian medicinal plant Tinospora cordifolia.The findings showed that modulating host immune responses with G1-4A could increase the therapeutic efficacy of existing anti-tubercular medicines and could be a promising technique for developing new TB treatments (Gupta et al., 2016).Isoniazid as a potential hostdirected therapy when used with luteolin, a plant-derived hepatoprotective immunomodulator, enhances anti-TB immunity, decreases the period of TB treatment, and avoids disease relapse.Luteolin also promotes central memory T-cell responses, which improves long-term anti-TB immunity.We also discovered that luteolin boosts the activity of natural killer and natural killer T-cells, both of which have antitubercular properties (Singh et al., 2021).Indigenous people of South Africa have relied on medicinal plants for their anti-TB healing properties.In the current review, it can be further deduced that plant-based biocompounds exhibit excellent therapeutic properties and are thus suitable candidates for treating TB, especially multiresistant M. tuberculosis strains.These findings should encourage researchers to pursue such TB management treatments in order to discover novel, costeffective, efficacious, and sustainable drugs that can inhibit the growth and proliferation of M. tuberculosis and reduce the fatality rate of TB, even in patients with HIV in South Africa and beyond.They also shed light on the importance of South African medicinal plants and the need for more in-depth studies, including clinical studies in TB management.
Using tetrazolium microplate assay, Green et al.(2010)   observed that acetone leaf extract of B. micrantha was more active against M. tuberculosis with a MIC value of 25 μg/ml than other extracts (methanol, hexane, and ethanol).Moreover, Green et al. (2011) used a resazurin microplate assay to evaluate the antimycobacterial activity of n-hexane fraction, a subfraction of ethyl acetate fraction of the acetone stem extract of B. micrantha against M. tuberculosis.They observed 20% and 35% inhibition in the growth of M. tuberculosis H37Ra and M. tuberculosis that is resistant to all first-line drugs at 10 μg/ml.The primary ethyl acetate fraction inhibited the growth of M. tuberculosis resistant to streptomycin, rifampicin, isoniazid, and ethambutol at 50 μg/ml.The evaluations from researchers(Akinyeye and  Olatunya, 2014;Green et al., 2010; van der Kooy, 2007)  can serve as scientific validations for producing more effective and efficient drugs for the treatment of TB.Numerous biocompounds with abundant biological activities have been isolated from B.