Traditional or herbal medicines, derived from plant sources, are generally considered safe at traditional dosages due to their historical usage in various cultures. These plants are the most abundant natural sources of active drugs and play a vital role in the ethnomedical treatment of a wide range of ailments, primarily due to their diverse phytochemicals responsible for biological activities.
The World Health Organization defines traditional medicine as the total of the knowledge, skills, and practices based on the theories, beliefs, and experiences indigenous to different cultures, used in maintaining health and treating physical and mental illnesses. In Nigeria, as in other African nations, traditional and complementary medicine continues to thrive.
Most plants used in ethnomedicine have been documented for their promising activities against multiple disease-causing microorganisms. Research efforts are accelerating to better understand medicinal plants, providing models for about 25–50% of marketed drugs. The antimicrobial activities of these useful plants vary, with many acting in synergy to reduce the side effects of synthetic drugs, while others function as quorum quenchers.
A study published in the Scientific World Journal revealed that some plants in Nigeria possess antimicrobial properties. These plants were classified based on the groups of organisms they are effective against, highlighting their potential in treating infectious diseases.
Plants with Antibacterial Properties
- Terminalia glaucescens – The Root and leaf extracts were investigated for antimicrobial activity against E. coli and S. typhi and it was effective against E. coli and Salmonella typhi.
- Azadirachta indica (Neem) – The Acetone and ethanol extracts of the tree bark bark were tested for antibacterial activity against multidrug-resistant Salmonella typhi strains. it was found to be effective against multidrug-resistant Salmonella typhi.
- Zingiber officinale (Ginger) and Allium sativum (Garlic) – An aqueous and ethanolic extracts of Zingiber officinale and Allium sativum were investigated for their effects on foodborne pathogens such as Salmonella species and E. coli. Different sensitivity profiles observed against various pathogens and it was effective against various foodborne pathogens like Salmonella species, Bacillus cereus, E. coli, and S. aureus.
- Diospyros barteri and D. monbuttensis (Ebony trees) leaves – it was potent antibacterial activity against a wide range of Gram-positive and Gram-negative bacteria.
Senna alata (Candelabra bush) flowers – Effective against clinical isolates of S. aureus, C. albicans, E. coli, Proteus vulgaris, P. aeruginosa, and B. subtilis. - Heeria insignis – Possesses antibacterial and antidiarrheal activities.
- Spondias mombin – Outstanding anthelmintic activity.
- Psidium guajava (Guava), Vernonia amygdalina, and traditional Ogi-tutu – V. amygdalina has high ameliorative effects against V. cholerae infection.
- Thymus vulgaris (Thyme) – Antibacterial property on multiple antibiotic-resistant Vibrio fluvialis and Vibrio parahaemolyticus.
- Argemone mexicana L. – Inhibited B. subtilis and K. pneumoniae.
- Annona senegalensis – Potent antibacterial activity and antidiarrheal properties.
- Ficus exasperata – The leaves inhibited the growth of Gram-positive organisms.
Plants with Antimalaria Properties
- Diospyros monbuttensis was found to be highly effective against Plasmodium falciparum with in an in vitro sensitivity pattern.
- Momordica charantia exhibited activity against Plasmodium falciparum in an in vitro sensitivity pattern.
- Morinda lucida showed the lowest antiplasmodial activity against Plasmodium falciparum in an in vitro study, and also demonstrated potential anticoccidial effects against Eimeria parasites suggesting its use as an anticoccidial drug for poultry.
- Moringa oleifera seeds’ crude ethanolic extract showed the highest parasite inhibition activity against Plasmodium falciparum in an in vitro study using the cold extraction method.
- Landolphia owariensis methanol fractions demonstrated significant antiplasmodial activity against Plasmodium berghei in early, established, and residual infections in albino mice, due to alkaloids, flavonoids, saponins, and tannins present in the fractions.
- Allamanda cathartica is noted as an antimalarial plant.
- Bixa orellana is noted as an antimalarial plant.
- Alchornea laxiflora root extract showed significant antimalarial activity against Plasmodium berghei infection, and its ethyl acetate fraction showed high activity against chloroquine-sensitive and -resistant strains of Plasmodium falciparum in mice.
- Enantia chlorantha is traditionally used for treating malaria, though high doses may cause severe toxic effects; a study on its acute and subacute toxicity in mice showed a mean lethal dose (LD50) of 0.7 g/kg for ethanolic and 43.65 g/kg for aqueous preparations.
- Cajanus cajan showed antimalarial properties, and the ethyl acetate fraction of its crude methanolic extract identified cajachalcone as a biologically active constituent against the multiresistant strain of Plasmodium falciparum in an in vitro study using chromatographic techniques.
- Azadirachta indica has shown antiplasmodial activity, and an in silico study identified margolonone, nimbinone, and nimbione as compounds that modulate the activity of Plasmodium falciparum heat shock protein 90 (PfHsp90).
- Allophylus africanus extracts reduced parasitemia caused by Plasmodium berghei (NK-65) in mice, with flavonoids, saponins, tannins, and carbohydrates predominant in all parts of the plant.
- Justicia flava yielded new compounds such as hanocokinoside, allotaraxerolide, alloeudesmenol, and alloaminoacetaldehyde, which could help in designing new antimicrobial agents; lignans such as (+) isolariciresinol, helioxanthin, and justicinol were isolated from the leaves, while 8-demethylorosunol and orosunol were identified from the root.
Plants with Antifungal Properties
- Calotropis procera exhibited complete inhibition of Microsporum and Trichophyton species after ten days of inoculation with water extract at different concentrations.
- Spondias mombin crude methanolic extract (bark and leaves) exhibited anticandidal effects with inhibition diameters of 11.00 ± 0.47 mm and 15.00 ± 0.47 mm, respectively, and contains phytochemicals such as terpenoids, alkaloids, glycosides, saponin, and flavonoids.
- Psidium guajava extracts were active against Candida albicans isolates from caries-infected patients.
- Alchornea laxiflora leaf extracts showed antibacterial and antifungal activities due to the presence of flavonoids, alkaloids, saponins, tannins, and reducing sugars.
Plants with Antiviral properties
- Macaranga barteri methanolic leaf extract showed the highest antiviral activity against Echovirus 7 and Echovirus 9.
Ageratum conyzoides leaves extract exhibited antiviral activity against Echovirus 7 and Echovirus 19. - Mondia whitei leaves extract demonstrated antiviral activity against Echovirus 7 and Echovirus 19.
- Rheum palmatum and Rheum officinale extracts, along with their main single isolated constituents’ anthraquinone derivatives, inhibited both HIV-1 reverse transcriptase-associated DNA polymerase (RDDP) and ribonuclease H activities.
- Ancistrocladus korupensis produced michellamine A and B, which showed antiretroviral activities.
- Ancistrocladus congolensis produced michellamine A and B, which demonstrated antiretroviral activities.
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