Document Type : Short Review Article
1 Department of Chemistry, Federal University Gashua, Yobe State, Nigeria
2 Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria
Treatments of various diseases in pharmacology through herbs have begun a long time ago. Herbal medicines have been in practice since time immemorial, and over 80% of the global population depends on medicinal plants to treat disease. Medicinal plants contain active ingredients for functional therapeutics purposes, such as antimicrobial agents. Examples of those medicinal plants are found in different plant species belonging to different families such as Boraginaceae, Loranthaceae, Urticaceae, Plantaginaceae, Loganiaceae, Lamiaceae, among others. The genus, Strychnos belongs to the family of Loganiaceae and consists of about 200 species. Isolated compounds and antimicrobial of a few species from the Strychnos genus have been reported recently. This review aimed to detail the isolated compounds and antimicrobial efficacy of selected Strychnos species reported within 2014 – 2021. Based on the MIC result, the antimicrobial efficacy indicated that extracts of S. madagacariensis and S. pungens have the highest activity against S. typhi, extract of S. lucida have highest activity against B. cereus and S. pyogenes, extract of S. spinosa showed better activity against K. pneumonia and B. subtilis, extract of S. nux-vomica has highest activity against S. aureus, P. aeruginosa and E. faecalis while extract of S. colubrine exhibited excellent activity against C. perfringens. About thirty compounds belonging to alkaloids, terpenoid, terpene, steroids and other class and their pharmacological properties were reviewed in this study. This is concluded that the Strychnos species under this review contains a wide variety of compounds belonging to different classes of phytochemical, possessing significant antimicrobial activity.
The prevalence of the infectious disease has been documented throughout history, and hence the establishment of a healthcare scheme is critical for the quality of life that everyone desire [1, 2].
Herbal remedies are discovered and made known through the traditional therapeutic system while herbal treatments for many diseases have been used in pharmacology for a long time ago. These techniques are known as folk healing and have been used worldwide [3, 4].
Alternative medicine and traditional medicine is known as herbal medicine, has been used in India since time immemorial, according to reference . Plant-based medications are used by about 80% of the world's population for therapeutic purposes, according to reports by reference . These are incredibly beneficial in primary healthcare, extending from rural areas in developing countries to developed ones where modern medicines are primarily employed.
Due to the presence of active chemicals in medicinal plants, they are regarded as complementary therapeutics and have improved the management of ill-health problems . Many of these active ingredients in plants are known as phytochemicals, and they have been shown to have therapeutic properties such as antidepressant activity , antioxidant activity , antimicrobial activity  and other biological activities.
Antimicrobials derived from plants have a lot of medicinal potentialities as reported by reference . Mohammadi and co-workers  studied the antibacterial activity of silver nanoparticles (AgNps) generated from a mixture of Ferula gumosa, Ferula latisecta, Teucrium polium, and Trachomitum venetum leaves and stem bark extracts. A review of Zirconia Nanoparticles produced from plant extracts for medical uses has been published . Selenium nanoparticles made from plant extracts have been studied for various biological applications . Several researches on the antimicrobial activity of medicinal plant extracts have found that they are effective against microbial infections. Compounds isolated from plants, including the genus Heracleum, have been reported .
Bacterial and fungal diseases significantly influence on public health, and their resistance to antibiotics has prompted increased medical worry . Humans contract bacterial infections from the air, food, water, or living vectors . Despite this, many bacteria organisms in human bodies do not cause disease. Bacterial cellulitis, strep throat, vaginosis, bacterial, syphilis, gonorrhoea, chlamydia, tuberculosis, tetanus, cholera, botulism, and various other infections can all be caused by bacteria that enter human bodies. Ringworm, vaginal yeast infection, thrush, histoplasmosis, aspergillosis, fungus meningitis, are examples of fungi infections .
Strychnos is one of the largest genera in the Loganiaceae family, Linnaeus initially discovered based on Strychnos nux-uomica, a type species, and Strychnos colubrine (Strychnos minor). It is pantropical and has approximately 200 species, classified into three geographical groups: 75 species in Africa, 73 species in America, and 44 species in Asia (including Australia). Strychnos potatorum, which may be found in Asia and Africa, is an exception . As a result, the purpose of this review was to describe the chemical compounds and antimicrobial efficacy of some selected Strychnos species (Strychnos colubrine, Strychnos potatorum, Strychnos nux-vomica, Strychnos lucida, Strychnos Spinosa, Strychnos madagacariensis, Strychnos nigritana, Strychnos johnsonii, Strychnos pungens) reported in recent time.
Figure 1. Structure of various chemical compounds isolated from Strychnos species
- Results and Discussion
2.1 Antimicrobial activity
Scientists have synthesized certain antibacterial drugs that are available on the market. Medicinal plants are said to have a variety of phytocompounds that defend them from pathogens and are thought to be a source for a variety of antimicrobial chemicals .
The antimicrobial activity of nine Strychnos species (S. colubrine, S. nigritana, S. potatorum, S. pungens, S. nux-vomica, S. johnsonii, S. lucida, S. Spinosa, and S. madagacariensis) were investigated. The antimicrobial activity of these plants' extracts were tested against nineteen microbial pathogens, seven of which were gram-positive: Staphylococcus aureus, Clostridium perfringens, Enterococcus faecalis, Methicillin-resistant Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Streptococcus pyogenes, eight of which were gram-negative: Escherichia coli, Providencia stuartii, Pseudomonas aeruginosa, Prevotella intermedia, Salmonella typhi, Shigella dysenteriae, Klebsiella pneumoniae, Acinetobacter baumannii, and four fungi: Aspergillus niger, Aspergillus niger, Aspergillus niger, Aspergillus niger (Table 1).
The methanol fruit pulp extracts of S. spinosa, S. madagacariensis, S. pungens and methanol root bark extract of S. colubrine showed antimicrobial activity against S. typhi with S. madagacariensis, S. pungens been highest with minimum inhibitory concentration of 12.5 mg/mL. The petroleum seed extract of S. nux-vomica and aqueous root bark extract of S. colubrine have no antimicrobial activity against S. typhi while the ethyl acetate extract of S. colubrine exhibits the highest zone of inhibition 13.2 mm at 80 mg/mL [20–22].
The antimicrobial activity of n-hexane stem bark and twig extracts of S. lucida against S. pyogenes and B. cereus was compared to that of methanol fruit pulp extract of S. spinosa, S. madagacariensis and S. pungens. According to the findings, S. lucida has the highest minimum inhibitory concentration of 0.064 and 0.032 mg/mL for B. cereus and S. pyogenes respectively [22, 23]. The methanol fruit pulp extracts of S. spinosa, S. madagacariensis and S. pungens showed antimicrobial activity against K. pneumonia and P. intermedia with S. spinosa having a higher MIC value (12.5 mg/mL) for K. pneumonia and similar MIC values (25.0 mg/mL) for P. intermedia for all three plants .
Based on the MIC values of hexane stem bark and twig extracts of S. lucida, petroleum seed extract of S. nux-vomica, ethyl acetate twig extracts of S. lucida and methanol root bark extract of S. colubrine. the MIC values of indicated that B. subtilis is most susceptibility to the n-hexane stem bark and twig extracts of S. lucida , which have a MIC of 0.032 mg/mL while the petroleum seed extract of S. nux-vomica has no antimicrobial action against B. subtilis [20, 21, 23]
The significant difference was observed on MIC value between ethanol stem bark extract of S. johnsonii, aerial plant part extract of S. nigritana, leaves extract of S. nux-vomica, Petroleum ether extract of seed of S. nux-vomica, methanol, ethyl acetate, aqueous root bark extract of S. colubrine and aqueous, ethanol seed extract of S. potatorum against S. aureus. The results revealed that the leaves extract of S. nux-vomica has the highest MIC of 0.2 mg/mL [21, 24–27]. The methanol root bark extract of S. colubrine exhibited excellent activity against C. perfringens, Ethyl acetate and aqueous extract do not show activity against C. perfringens . S. aureus has been identified as the most common bacteria responsible for various human diseases .
The MIC values of leaves extract of S. nux-vomica against P. aeruginosa and E. faecalis were compared to those of ethanol seed extract of S. potatorum. The leaves extract of S. nux-vomica demonstrated a better MIC result (0.1 mg/mL) for both P. aeruginosa and E. faecalis [24, 26].
The study on antifungal activity of ethanol seed extract of S. nux-vomica was found to be ineffective against the fungal strains: A. niger, A. flavus and C. albicans . Based on the MIC values of leaves extract of S. nux-vomica, petroleum seed extract of S. nux-vomica and ethanol seed extract of S. potatorum. It is indicated that E. coli has the highest susceptibility to the leaves extract of S. nux-vomica with a MIC of 0.1 mg/mL [20, 24, 26]. The leaves extract of S. nux-vomica has similar MIC value for both Methicillin-resistant Staphylococcus aureus and A. baumannii .
2.2 Isolated compounds
Table 2 and Figure 1 show the list and structure of isolated compounds reported in the Strychnos species under investigation. About thirty compounds belonging to alkaloids (10′-Hydroxyusambarensine, Strychnopentamine, Nigritanine, Stryvomicine A, deoxy-isostrychnine-chloromethochloride, β-colubrinechloromethochloride, α-colubrine-chloromethochloride, Strychnine and brucine), Terpenoid (Sarracenin, Linalool, α-Terpineol, Nerol, Geraniol, α-Ionone, β-Ionone, Nerolidol and Phytol), Terpene (α-Terpinene, Limonene, Geranyl acetate and Bicyclogermacrene), Flavonoid (Kaempferol-7 glucoside, 7-Hydroxy coumarin, Quercetin-3-rhamnoside, Kaempferol 3-rutinoside and Rutin), Steroids (b-sitosterol) and others (Eugenol, Heptadecane and Dodecanal) were reviewed in this study.
Isolation of 10′-Hydroxyusambarensine and Strychnopentamine from S. usambarensis was reported by , these compounds belong to the alkaloid group. 10’-Hydroxyusambarensine is potent against two strains of Plasmodium falciparum  while Strychnopentamine is reported to have anticancer properties .
Sarracenin was isolated from S. spinosa by . It was also found to have cytotoxic properties after being isolated from Patrinia heterophylla . Nigritanine is a compound isolated from S. nigritana that has been shown to exhibit antimicrobial activity against S. aureus .
S. axillaris contains α-Terpinene, which has been shown to have antihypertensive, antiulcer, antioxidant, anticancer effects [34, 35]. Limonene is also found in S. axillaris  and Kaempferol-7 glucoside isolated from S. nux-vomica  has been shown to have Anti-Inflammatory Activity [37- 39].
Brucine isolated from S. nux-vomica has been shown to have antitumor, anti-Inflammatory and analgesic effects [40-42]. S. nux-vomica contains 7-Hydroxy coumarin and has been shown to have antidiarrheal and antiulcerogenic properties [36-41].
Table 1. Report of antimicrobial efficacy of Strychnos species
Table 2. Report of phyto-compounds isolated from Strychnos species
In this study, thirty compounds were reviewed to be isolated from extracts of various plant sections of chosen Strychnos species. The antimicrobial properties of extracts from these Strychnos species were also reviewed, and they were found to be effective against the infections tested. It can be concluded that Strychnos species have wide variety of compounds based on information available from literature. These compounds essential belong to various classes of phytochemical, including alkaloids, terpenoid, terpene, steroids and other important classes. Hence, these compounds are reported to possess significant pharmacological properties.