The use of medicinal plants to manage various ailments affecting humans have been  in  existence  since ancient times. Studies have shown that in Africa, about 80% of the population rely  on medicinal plants for the management of various ailments (Agyare et al., 2009). It is therefore important that such plants should be investigated to better understand their properties, safety and efficacy.

Morinda is a genus of flowering plants of the family, Rubiaceae (Umberto, 2000). In Ghana, the plant is used in managing ailments such as diabetes, hypertension, cerebral congestion, dysentery, stomach-ache, leprosy and gonorrhoea. Traditionally, the stems are used to treat piles while the leaves are used to treat fever (CSIR-FORIG, Ghana, 2017). Extracts of the plant have shown anti-inflammatory, febrifuge and pain reducing activity as well as antimalarial activity (Dalziel, 1973; Awe and Makinde, 1998). Methanol and ethanol extracts of the leaves of Morinda lucida have also been shown to possess antidiabetic activity (Bailey and Day, 1989). The leaves of the plant have also demonstrated trypanocidal activity (Asuzu and Chineme, 1990).

Garcinia cola (Guttiferae) is a multipurpose tree crop with increased value for the medicinal use of its parts. It is known as a wonder plant since every part of it has a medicinal importance. The seeds are chewed as an aphrodisiac or used to cure cough, dysentery, or chest colds in herbal medicine (Irvine, 1961). The latex or the gum is used internally against gonorrhoea and applied externally on fresh wounds (Iwu, 1989). The sap is used in curing parasitic diseases. The stem is used to produce bitter chewing sticks which is chewed chiefly as a masticatory to set an action of nervous alertness and has also been proven to exhibit pharmacological uses in treating coughs and throat infections (Farombi et al., 2005). G. cola serves as a source of raw material in the pharmaceutical industry; the raw stem bark can be used as a purgative, the powdered bark applied on malignant tumours (Iwu, 1989). G. cola exhibits purgative, antiparasitic, anti-inflammatory, antibacterial and antiviral properties (Ogunmoyole et al., 2012). Biflavonoid isolates, kolaviron, extracted from G. cola seeds were tested on streptozotocin (STZ)-diabetic rats. This study confirmed that cardiac, renal and hepatic function indices were significantly elevated during STZ-induced diabetes and that oral administration of kolaviron reduced the levels of some of the indices. Therefore, kolaviron may offer protection for tissues of animals during diabetes (Adaramoye, 2012). G. cola seeds have been reported to have an anti-inflammatory activity (Olaleye et al., 2000).

Although a lot of work has been done on the other parts of these plants, very little research has been conducted on the stem bark of these plants. This study therefore aims at evaluating the anti-infective and antioxidant properties of these plants and to justify or otherwise their folkloric uses. 

The turbidity of the actively growing broth cultures was adjusted with sterile distilled water to obtain a turbidity optically comparable to that of 0.5 McFarland Standard.

Micro-dilution assay

The minimum inhibitory concentration (MIC) was determined by the micro broth dilution method using 96 well microtitre plates (Eloff, 1998). A quantity of 50 µL of the double strength nutrient broth was used to fill each well. A volume of 5 µL of 24 h organism suspension was added as well as calculated volumes of the extracts, standard drugs (Ketoconazole and Ciprofloxacin)  and sterile water to give a final well volume of 100 µL with varying extract and standard concentrations per well. The concentrations of extracts prepared ranged from 100 to 20 µg/mL.  The microtitre plates were covered and incubated at 37°C for 24 h.  A volume of 20 µL MTT (3-(4.5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) solution was added to the wells. The MIC was determined as the lowest concentration that inhibited the growth of the organisms which was indicated by the absence of purple coloration upon addition of the MTT solution.

Evaluation of anthelmintic activity

Collection of worms

Adult Indian earthworms were collected from the soil in a water logged area in Tema Community 10 and cabbage farms at Miotso near Central University, Ghana. The earthworms of length approximately 7 to 12 cm and width, 0.2 to 0.6 cm were used for the experiment due to their anatomical and physiological resemblance to human intestinal roundworm parasites and also because of easy availability; they are used extensively for the preliminary in vitro evaluation of anthelmintic compounds (Tiwari et al., 2011). The earthworms were washed with distilled water to rid them of debris.

Anthelmintic bio-assay

The worms were divided into eight groups each comprising of four earthworms. Ten millilitres of each extract solution of concentrations 10, 20 and 50 and mg/mL were prepared for both GBC and MLB using distilled water. Concentrations of 20 mg/mL albendazole and 15 mg/mL piperazine citrate were used as reference standards. All the samples and the standard drugs were freshly prepared before commencement of the experiments. The washed earthworms were placed in Petri dishes containing 10 mL of the respective formulations and concentrations. Observations were made for the time taken for paralysis and death of individual worms. Paralysis was noted when the worms ceased to move but were revived when shaken or placed in warm water at 50°C. Death was noted when the worms lost motility coupled with a fading away of their body colour. Normal saline was used as a negative control and the respective death and paralysis times were recorded (Bhawar et al., 2009).

Statistical analysis

All results and graphs were plotted and analysed using the Graph Pad Prism 5.0 for windows (Graph Pad software, San Diego, CA, USA).

Phytochemical screening

The phytochemical screening revealed the presence of glycosides, saponins, alkaloids, tannins and flavonoids in the extracts of MLB and GCB.

Antimicrobial activity

GCB and MLB extracts both demonstrated broad spectrum antibacterial and antifungal activity against the selected microorganisms. The antimicrobial activity was more profound in MLB as indicated in Table 1.

Antioxidant activity (free radical scavenging activity)

The antioxidant activity of GCB was highly profound as indicated in the IC₅₀ value obtained (Table 2, Figure 1). MLB however showed poor antioxidant activity. The lower the IC₅₀ value the more potent the antioxidant activity. 

Anthelmintic activity

Both extracts demonstrated a concentration dependent anthelmintic activity as shown in Table 3.

Phytochemical analysis of the extracts of both plants revealed the presence of tannins, saponin glycosides, anthraquinones, cardiac glycosides, alkaloids and flavonoids. Natural antioxidants are mainly obtained from plants rich in phenolic compounds such as flavonoids, phenolic acids and tocopherol (Ali et al., 2008). Phenolic compounds possess biological properties such as anti-apoptosis, anti-aging, anti-carcinogen,  anti-inflammation, anti-atherosclerosis, cardiovascular protection and improvement of endothelial function as well as inhibition of angiogenesis and cell proliferation activities (Han et al., 2007). Flavonoids have also been found to have anti-microbial activity against a wide array of microorganisms (Pistelli and Giogi, 2012; Cushnie and Lamb, 2005).

The stem bark extract of M. lucida serves as a reservoir of bioactive phytochemical compounds. The results as shown previously confirm other studies conducted on this plant part (Fasola and Ogunyomi, 2005; Adomi and Umukoro, 2010). The M. lucida extract showed broad spectrum antibacterial activity as well as antifungal activity against selected microbes. The antimicrobial activity could be attributed to flavonoids and tannins present in the extracts (Gomes de Melo et al., 2010). The antioxidant activity exhibited could be attributed to the phenolic compounds in the plant (Kahkonen et al., 1999).

Various research works have been done on different parts of G. cola including the seeds, fruits, roots and leaves. However, very little research has been conducted on the stem bark of the plant.  The stem bark extract demonstrated broad spectrum antibacterial activity as well as antifungal activity which could be attributed to the secondary metabolites as stated previously. Studies conducted by Ogunmoyole et al. (2012) on the seeds and fruit extract respectively have shown antioxidant activity. The stem bark extracts as used in this experiment also demonstrated antioxidant activity with IC₅₀ value (6.830 µg/mL) almost comparable to that of ascorbic acid (2.929 µg/mL).

This gives an indication of the possible high level of phenolic compounds present in the stem bark hence the high antioxidant activity. G. cola bark extracts also demonstrated a concentration dependent anthelmintic activity with higher concentrations demonstrating better anthelmintic activity. Studies have largely attributed the anthelmintic activities of plants to the presence of tannins. Tannins are believed to interfere with the energy generation of the helminth parasite by uncoupling oxidative phosphorylation or by binding to free proteins in the gastrointestinal tract of the helminth. This eventually results in death of the parasite (Adu et al., 2015; Olusegun-Joseph et al., 2012).

Stem bark ethanol extracts of M. lucida and G. cola possess broad spectrum antibacterial and antifungal activity. Both extracts also possess antioxidant and concentration dependent anthelminthic activities. This could justify their use in folkloric medicine for the management of various ailments. 

The authors have not declared any conflict of interests.

Authors acknowledge the contributions of Mr. Kwame Koomson, Mr. Christopher Kyei-Mensah and Mr. Harry Oblie Laryea who are laboratory technicians at the Central University School of Pharmacy for their technical support.