1. Introduction
In recent years, herbal medicine has gained numerous attention due to its relatively low side effect [1] . It was reported that about 80% of the world population especially in the developing countries, use herbs for the treatment of some disease [2] . Most pharmaceutical products depend on plants as the main source of material for their production [3] . Plant derived medicines can serve as a basis for the manufacture of different more active drugs [4] [5] . Most plants are made up of bioactive compounds such as lipids, phytochemicals, pharmaceutics, flavons, fragrances and pigments. According to World Health Organization, even developed countries are beginning to turn to plants for their medicine source due to the increased resistance of most existing antimicrobial drugs [6] .
Uses of Sclerocarya Birrea in Local Medicine
Sclerocarya birrea has been reported to have antiparasitic effect and can be used in the treatment of trypanosomiasis also known as African sleeping sickness [7] [8] . The methanolic extract of its leaves was reported to cause a complete mortality of the trypanosoma brucei in vitro [9] . In vitro antiplasmodial activity and in vivo antimalerial activity of Sclerocarya birrea was carried out against P. falciparum and P. berghe respectively. Results reported showed that P. falciparum was more sensitive to the extract compared to P. berghe, with the methanolic extract found to be more active than the water extract [10] . In south and east Africa, the stem-bark of Sclerocarya birrea is used as a potent remedy for dysentery and proctitis [11] . The Zulus of South Africa use a decoction of Sclerocarya birrea stem bark as a propylatic remedy against gangrenous rectitis [12] . Decoctions or steam from boiled are prepared roots and used for the treatment of heavy menstrual flow in women, bilharzias, cough, weakness, sore eyes, and in heart pains. [13] . Traditionally the stem bark is used for the treatment of various gastrointestinal disorder especially dysentery/diarrhea, hemorrhoid, stomach ulcers and pain, sore throat/mouth and toothache [14] . Both the methanolic and aquous extract of this plant was found to be anti-inflammatory in rats paw induced edema, and with some antioxidant activity [15] .
In this research we evaluate the antimicrobial activity and cytotoxicity of the stem bark of Sclerocarya birrea trona extract
2. Materials and Method
Fresh stem bark of Marula (Schelerocarya birrea) was aseptically collected from Doho Ward Kwami Local Government of Gombe State, Nigeria using a cleaned cutlass, and was transported in cleaned polythene bag and sacks to the lab in the Chemistry Department of Gombe State University. A soft brush was used to remove any dirt/debris from the plant materials. The fresh stem bark of marula was air-dried under a shade for two weeks for proper drying and stored in an air tide container for used. The plant was identified at the Gombe state university herbarium of the department of biological science with a voucher number 460.
2.1. Water-Trona Extraction (Decoction Method)
500 g of dried sample of marula stem bark and 2 g of trona were extracted by boiling in 2000 ml of distilled water for 60 minutes. The extracts were then filtered using Whatman Filter Paper No. 1, and the filtrate were concentrated using rotary evaporator, the crude extracts obtained were dried on a water bath and stored in an air tight container.
2.2. Phytochemical Screening
The phytochemical composition of the extracts of the plant materials were analyzed for the presence of saponins, steroids, tannins, flavonoids, alkaloids and glycosides according to standard methods [16] .
2.3. Antibacterial Activity
The antibacterial activity of the crude extract was determined in accordance with Agar-well diffusion method [17] . The test organisms (Echerichia coli, Klepsiella pneumoniae and Staphylococcus aureus) were collected from Microbiology Department, Gombe State University and were authenticated by biochemical tests. The test organisms were aseptically sub cultured on nutrient agar for twenty four hours inside of incubator at 37˚C. Using inoculation platinum wire loop, enough material from an overnight culture of the test organism was transferred into a test tube containing normal saline until the turbidity of the suspension matched the turbidity of the 0.5 McFarland Standard [18] . Sensitivity test was conducted following the agar-well diffusion method [17] .
2.4. Cytotoxicity Test
Brine Shrimp Lethality Test
Artemia salina nauplii (<48 hrs old) was exposed to a sample solution for 24 hrs and frequencies of immobility of the 10 nauplii in 5 ml solution were scored.
2.5. FTIR Analysis
The FTIR analysis of the two extracts was carried out in Gombe University, Faculty of Pharmaceutical Sciences. The FTIR spectra of the extracts which extracted with trona and the extract without trona were recorded in the range 4000 - 450 cm−1 using Perkin Elman Spectrum version 10.03.06.
3. Results and Discussion
3.1. Phytochemicals Screening
The result shown on Table 1 indicated that marula stem bark extract contains tannins, alkaloids, and saponins while flavonoids, steroids, and glycosides are absent. The results of the current research are in agreement with the one reported by Kutama et al., (2013) [19] , with an observed difference which might be due to the difference in method of extraction, trona, high temperature and sample sizes.
3.2. Antimicrobial Activity
The result of antibacterial study of the stem bark of Sclerocarya birrea (marula) and the standard antibiotic used are presented in the Table 2. The aqueous extract with trona was found to be effective in inhibiting the growth of the three tested bacteria as demonstrated by an agar well diffusion method. The aqueous extract shows higher zone of inhibition at a concentration of 100 mg/ml, and the zone of inhibition increases with the increase in concentration of the extract.
3.3. Cytotoxicity Test
The result obtained from cytotoxicity of the marula stem bark extracts using brine shrimp lethality assay as shown in Table 3 shows that the effects of the
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Table 1. Results of phytochemicals screening of marula stem bark with trona.
Key: + = Present; − = Absent.
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Table 2. Results of antimicrobials activity of marula stem bark extract with trona.
Key: NA = No activity.
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Table 3. Result of Brine Shrimp lethality assay of extracts with trona.
crude extract of Sclerocarya birrea on the mortality rate of the brine shrimp (Artemia salina) depend on the types of crude extracts and its concentration. For aqueous extract with trona 9 nauplii died upon exposure at 1000 ppm whereas at 100 ppm and 10 ppm 6 and 3 nauplii died. This indicates that the number of mortalities increases with the increase in concentration of the extract and aqueous extract with trona has lethal concentration for 50% mortality (LC50) value of 63.1 ppm. Values of the LC50 greater than 1000 ppm indicates poor activity, and values lower than 1000 ppm indicates higher activity of the plant extract [20] .
4. Conclusion
An improved actibacterial activity was obtained from the trona extract of the neem stem bark. The extract was found to have potential for the treatment of diseases related to Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae with high efficiency. Since the activity of a plant extract is mostly related to the values of LC50 such that values below 1000 ppm are found to be active and values above 1000 ppm are found to be inactive, with the obtained value of 63.1 ppm, we can say that the plant extract is active and effective as an anti-bacteria for the treatment of diseases caused by Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae.
Acknowledgements
We wish to acknowledge the contributions of the botany department of Gombe state University, the microbiology department of Gombe State University, and the chemistry department of Gombe State University for providing us with the laboratory space for this experiment.