COMPARATIVE STUDIES ON THE PHYTOCHEMICAL AND ANTIMICROBIAL PROPERTIES OF Rauwolfia vomitoria AND Crotalaria retusa LEAF EXTRACTS

Abstract

The antimicrobial activities of methanol and acetone leaf extracts of Rauwolfia vomitoria (Swizzle stick) and Crotalaria retusa (Rattle weed)were investigated against fifteen(15) pathogenic bacteria and three (3) fungi using the cold extraction method.The extracts were investigatedfor their phytochemical components both quantitatively and qualitatively. The minimum inhibitory concentration (MIC) was determined using standard the method.The crude extracts were partially purified by column chromatography and fractions obtained were spotted unto thin layer chromatography. Fractions that have the same refractive factors (Rf) were bulked together and tested against the test organisms for antimicrobial activities. The bioactive fractions were subjected to Infra- red analysis (IR) to obtain the functional groups present in them. Results show that, all test microorganisms were susceptible to the methanol extract of Rauwolfia vomitoria with Staphylococcus aureus (NCIB 950) having the highest zone of inhibition of 16.33±0.33mm and K.peumoniae ATCC (25922) the least zone of inhibition of 6.67±0.33mm. However, Staphylococcus aureus andBacilllus cereus showed resistance to methanol extract of Crotalaria retusa. All the fungal isolates were susceptible to the extracts with the zone of inhibition ranging from 4mm to 11mm. The results of the phytochemical screening for both extracts showed the presence of tannin, flavonoid, steroid, terpenoid, saponin, and cardiac glycosides except for saponin that was absent in acetone extract of Crotalaria retusa. Terpenoid was the most abundant in methanolic extract of Rauwolfia vomitoria (22.39±22.47mg/g).The (MIC) ranged between 3.13 and 25.00mg/ml. The (MIC) for the methanolic extract of Rauwolfia vomitoria on Bacillus cereus, S.aureus and Methicillin resistant Staphylococcus aureus (MRSA) showed the lowest concentration of 3.13mg/ml while the lowest MIC of 3.13mg/ml was recorded for Salmonella typhi (ATCC 33458) by the methanolic extract of Crotalaria retusa. The test isolates were more susceptible to the partially purified extracts in comparism to the crude extracts. Staphylococcus aureus (NCIB 950) had the highest zone of inhibition of (32.00±0.33mm) for the partially purified extract of Rauwolfia vomitoria while it recorded (16.33±0.33mm) for the crude extract. Functional groups of the bioactive components showed bands corresponding to different peaks revealing hydroxyl, aromatic and carbonyl groups. Generally, the extracts had better antimicrobial activities when compared with the the antibiotics used.The leaves of Rauwolfiavomitoriaand Crotalaria retusa have broad spectrum activities which have great potential as antimicrobial compounds against microorganisms that may be of great use for the development of pharmaceutical industries.It can be use as a therapy against various diseases especially infectious diseases caused by methicilllin resistant Staphylococcus aureus (MRSA). The demonstration of their antimicrobial activity against the test isolates is an indication that there is possibility of sourcing alternative antibiotic substances in these plants for the development of newer antibacterial agents.