PHYTOCHEMICAL ANALYSIS AND EVALUATION FOR ANTIMICROBIAL ACTIVITIES OF THE EXTRACTS OF Psidium guajava L. AND Calpurnia aurea (Ait.) Benth, AGAINST SELECTED HUMAN BACTERIAL PATHOGENS

Abstract

Plants are rich in a wide diversity of secondary metabolites which have been found to exhibit antimicrobial, antioxidant and antitumor activities. Guava (Psidium guajava L., Myrtaceae) and (Calpurnia aurea L. Fabaceae) are known for their traditional medicinal values. These studies were conducted with the objective of analyzing the secondary compounds profile of the two plant species and evaluate their antimicrobial properties on selected human bacterial pathogenes. Extraction was done by maceration using ethanol solvent. Qualitative analysis of phytochemicals was carried out using standard protocols and phytochemicals were quantified from leaf and bark extracts or powders using Spectrophotometric or gravimetric method. Antibacterial activities of leaf and bark extracts were determined by disc diffusion and broth dilution methods. Results of qualitative analysis showed that both plants have tannins, steroids, saponins, terpenoids and alkaloids in their leaves and barks. Whereas flavonoids and phlobatannins were absent in both plants' leaves and barks extracts. There was significant concentration difference between the different types of compounds analyzed from leaves and barks of both plants. Saponins were found to be higher in both P. guajava and C. aurea leaves followed by total terpenoids, alkaloids, total phenols and tannin. In barks of both plants, however, total terpenoids was highest followed by saponins, alkaloids, total phenols and tannins. Each group of compound also varied significantly (P<0.05) on different parts of both species. Both plants' bark extracts had significantly higher crude phenolic contents than that of leaf extracts, and both plants' leaf extracts had significantly higher crude tannin contents than that of bark extracts. Whereas both plants' bark extracts had significantly higher saponin content than both plants' leaf extracts. Leaf extract had generally higher contents of quantified phytochemical than bark extracts. Comparison between extracts and control (ethanol with no inhibitory effect (0mm ZOI) showed that all extract types significantly inhibited the growth of all bacterial isolates. However, the isolates showed sensitivity difference to extracts. When compared with commercial antibiotic however, all extracts performed less in inhibiting bacterial growth. Generally the MIC required to inhibit growth ranged from 25-100mg/ml and the MIC required to suppress growth of the isolates varied with bacterial species and extract type. The leaf and bark extracts of each plant also showed different MIC to suppress growth of the tested bacteria. In both plants, leaf extracts showed more antibacterial activities against all tested isolates than bark extracts. Overall, this study showed that both Psidium guajava and Calpurnia aurea have potential compounds that can help manage the growth of these clinical isolate bacterial pathogens and isolation and identification of specific potent compound(s) is required in the future.