Phytochemical and antimicrobial screening of crotalaria quartiniana a. Rich and erythrina melanacantha harms

ABSTRACT 

Information on the potency of many African medicinal plants against microorganisms is scanty, and in the current wave of antimicrobial resistance against chemotherapeutic drugs, there is need to search for plants that could be having phytochemicals that are resistance-free, affordable and with fewer and less side effects. The objective of this study was to investigate the phytochemical properties with respect to antimicrobial effects of the crude and pure components from extracts of Crotalaria quartiniana and Erythrina melanacantha against chosen available microorganisms. The different parts of the plants C. quartiniana and E. melanacantha were air dried and ground into fine powder. They were soaked sequentially using the solvents; n-hexane, dichloromethane, ethyl acetate and methanol. The soaked samples stayed for 48 hours, decanted and the extracts concentrated under reduced pressure in a rotary evaporator. The antimicrobial activity of the crude extracts obtained from C. quartiniana and E. melanacantha were tested against bacterial species of Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa clinical isolate. Cryptococcus neoformans, Trichophtyon mentagrophytes clinical isolates and Penicillium spp, Microsporum gypseum environmental isolates were fungal species used. Chloramphenicol was used as standard antibiotic with inhibition zone of 19 mm against P. aeruginosa and 24 mm against S. aureus. The hexane leaves, hexane stem bark and EtOAc root bark extracts of C. quartiniana showed moderate activity with MIC and (inhibition zones)of 0.125 mg/mL (12 mm), 0.5 mg/mL (10 mm) and 0.25 mg/mL (12 mm), respectively against S. aureus, with 0.0625 mg/mL (12 mm) and 0.5 mg/mL (11 mm) respectively against P. aeruginosa. The root bark hexane, DCM and EtOAc extracts of E. melanacantha showed moderate activity with MIC and inhibition zones of 0.125 mg/mL (15 mm), 0.25 mg/mL (15 mm) and 0.5 mg/mL (12 mm) respectively against P. aeruginosa. The hexane root bark extract showed 0.5 mg/mL (11 mm) against S. aureus. Fluconazole was used as standard antibiotic against T. mentagrophytes, C. albicans and M. gypseum with inhibition zones of 24, 18 and 22 mm, respectively. Moderate activity was shown by E. melanacantha MeOH stem bark extract with inhibition zones of 22, 11 and 16 mm, respectively against the fungi strains and MeOH stem bark extract had 18, 10 and 20 mm, respectively. There was high activity shown by EtOAc leaves extract of C. quartiniana with inhibition zones of 26, 18 and 20 mm, respectively. The isolation and purification of compounds was done using column chromatography and preparative thin layer chromatography to yield 3,9-dihydroxy-4,10-di-(γ,γ-dimethylallyl)pterocarpan (49) which showed inhibition zone of 10 mm against S. aureus, lupeol (100) and stigmasta5,22-dien-3-ol (100) which showed no activity, 3,9-dihydroxy-8-(γ,γdimethylallyl)pterocarpan (101) which showed inhibition zone of 15 mm against S. aureus and 20, 10 and 16 mm against T. mentagrophytes, C. albicans and M. gypseum respectively. Compound 3-(4-hydroxy-3-methoxy-phenyl)-acrylic acid undecyl ester (102) was also isolated and their structures elucidated using physical properties and spectroscopic methods. The reported antimicrobial results of the isolated compounds provide scientific evidence and validate their use in ethno medicine and may be potential sources for development of medicine by acting as natural template for development of new drugs that may be safe and effective to the community