Antimicrobial activity of crude extracts of three medicinal plants used in South-West Nigerian folk medicine on some food borne bacterial pathogens

Abstract

Three medicinal plants Trema guineensis Phyllanthus. discoideus, and Acalypha. wilkesiana traditionally used in South-West Nigerian communities for the treatment of gastroenteritis were investigated for antibacterial activity against strains of three food borne pathogens that resisted conventional orthodox antimicrobials. The extracts were screened against Salmonella enteritidis, Escherichia. coli and Stapylococcus aureus by standard methods. The results of antimicrobial activity showed that water and ethanol crude extracts were active on all the strains of pathogens tested at different concentrations, with ethanol extracts exerting more activity. Using the disc containing 20 mcg of the extracts, the average diameter zone of inhibitions observed against these organisms ranged from 10.6 to 13.1 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 32.5 & 35.3 and 31.5 & 33.0 mcg/ml were obtained for water and ethanol extracts of T. guineensis against S. enteritidis respectively, similar values were recorded against E. coli in this study. On the other hand, MIC & MBC values of 28.5 &39.2 and 28.5 &39.3 as well as 26.4 &35.6 and 27.0 &36.2 mcg/ml were recorded for water and ethanol extracts of A. wilkesiana and P. discoideus against S .aureus respectively, higher values were obtained against the strains of S. enteritidis and E. coli. Although, both water and ethanol extracts of the three medicinal plants were considered active on all the strains of the three food borne pathogens in this study thus justifying their traditional use as antimicribials, the extracts of T. guineensis seems to exert more activity on gram negative bacteria. All the plants extracts exhibited positive reactions to alkaloids, tannins, saponins, flavonoids and anthrapquinones but in variable degrees. None contained cardiac glycosides and cyanogenic glycosides.

Keywords: medicinal plants, antibacterial activity, foodborne pathogens, minimum inhibitory concentrations, Acalypha wilkesiana, Phyllanthus discoideus and Trema guineensis

African Journal of Traditional, Complementary and Alternative Medicines Vol. 3(4) 2006: 13- 22