Evaluation of antimicrobial activity and mode of action of Laportea aestuans extracts against urogenital, gut and pulmonary pathogens

Abstract

Phytochemical screening and antimicrobial activities of Laportea aestuans leaves, stem-bark and whole-plant aqueous, methanol and ethanol extracts were carried-out using standard phytochemical and microbiological methods. The phytochemical procedures indicated the presence of saponins, tannins, phlobatannins, flavonoids, alkaloids and cardiac-glycosides. The yields of the whole-plant extracts were significantly(p<0.05) higher than those of the leaves and stem-bark in the descending order of solvent polarity and solubility: aqueous>ethanol>methanol. The antimicrobial activities of the aqueous, methanol and ethanol extracts of Laportea aestuans leaves, stem-bark and whole-plant against the auchthocthonous urogenital, gut and pulmonary test organisms: Staphylococcus aureus, Staphylococcus saprophyticus, Streptococcus pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, Salmonella typhi, Vibrio cholerae, Shigella dysenteriae, Candida albicans and Aspergillus niger; assayed by the modified agar-well diffusion technique indicated broad-spectrum antimicrobial activities. Analysis of the antimicrobial activities of the extracts by activity-index, indicated that the leaf extracts, have significantly (p<0.05) higher antimicrobial activity than the stem-bark and wholeplant extracts in the descending sequence: leaf extracts > stem-bark extracts >whole- plant extracts. Similarly by activity-index, the ethanol extracts recorded significantly (p<0.05) highest antimicrobial activities compared to those of methanol and aqueous extracts, in the descending order ethanolextracts>methanol extracts>aqueous extracts. The minimum inhibitory concentrations (MIC) of the leaves extracts, assayed by the macrobroth-dilution technique was lowest against Shigella dysentariae (1.25 mg/ml),and generally between 2.50 - 5.0 mg/ml against the other bacterial and fungal species tested for both methanol and ethanol extracts; while the aqueous extracts was inactive. Equally, the minimum biocidal concentrations (MBC), and the establishment of mode of activity of the bioactive leaves extracts, assayed by the macrobroth-dilution technique, indicated predominantly static activity for the methanol extract, and a predominantly cidal activity for the ethanol extract. Both methanol and ethanol leaves extracts of Laportea aestuans showed significant (p<0.05) antimicrobial activities compared to the standard antibiotics: chloramphenicol and fluconazole.

Keywords: Antimicrobial potency, Activity –spectra, Laportea aestuans Extracts, Auchthocthonous urogenital, gut and pulmonary pathogens