Abstract

---

Medicinal plants represent potential sources of new antibacterial agents against drug resistant bacteria. The aim of this study was to investigate the antibacterial activities of aqueous and ethanol extracts of the leaves of Moringa oleifera and Alchornea cordifolia against strains of Pseudomonas aeruginosa expressing various virulence and biofilm-forming characteristics. Five hundred grams (500 g) of each of the powdered plant materials was soaked in 1,500 ml of ethanol/water respectively for 24 h at room temperature. The extracts were filtered using non-adsorbent muslin cloth into a clean beaker. The filtrates were dried by evaporating off the solvent at 50 oC in a hot air oven. The inhibitory activities of the extracts were tested against the strains using the agar well diffusion and microbroth dilution assays. The crude ethanolic and aqueous extracts of the leaves of Moringa olifera and Alchornea cordifolia produced inhibition zones ranging from 10.0 mm to 20.0 mm at a concentration of 200 mg/ml. The extracts of Alchornea cordifolia had higher inhibitory effects on all the test isolates. The antibacterial activities of the extracts varied according to the genetic determinants carried by the various strains with the zone sizes decreasing to between 7.5 mm to 13.0 mm for some strains. The wild-type strain (PA14-GFP) carrying the green fluorescent protein was susceptible to the aqueous and ethanol extracts of both plants while some of the strains carrying mutations for biofilm formation were less susceptible to the plant extracts. It is remarkable that the ethanol extract of A. cordifolia had appreciable inhibitory activity against all isolates including strains like PA01-L-wt-PqSR and PA01-L-wt which carry mutations for biofilm formation. The minimum inhibitory concentration against these strains ranged from 6.25 mg/ml to 25 mg/ml while the minimum bactericidal concentration was between 12.5 mg/ml for the ethanol extracts and 25 mg/ml for the aqueous extracts. Findings of the study provides justification for further research on the potentials of these medicinal plants as sources for antibacterial and antibiofilm compounds.

Keywords: Antibacterial, Biofilm, Alchornea, Moringa, Antibiotics