In-vitro antimicrobial potential of aqueous and methanolic extracts of Piper guineense and Gongronema latifolium on Staphylococcus aureus and Escherichia coli

Abstract

Plants are rich in different secondary metabolites, such as tannins, terpenoids and alkaloids which have been found in- vitro to have antimicrobial properties. The aim of this study was to determine the in-vitro antimicrobial potential of the methanolic and aqueous extracts of dried leaves of Gongronema latifolium and Piper guineense plants on Staphylococcus aureus and Escherichia coli. Soxhlet extractor was used for the methanolic solvent while cold maceration was used for the aqueous extraction. The phytochemical constituents of these extracts were screened thereafter the extracts were tested for their antimicrobial activity. The technique of agar well diffusion was employed. Wells was made on nutrient agar media and the extracts were placed in the well. Concentration of 1.25mg/ml, 2.5mg/ml, 5mg/ml and 10mg/ml were used. Surface of agar is inoculated (using sterile swab dipped into standardized broth culture of the test organism). Thereafter, the wells were bored into the inoculated agar and the extracts delivered into the well. After allowing for diffusion, the plates were incubated, after which the zones of inhibition around the well measured with the aid of vernier caliper. Activity of the extract against the test organism was expressed in terms of size (mm) of inhibition zone diameter around the well. The presence of alkaloids, flavonoids, tannins, saponins, and phenol in both plant extracts was observed. The aqueous extract of P. guineense and G latifolium showed more presence of phytochemical constituents than the methanolic extract and this is evidenced by higher zones of inhibition. Methanolic extracts of Piper guineense showed visible clearance suggestive of antibacterial activities by the extract only at 10mg/ml on S. aureus, but no form of inhibition on E. coli. Both extracts have concentration dependent antimicrobial effect on Staphylococcus aureus and Escherichia coli, and this may be due to phytochemicals found in them.