Antimicrobial Activity of Aqueous and Ethanolic Extracts of Leaves of Walnut against Some Pathogenic Bacteria: A Laboratory Study

Walnut is a rich source of health-promoting flavonoids and phenolics with antimicrobial properties. The aim of this study was to evaluate the in-vitro antimicrobial effect of aqueous and ethanolic extracts of walnut leaf on Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria innocua.

Aqueous and ethanolic extract of walnut leaf were extracted by maceration method. The antimicrobial activity was evaluated through pour plate, disk diffusion agar, well diffusion agar, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). Data were analyzed by SPSS software and Duncan test (p < 0.05).

All the bacterial species were sensitive to the extract. In disk and well diffusion agar methods, S. aureus was the most sensitive bacteria to the aqueous and ethanolic extracts. The MIC of the aqueous extract of walnut leaf for Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria innocua was 50, 50, 25, 12.5 and 25 mg/ml, respectively. The MIC of the ethanolic extract of walnut leaf for Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Staphylococcus aureus and Listeria innocua was 50, 50, 25, 12.5 and 12.5 mg/ml, respectively. For all bacteria the MBC of aqueous and ethanolic extracts of walnut leaf was larger than the MIC.

The antimicrobial effect of the ethanolic extract was higher than the aqueous extract, and grampositive bacteria were more sensitive to the extract compared to the gram-negative ones. The aqueous/ethanolic extract of walnut leaf could be used as a natural antimicrobial.