Abstract

This work aims to evaluate the antimicrobial potential of ethanolic extracts of Neem leaves and guava leaves.The antibacterial activity of guava (Psidium Guajava) and Neem (Azadirachta Indica) extracts against Staphylococcus Aureus, Escherichia coli,, Salmonella typhimurium, Vibrio cholerae and Bacillus cereus Guava and Neem extracts showed higher antimicrobial activity against Gram-positive bacteria compared to Gram-negative bacteria except for V. Parahaemolyticus, P. Aeruginosa, and A. Hydrophila. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Grampositive bacteria (Bacillus cereus, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Salmonella typhimurium, and Vibrio cholera. The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH and membrane potential were measured in Staphylococcus aureus (SA) and Escherichia coli (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pH as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can be used safely as food preservatives.