Herbs have been used for its medicinal properties from several thousand years ago. Herbs, essences and extracts, possess a variety level of biological activities and antimicrobial activities of a large number of them have been proved. Eucalyptus is one of these plants which the anti-virus effects of its extract has long been used to treat influenza and colds in most parts of the world. The aim of this study is evaluating antimicrobial effects of aqueous and alcoholic Eucalyptus camaldulensis leaves against some of the important food pathogens. Antimicrobial effects of extracts were evaluated on Staphylococcus aureus PTCC 2592, Escherichia coli PTCC1330 and Penicillium digitatum by ―using the method of Collins‖ and ―disk agar diffusion method‖. The results showed that aqueous and ethanolic extract were quite effective in 2000 μg/ml concentration on Staphylococcus aureus and Penicillium digitatum, while both extracts have no certain antimicrobial effect on Escherichia coli. In ―disk agar diffusion method‖ 20, 40, 60 and 80 mg/ml aqueous and ethanolic extract concentrations, was inhibition effect on Staphylococcus aureus and Penicillium digitatum, and 60 and 80 mg/ml aqueous and ethanolic extract concentrations, has deterrent effect on Escherichia coli, but at 20 and 40 mg/ml concentrations, no inhibitory effect on Escherichia coli was observed. Minimum Inhibitory Cconcentration (MIC) of ethanolic extract of Eucalyptus camaldulensis leaves and Minimal Bactericidal Concentration (MBC) for bacteria and Minimum Fungicidal Concentration (MFC) for fungi were performed. The results indicate that ethanolic and aqueous extracts of Eucalyptus camaldulensis leaves have the greatest effect on gram-positive bacteria Staphylococcus aureus. Escherichia coli were resistant to most of the aqueous and ethanolic Eucalyptus camaldulensis extracts. In conclusion, using Eucalyptus as a natural antimicrobial compounds in vitro have considerable antimicrobial ability over the studied strains.

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