en Nutrition Nutrition پژوهشي Research <p style="margin: 0px; text-align: justify; line-height: 115%;"><strong>Background and Objectives: </strong><em>Melissa officinalis</em> belongs to plant Lamiaceae family and is native to Iran as well as other countries. The aim of this study was to identify chemical compositions and antioxidant activity of the <em>M. officinalis</em> essential oil (EO). Another aim of this paper was to assess antimicrobial activity of <em>M. officinalis </em>EO on growth of clinical and commercial strains causing infection.<br> <strong>Materials and Methods: </strong>Chemical compositions of the <em>M. officinalis </em>EO were analyzed using gas chromatography-mass spectrometry (GC-MS). The antioxidant potential was assessed using &beta;-carotene/linoleic acid inhibition and 2,2-diphenyl-1-picrylhydrazyl methods. The <em>total phenol content was</em> analyzed using <em>Folin</em><strong>-<em>Ciocalteu method. </em></strong>Antimicrobial activities of the <em>M. officinalis </em>EO were assessed using disk diffusion agar, well diffusion agar, micro-well dilution, agar dilution and minimum bactericidal concentration (MBC) methods.<br> <strong>Results: </strong>Major compositions of the <em>M. officinalis </em>EO included geranyl acetate (27.9 %), citral (14.2%), Z-citral (9.8%) citronellal (8.4%) and citronellol (7.6%). The total phenolic content and antioxidant potential of the <em>M. officinalis </em>EO included 51 &plusmn;0.50 mg GAE/g and 98 &plusmn;0.45 &micro;g/ml, respectively. Minimum inhibitory concentration (MIC) of the <em>M. officinalis </em>EO ranged 0.5&ndash;4 mg/ml, while the MBC ranged 1&ndash;8 mg/ml. A significant correlation was seen between the inhibition zone diameters (IZD) and concentration of the EO. The smallest IZD was reported for various concentrations of the <em>M. officinalis </em>EO on <em>Pseudomonas aeruginosa</em>.<br> <strong>Conclusions: </strong>In general, results showed that the <a name="_Hlk515296772"><em>M. officinalis </em>EO </a>included greater inhibitory effects on commercial bacterial strains causing infections, compared to those of clinical bacterial strains. The <em>M. officinalis </em>EO have the greatest effect on gram-positive bacteria. This compound is an effective free radical scavenger rich in phenolic compounds. Further studies are necessary to investigate toxicity of the <em>M. officinalis </em>EO due to its safety for human use.</p> Melissa officinalis, Microbial pathogenesis, Inhibition zone diameter, Chemical composition 17 25 http://nfsr.sbmu.ac.ir/browse.php?a_code=A-10-542-1&slc_lang=en&sid=1 Behrooz Alizadeh Behbahani behrooz66behbahani@gmail.com 10031947532846003438 10031947532846003438 No Department of Food Science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad Fakhri Shahidi fshahidi@um.ac.ir 10031947532846003439 10031947532846003439 Yes Department of Food Science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad