Effects of some essential oils against growth and biofilm production of two plant pathogenic bacteria, Pectobaterium carotovorum and Pectobacterium atrosepticum

Plant–derived essential oils (EOs) are a major group of environments–friendly compounds with antibacterial properties that have been used during the last decade. This study aimed to identify the chemical composition and evaluate the antimicrobial activity of EOs from Lippia citriodora, Origanum vulgare, Phlomis fruticose, Satureja spicigera, and Syzygium aromaticum against two soft rot– including bacteria, Pectobacterium carotovorum and Pectobacterium atrosepticum. Plants were collected from Khuzestan province, and their essential oil composition was determined from gas–chromatography–mass spectrometry (GC–MS) analysis. The antibacterial effect of Eos was measured by the disk diffusion method. The effect of EOs on biofilm formation was also assayed. In addition, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were calculated accordingly. The interaction among the EOs was calculated according to the fractional inhibitory concentration (FIC) index using the Modified Dilution Checkboard method. The result showed that all Eos inhibited bacterial growth. The highest MIC (31/25) was attributed to P. fruticosa against P. carotovorum while the lowest MIC (125) belongs to L. citriodora and S. spicigera against P. carotovorum. FIC index showed that L. citriodora and S. spicigera are neutral to P. carotovorum. Analysis of GC–MS chromatogram indicated that the major constituents of P. fruticosa, L. citriodora, O. vulgare, S. spicigera, and S. aromaticum were cis–Thujone (17.47%), Isogeraniol (23%), cis Piperitone oxide (29.5%), Carvacrol (88.5%), Eugenol (98.7%), respectively. According to the results, in high MIC of Eos (125 ppm), bacteria were not able to form biofilm. Our results indicate that these five plant species have antimicrobial activity against Pectinbacterium species. Among all Eos used, L. citriodora and P. fruticose showed the highest activity which, therefore, can be recommended for further applications.