مقایسه اثرات ضد میکروبی غلظت‌‌های مختلف عصاره‌های الکلی رزماری (Rosmarinus officinalis)، علف چای (Hypericum Perforatum) و کاجیره (Carthamus Tinctorius) بر مراحل مختلف رشد باکتری اشرشیا کولی O157

  Background and Objectives : Medicinal plants have many therapeutic properties including antimicrobial effects with minimum side effects. The purpose of this study was to investigate the antibacterial effects of alcoholic extracts of three medicinal plants Rosmarinus officinalis, Hypericum perforatum, and Carthamus tinctorius on the growth curve of E.coli O157 . This strain is one of the most dangerous bacteria among gasterointestinal pathogenic micro-organisms.   Material and Methods : Leaves and dried flowering branches of rosmary, hypericum and carthamus were used for preparing various concentrations (0.2, 0.3 and 0.4 gr/ml) of alcoholic extracts. The antibacterial effects of these extracts against E.coli O157 were investigated utilizing well assay technique and spectrophotmetery. Statistical analysis was carried out by analysis of variance (ANOVA).   Results : At the first three hours of the experiment, alcoholic extraction of rosmary had an inhibitory effect at all three concentrations comparing to the other two extracts. The hypericum extract showed the least effect at this stage. However, after the first stage of treatment, the reverse results were observed so that E.coli O157 had the lowest growth rate at the presence of hypericum extract.   Conclusion : Based on the findings of this study, rosmary extract had a stronger antimicrobial effect and the other two extracs did not have substantial antibacterial effect on E.coli O157 although, inhibition zones were previously determined. Further investigations in this regard may shed more light on the field of clinical applications af medicinal plants for treatment of infectious diseases.   Key words: Rosmarinus officinalis, Hypericum perforatum , Carthamus tinctorius, E.coli O157, Growth curve     Funding: This research was founded by Ferdowsi University of Mashhad.   Conflict of Interest : None declared.   Ethical approval: The Ethics Committee of Ferdowsi University of Mashhad approved the study .   How to cite this article : Mashreghi M, Momtazi F . Comparison of the Antibacterial Effects of Various Concentrations of Alcoholic Extracts of Rosmarinus officinalis, Hypericum perforatum and Carthamus tinctorius on the Growth Phases of Esherichia coli O157 . J Rafsanjan Univ Med scie 2012 11(2): 103-14. [Farsi]