Continuous and indiscriminate use of chemical drugs causes an important phenomenon of resistance to microorganisms and consequently, the effect of the drugs is weakened or neutralized. On the other hand, it has been reported that many plant essential oils have a significant inhibitory effect on pathogenic microorganisms, so, this study aimed to evaluate the antioxidant and antimicrobial activity of several plant extracts on Escherichia coli isolated from poultry feces. Cichorium intybus L., Hypericum perforatum L., Lavandula angustifolia Mill., and Thymus vulgaris L. from Shahrekord were collected and determined in the botanical laboratory of University of Zabol. To prepare the ethanolic extract, 40 gr of dried leaves of plants used in 400 cc of ethanol were used. The various strains of E. coli used were isolated from poultry feces by biochemical, bacteriological, and growth tests as well as standard tests. Determination of the free radical trapping activity was perfomed bydiphenylpicryl hydroxyl, and then the antimicrobial effects were investigated by diffusion method in Muller Hinton agar medium using 6 mm paper discs according to Bauer and Kirby instructions. Statistx ver10 software was used for statistical calculations. Mean comparisons were performed using the least significant difference (LSD) test. The results showed an increasing trend of the antioxidant activity of the extracts with increasing the concentration of plant extracts. The interaction of plant extract and the amount of extract in trapping free radicals showed that the highest antioxidant activity at low concentrations of the extract (16 and 32 mu g/ml) was observed in the chicory extract following by licorice extract, but it licorice extract showed the highest activity at high concentration (64 mu g/ml). In general, H. perforatum L. was the most effective plant in trapping free radicals. The lowest MIC of H. perforatum L. was 3.1 ppm, which was unilaterally inhibited at this concentration. H. perforatum L. and chicory had the highest (5.38) and lowest (2.23) diameter halos of inhibition of E. coli growth. Considering the side effects of chemical drugs and antibiotics as well as the potential effect of medicinal plant extracts used, especially H. perforatum L. on E. coli, compared to Cefazolin, it is recommended to use H. perforatum L. in inhibiting growth of E. coli.
