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Although trace elements such as Iron is an essential nutrient of organisms, it is a toxic substance at high concentration for their growth and also change their metabolic patterns. In order to find out the influence of Iron on gram negative and gram-positive bacteria cells growth, the present investigation has been undertaken. In the series of experiments, B.cereus and E.coli incubated in NB-medium with and without Iron for 5 hours at 37?C. the result showed that addition 5.6 and 11.2 mg/li Fe+² or Fe+³ in medium (Inhibit) growth of B.cereus, but 11.2 mg/li Fe (II) or Fe (III) Inhibits of E.coli growth (P<0.001). These finding suggested that Iron is one of the necessary elements for microorganisms growth, but on the other hand Iron at high concentration has an toxic effect on their growth. B.cereus is more sensitive to toxic dose than E.coli.

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Background and Objective: Nanosilver particles are one of the functional nanotechnology filed. These nanoparticles have antibacterial characteritics. Combination therapy is one of new and specific therapeutic regiment in medicine. Eucalyptus plant is useful in growth inhibition of bacteria. This study was done to evaluate the inhibitory effect of alcoholic eucalyptus extract with nanosilver on E.coli growth. Materials and Methods: In this laboratory study, E.coli was cultured in nutrient agar medium. Primarily 50 l of bacteria was inocolulated in each plate, antibiograms disc contiminated with 3.1, 6.25, 12.5, 25 and 50 ppm concentration of nanosilver accompanied with 100% of etanolic extract of eucalyptus were placed in each plate subsequently. Diameter of inhibitory zone were evaluated following 24, 48, 72 hrs in 6th and 8th days. Data were analyzed using SPSS-15, ANOVA and Tukey tests. Results: After six days, inhibitory growth zone diameter of E.coli was 0.5 mm. This diameter in experimental group with 3.1, 6.25, 12.5, 25 and 50 ppm of nanosilver in combination with etanolic extract of eucalyptus were 0.55, 0.58, 0.82, 0.83 and 1.02 mm. Inhibitory growth zone in group of 12.5, 25 and 50 ppm of nanosilver was significant in compared to the control (P<0.05). Conclusion: The most proper time of inhibitory effect on E.coli growth is six day after treatment in combination of 50 ppm nanosilver particles with extract of eucalyptus.