Background and Aim:As ZnO is increasingly used in antibacterial applications, there is an urgent need for information on safety and potential hazards of manufactured NPs. One of the widely used tests in ecotoxicology to predicting the toxicity of chemicals is the Vibrio Escheri luminescence inhibition assay.In this study to find out how much safe is our laboratory made ZnO NPs, its inhibitory effect on bacterial growth and luminescent light output of Vibrio Escheri strain NRRLB-B1177 has been investigated. Methods:ZnO NPs synthesized by solvothermal method and dispersed in glycerol, as base fluid by the means of ammonium citrate.Minimum inhibitory concentration (MIC) was determined by micro dilution assay using ELISA reader apparatus. To investigate the side effects of ZnO NPs by bioluminescence inhibition assay and determine effective concentration of ZnO NPs that decrease intensity of luminescence light production in bacteria , several dilution of nanofluid inoculated in bacterial culture medium and then bacterial overnight culture added to them. Bacterial growth and intensity of bioluminescence light in presence of several concentrations of ZnO NPs measured by Berthold luminometer. Results:MIC for ZnO nanofluid against Vibrio Escheri was 100 Zg/ml and in this concentration growth inhibition percentage ( GI)% of ZnO NPs was 90%. Also effective concentration of ZnO NPs against bacteria that decrease luminescence light intensity more than 50%, during the first 10 hours of bacterial growth was 1 Zg/ml. This concentration did not have any obvious effect on bacterial growth. In several other studies were also used Vibrio fischeri, Vibrio harveyi and Pseudomonas fluorescens to determine luminescence inhibition percentage under influence of particular agents with potential of toxicity. Conclusion:ZnO NPs have antibacterial effect against V.fischeri. Toxic concentration became 100 fold lower than the amount of antibacterial concentration. Similar to this investigation can be used to test toxicity of several NPs or other chemicals.

Keywords