The study of the antimicrobial activity of colloidal silver nanoparticles against Bacillus spp and Vibrio harveyi and their gtrowth kinetic assay

Microbial infections outbreak in aquatics are important challenges, and farmers have major difficulties dealing with microbes especially regarding their antibiotic resistance. The purpose of this study was comparative evaluating of antimicrobial activity of silver nanoparticles (Ag NPs) against one gram-positive bacteria (Bacillus spp) and a gram-negative (Vibrio harveyi). In this experimental study, the antibacterial effects of Ag NPs was determined by agar well diffusion method through the measurement of the inhibitory zone diameter and micro-broth dilution for determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). According to the results of well diffusion test in agar, the maximum diameter of inhibition zone (44.6 ± 0.15 mm) was related to Bacillus spp. MIC of Ag NPs against Bacillus spp and Vibrio harveyi  were 1.95 and 3.91 mg/ml respectively and MBC was recorded 3.91 mg/ml for both bacteria. Also the kinetic study confirmed the results, So that growth of Bacillus spp 5 hours and V. harveyi 6 hours after exposure to silver nanoparticles was stopped.This study showed that colloidal Ag NPs have higher bactericidal effects on gram-positive bacteria compared with gram-negative bacteria and of course can be a candidate for the elimination of both gram negative and gram positive bacteria, especially in control of infective aquatic microorganisms.