and Objective: Currently, many valuable drugs have lost their impact on Escherichia coli, and Escherichia coli drug resistance is the major reason for the treatment failure of nosocomial infections caused by this bacterium. This study aims to investigate the effect of silver nanoparticles using yogurt Lactobacillus flora on Escherichia coli with multiple drug resistance. Materials and Methods: This cross-sectional-experimental study was conducted in 2019 on Escherichia coli strain from some

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... ical centers in Ardabil, Iran. The isolates were performed based on approved biochemical tests to identify Escherichia coli bacteria. Antibiotic susceptibility testing was carried out by diffusion method. Then, its physical and chemical properties were determined by spectrophotometry (UV), SEM microscopy, and FESEM. Then, the synergistic effect of silver nitrate growth inhibitor was investigated using yogurt Lactobacillus flora by disk diffusion method according to standard (CLSI). Findings: In the present study, out of 100 samples, 37 strains of Escherichia coli were positive. The highest resistance of Escherichia coli isolates was to ciprofloxacin with 87% and the highest susceptibility was to nitrofurantoin with 76%. The size of silver nanoparticles according to the image of TEM and FESEM was both shown to be 16 nm in diameter. Silver nitrate using yogurt lactobacilli flora was able to reduce the combination of Escherichia coli strains with antibiotics, especially ciprofloxacin. Conclusion: The results of the present study showed that silver nanoparticles synthesized using yogurt lactobacilli flora with a diameter of 16 nm have antimicrobial activity against Escherichia coli. Considering the effectiveness of silver nanoparticles using yogurt Lactobacillus flora on ciprofloxacin-positive Escherichia coli, it can be used as a candidate drug against Escherichia coli in the future.