Background: The production of novel antibiotics inhibiting virulence factors of pathogenic bacteria has emerged as a promising approach to combat the emergence of resistant strains. Acknowledging the harmful effect and considerable spread of pathogenic strains of Escherichia coli, this research aimed at investigating the inhibitory effects of biologically synthesized silver nanoparticles on the growth of E. coli and its negative impact on capsule formation as the virulence factor of the pathogen. Methods: Silver nanoparticles were synthesized by the addition of silver nitrate to a fresh culture of Shewanella oneidensis. The inhibitory effect of the nanoparticles on E. coli growth was investigated by serial microdilution method. The expression of alphahemolysin (hly) under nanoparticle treatment was quantitatively evaluated using a real-time PCR. The growth rate of E. coli under nanoparticles treatment was monitored at a 12-hour interval. Results: It was revealed that monodisperse spherical silver nanoparticles were produced to significantly inhibit the bacterial growth at a concentration of 50g/mL (MIC = 50g/mL). Furthermore, the expression of alpha-hemolysin (hly) was downregulated by the nanoparticles even at concentrations below the MIC value. Conclusions: In general, the research findings revealed that silver nanoparticles produced by green approach could be used as appropriate candidates for the development of new antibacterial medicines.

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