Aim and Background: In recent years, science and industry have focused on preparing nanoparticles based on the principles of green chemistry. For this purpose, various types of biological structures such as bacteria, yeasts, and string molds are used. Due to the resistance of bacteria to antibiotics, the need to replace effective antimicrobials, with fewer side effects is less. The aim of this research was to synthesis the iron oxide nanoparticles by lactobacillus fermentum cytoplasmic extract and investigate its antimicrobial effects against Staphylococcus aureus and Pseudomonas aeruginosa.

Materials and Methods: In this study, after preparing cytoplasmic extract of Lactobacillus fermentum from frees-thow method, iron sulfate solution 10-3 M were added and incubated for 3 weeks in the presence of 5% carbon dioxide. Production of nanoparticles was investigated by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) and finally, the antimicrobial effects of standard strains of two bacteria (Staphylococcus aurous and Pseudomonas aeruginosa) were determined using agar diffusion method.

Results: Changing the color of solution to black is an indication of iron oxide nanoparticles production. The formation of iron oxide nano-crystals by Lactobacillus fermentum cytoplasmic extract was shown by XRD analysis and the average nanoparticles sizes that determined by transmission electron microscopy TEM were found to be about 10-15 nm with a spherical shape. The mean diameter of the no-growth field indicates that the synthesized nanoparticles inhibit Staphylococcus aureus in concentrations of 100 and 1000 mg/ml, while are ineffective against Psedumonas aeruginosa.

Conclusion: The use of cytoplasmic extract of Lactobacillus fermentum can be introduced as an effective biological method for the production of iron oxide nanoparticles and with more studies in this area, green nanoparticles may be used as suitable candidates for the treatment of microbial infections.