fa تحقيقي Original Paper <div><strong>ABSTRACT</strong><br> <strong>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Background and Objectives:</strong> Silver nanoparticles (AgNPs) have physical and surface properties that could threaten human and environmental health. AgNPs are classified as &lsquo;very toxic&rsquo; to eukaryotic organisms&nbsp;and are less toxic to bacteria. The aim of the present study was to study the effects of different sub-minimum inhibitory concentrations (MICs) of AgNPs on some virulence factors of <em>Staphylococcus aureus</em> as a pathogenic bacterial model.<br> <strong>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Methods: </strong>Tube double serial dilution method was used to determine MIC of AgNPs against standard strain and ten field isolates of <em>S. aureus</em>. Tube cultures of isolates in LB broth were supplemented with different concentrations of AgNPs and were incubated at 37 &deg;C with constant shaking under aerobic conditions. Samples from each tube were streaked on blood agar plates and assay for hemolysins, coagulase and DNase production were performed.<br> <strong>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Results:</strong> The MIC of AgNPs against all examined isolates was determined as 50 &micro;g/mL. The results showed that 1/2, 1/4 and 1/8 MIC of AgNPs had no negative effect on DNase and coagulase production but inhibited alpha- and beta-hemolysin production in most isolates (64-91%). In addition, production of delta-hemolysin was inhibited by 1/2 MIC of AgNPs.<br> <strong>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Conclusion:</strong> The effects of sub-MIC of AgNPs on bacterial growth appear at 4-8 hours post-exposure and then the bacteria follow a normal growth trend. This toxic effect may affect ecosystems species.<br> <strong>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Keywords:</strong> Silver particles, Minimum inhibitory concentration, Virulence factors, <em>Staphylococcus aureus</em>.</div> Silver particles, Minimum inhibitory concentration, Virulence factors, Staphylococcus aureus. 7 11 http://mlj.goums.ac.ir/browse.php?a_code=A-10-1-526&slc_lang=fa&sid=1 Azizollah Ebrahimi A_kahrizsangi@yahoo.com 100319475328460014489 100319475328460014489 Yes Department of Pathobiology, School of Veterinary Science, Shahrekord University, Shahrekord, Iran Younes Daryalal 100319475328460014490 100319475328460014490 No Department of Pathobiology, Veterinary College, Shahrekord University, Shahrekord, Iran Mohamadreza Mahzounieh 100319475328460014491 100319475328460014491 No Department of Pathobiology, School of Veterinary Science, Shahrekord University, Shahrekord, Iran Sharareh Lotfalian 100319475328460014492 100319475328460014492 No Department of Pathobiology, School of Veterinary Science, Shahrekord University, Shahrekord, , Iran