Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 11 3 2019 07 25 246 254 Navid Saidi Department of Microbiology, School of Medicine, Shahed University, Tehran, Iran Parviz Owlia Molecular Microbiology Research Center (MMRC), Shahed University, Tehran, Iran Seyed Mahmoud Amin Marashi Department of Microbiology, Qazvin University of Medical Sciences, Qazvin, Iran Horieh Saderi Molecular Microbiology Research Center (MMRC), Shahed University, Tehran, Iran 2019 01 15 2019 04 25 Background and Objectives: Staphylococcus aureus, as an opportunistic pathogen, is the cause of a variety of diseases from mild skin infections to severe invasive infections and food poisoning. Increasing antibiotic resistance in S. aureus isolates has become a major threat to public health. The use of compounds produced by probiotics can be a solution to this problem. Thus, the purpose of this study was to investigate the effect of Saccharomyces cerevisiae on some virulence factors (biofilm, α-hemolysin, and enterotoxin A) of S. aureus. Materials and Methods: Supernatant and lysate extracts were prepared from S. cerevisiae S3 culture. Sub-MIC concentrations of both extracts were separately applied to S. aureus ATCC 29213 (methicillin-sensitive S. aureus; MSSA) and S. aureus ATCC 33591 (methicillin-resistant S. aureus; MRSA) strains. Biofilm formation of these strains was measured by microtiter plate assay and expression level of α-hemolysin and enterotoxin A genes (hla and sea, respectively) using real-time PCR technique. Results: The supernatant extract has reduced both biofilm formation and expression of sea and hla genes, while lysate extract had only anti-biofilm effects. The MRSA strain showed more susceptibility to yeast extracts than MSSA strain in all tests. Conclusion: The present study exhibited favorable antagonistic effects of S. cerevisiae S3, as a probiotic yeast, on MSSA and MRSA strains. Based on the findings of this study, the compounds produced by this yeast can be used to control S. aureus infections; however, further similar studies should be conducted to confirm the findings of the present study. https://ijm.tums.ac.ir/index.php/ijm/article/view/2005 https://ijm.tums.ac.ir/index.php/ijm/article/download/2005/1169