Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 3 1-2 2015 10 13 1 7 EN Mohsen Mirzaee Department of Bacteriology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, IR Iran. Shahin Najar-Peerayeh Department of Bacteriology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, IR Iran. Mehrdad Behmanesh Department of Genetics, School of Biological Science, Tarbiat Modares University, Tehran, IR Iran. Mahdi Forouzandeh-Moghadam Department of Genetics, School of Biological Science, Tarbiat Modares University, Tehran, IR Iran Abdol-Majid Ghasemian Department of Bacteriology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, IR Iran. 2015 10 12 2015 10 12 Background: In fact the biofilms are composed of bacterial cells living inmulticellular structures such as tissues and organs embedded within a self-produced matrix of extracellular polymeric substance (EPS). Ability to attach and biofilm formation are the most important virulence factors Staphylococcus aureus isolates. The aims of this study were to detect intracellular adhesion (ica) locus and its relation to the biofilm formation phenotype in clinical isolates of S. aureus isolated from bloodcultures. Methods: A total of 31 clinical S. aureus isolates were collected from Loghman Hospital of Tehran, Iran. In vitro biofilm formation ability was determined by microliter tissue culture plates. All clinical isolates were examined for determination the ica locus by using PCR method. Results: Twelve (38.7%) of the isolates were strong biofilm producers. The results showed that 18(80.6%) of the isolates carried icaD gene, whereas the prevalence of icaA, icaB and icaC were 51.6%, 45.1% and 77.4% respectively. Conclusions: S. aureus clinical isolates have different ability to form biofilm. This may be caused by the differences in the expression of biofilm related genes, genetic make-up and physiological conditions. https://jmb.tums.ac.ir/index.php/jmb/article/view/8 https://jmb.tums.ac.ir/index.php/jmb/article/download/8/6