Elahe Tasallot Maraghi - Department of Microbiology, School of Biology, College of Science, University of Tehran
N Kashef - Department of Microbiology, School of Biology, College of Science, University of Tehran

Background and Objectives: Biofilm formation by Staphylococcus aureus is a serious concern in treatment of diseases and medical industries. Biofilm is a group of microorganisms that grow on living and non-living surfaces and surrounded by an extracellular matrix to provide an important barrier against the antibiotic therapies and immune system defense. This study aimed to determine the ability of biofilm formation in standard and clinical strains of S.aureus. Materials and Methods: Assessment of biofilm formation was performed on polystyrene flat – bottomed microtitre plates using the crystal violet (CV) staining assay.After removing the dye solution and washing with water, the attached dye was solubilized with 10% acetic acid and the optical density at 490 nm was determined by a microtitre plate reader.A biofilm-positive phenotype was defined as an optical density at 490 nm of ≥ 0.17. Results: To interpret the biofilm results, the isolates were classified as follows: non-producing, weak, moderate and strong-producing, based on the optical density (OD) average values. S.aureus (ATCC25923) and 9 clinical isolates were strong biofilm producers and one clinical isolate was a moderate-biofilm producer(UTMC1451). Conclusion: All the examined strains had the ability to form biofilms and the majority of them produced a thick biofilm.