Mostafa Shahmoradi - Department of Microbiology, Zanjan Branch, Islamic Azad University, Zanjan, Iran.
Peyman Faridifar - Department of Microbiology, Zanjan Branch, Islamic Azad University, Zanjan, Iran.
Reza Shapouri - Department of Microbiology, Zanjan Branch, Islamic Azad University, Zanjan, Iran.
Seyed Fazlollah Mousavi - Department of Microbiology, Microbial research center, Pasteur Institute of Iran, Tehran.
Mahnaz Ezzedin - Department of Microbiology, Islamic Azad University, Tehran branch, Tehran, Iran.
Bahman Mirzaei - Department of Microbiology, Islamic Azad University, Tehran branch, Tehran, Iran. & Department of Medical Microbiology and Virology Faculty of Medicine, Mazandaran University of medical sciences, Sari, Iran.

Background: Among hospitalized patients, Staphylococcus aureus (S. aureus) infections pose a serious health threat. The present study investigated the frequency of biofilm forming genes among clinical isolates S. aureus and their susceptibility to antibiotics. Methods: The clinical samples were analyzed via standard biochemical assays for identifying different bacterium, which was then confirmed using the multiplex colony PCR method. Those samples identified as S. aureus were examined for the presence of the cna, fnbA, fnbB and pvl genes. The antibiotic susceptibility of the S. aureus isolates was then tested. Results: Using the standard biochemical assay approach, 54 S. aureus strains were identified. However, when using the multiplex PCR method 50 S. aureus strains were identified among the clinical samples. The in vitro biofilm formation assays determined 3 (6%) strains of S. aureus to be strong biofilm forming, 15 (30%) of the isolates were determined to be moderate biofilm forming and, 32 (64%) were determined to be weak biofilm forming. Among the isolated strains, the specific frequencies of the biofilm forming genes were determined to be 31 (62%) for cna, 35 (70%) for fnbA, 13 (26%) for fnbB and 1 (2%) for pvl. In 11 (22%) of the isolated strains fnbA, fnbB and cna genes were all present. All strains were determined to be penicillin, amoxicillin and clavulanic acid resistant.   Conclusions: Due to the increase of the antibiotic resistance in biofilm producing S. aureus strains, rapid identification of antibiotic resistance can help to eliminate the infection effectively.

Biofilm, Multiplex colony PCR, Pertussis toxin, Spreading factors, .