Biofilms consist of a cell-multilayer embedded in a slime matrix and they are the basis for produc-tion of polysaccharide adhesion by ica- operon-encoded enzymes is currently the best understood mechanism of biofilm development in staphylococci. The insertion sequence IS256, a mobile ele-ment frequently associated to transposons has the capacity to influence expression of the ica operon and subsequent biofilm formation by reversible insertion into the ica operon. We aimed to elucidate the role of insertion sequence IS256 in biofilm formation among various Staphylococcus aureus isolates from clinical specimens of hospitalized patients at Ankara and Hacettepe Universi-ties. A total of 207 S. aureus strains isolated between 1998 and 2004 from clinical specimens were included in the study. A total of 28 of the S. aureus isolates studied were methicillin-susceptible S. aureus (MSSA), 133 were methicillin-resistant S. aureus (MRSA), and 46 were vancomycin-interme-diate S. aureus (hetero-VISA) isolates. Genomic DNA was extracted from staphylococcal cultures and used as an amplification template with the primers in simplex PCRs for detection of biofilm genes (icaA, icaD), IS256. Of all S. aureus isolates studied 185 (89.4%) were positive for icaA, 201 (97.1%) were positive for icaD, 184 (88.9%) were positive for both whereas 18 (8.7%) strains were positive for only one of them. We found the positivity rates of biofilm genes (ica genes) among MRSA and hetero-VISA isolates were significantly higher than those among MSSA isolates (p< 0.001). IS256 positivity among MRSA and hetero-VISA isolates were also significantly higher than those among MSSA isolates (p<0.001). Biofilm genes among IS 256 positive S. aureus isolates were found significantly higher than those among IS256 negative S. aureus isolates (p<0.001). IS256 have the capacity to influence expression of the ica operon and subsequent biofilm formation.

Keywords: Biofilm, S. aureus, icaA, icaD, IS256