Biofilms S143 microorganisms evade host defences and are resistant to systemic and local antibiotic therapy. Biofilms have been implicated in dental and periodontal diseases, chronic tonsilitis, otitis media. We demonstrated that bacterial biofilms are present in patients with chronic rhinosinusitis (CRS). Although many etiological factors contributing to CRS have been described, the role of bacteria is not well definied. Methods: We reviewed 9 cases of CRS patients using culturing methods, scanning (SEM) and transmission (SEM) electron microscopes. The patients were undergoing functional endoscopic sinus surgery (FESS) or radical antrostomy performed because of failure of past medical therapy. Mucosal specimens and sinus lavage were taken from diseased maxillary sinuses and cultured on media for aerobic and anaerobic bacteria and fungi. Microrganisms were identified by conventional biochemical tests. The samples were prepared using standard methods for SEM and TEM. Areas of interest were photographed. Results: Bacterial biofilms observed under electron microscope were detected in 3 patients. Cultures of these specimens contained: Streptococ- cus spp., Escherichia coli, Klebsiella pneumoniae, Streptococcus agalac- tiae, Proteus mirabilis. In 2 patients neither bacteria nor fungi were present (negative culture and microscopy). In the samples of 4 patients Gram-negative rods, alpha-haemolytic streptococci, Propionibacterium spp. and Corynebacterium spp. were identified. However no biofilm-like structures were observed under electron microscope. Conclusion: Biofilms were demonstrated to be present in patients un- dergoing surgery for CRS. This is one of not numerous documentations of biofilms in association to chronic rhinosinusitis. P612 Characterisation of bacterial isolates colonising urinary tract catheters X. Wang, I. Ehren, H. Lunsdorf, A. Fruth, U. R¨ omling, A. Brauner (Stockholm, SE; Braunschweig, Wernigerode, DE) Objectives: To characterise biofilm and related behaviours of bacteria colonising urine catheters and urine. Methods: Bacterial isolates were recovered and species identified from urine and urinary catheters samples of 45 patients. All isolates were characterised for biofilm formation and related behaviour such as expression of extracellular matrix components. Serotype was assayed. Catheter samples were investigated by electron microscopy to analyse biofilm formation. Results: In total 179 bacterial isolates was recovered from urine catheter samples. Most commonly recovered species were coagulase negative staphylococci (CNS), Enterococcus faecalis, Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. Catheter recovered E. coli isolates were significantly more prevalent in patients with prostatic cancer than patients suffering prostatic hyperplasia. Catheter recovered CNS isolates were significantly more prevalent in patients with short-term catheterisation than those with long-term and more prevalence than S. aureus, E. faecalis, Streptococci, E. cloacae and Enterobacteriaceae in patients with short- term catheterisation. 96% of isolates showed biofilm formation in vitro. Isolates of P. aeruginosa demonstrated the highest biofilm formation and adherence capacity among investigated species. E. coli isolates recovered from patients with catheter associated urinary tract infection formed significantly more biofilm and adherence than E. coli isolates causing asymptomatic colonisation. E. coli isolates with UTI-related O-antigen formed significantly more biofilm and adherences than remaining isolates. E. coli isolates with H antigen adhered more and expressed more extracellular matrix than bacteria without H antigen. Conclusions: Most isolates from catheter can form biofilm in vitro. The capacities to form biofilms contribute to the virulence properties of P. aeruginosa and E. coli by enabling colonisation of the catheter. Although CNS is commonly found on catheter surfaces it is mainly retrieved during short time catheterisation, which could be due to its inability to persist urine flow and over growth of other bacterial species. The correlation found between E. coli and prostate cancer merits further investigation. P613 Influence of sub-inhibitory concentrations of antibiotics on biofilm formation by Salmonella typhimurium J. Majt´ an, L. Majt´ anov´ a, V. Majt´ an (Bratislava, SK) Objectives: Salmonella typhimurium strains are important food-borne pathogens. Numerous studies have documented the ability of Salmonella spp. to adhere and form biofilms on different surfaces. The aim of this study was to investigate and compare the effect of sub-inhibitory concentrations (sub-MICs) of antibiotics on biofilm formation by clinical S. typhimurium strains. Methods: The antibiotics used in this study were gentamicin, ciprofloxacin and cefotaxime. Biofilm-forming abilities of three clinical isolates of S. typhimurium (No. 18/06, 41/06, 53/06) in the presence of sub-MICs (1/2, 1/4, 1/8, 1/16 of the MIC value) of these antibiotics were assessed by absorbance at 570 nm of crystal violet-bound cells recovered from 96-well tissue culture plates after growth in TSB growth medium. Results: The effect of sub-MIC concetrations of antibiotics tested in biofilm formation was determined by the percentage of inhibition of biofilm formation. Each antibiotic had a different effect on biofilm inhibition according to the strain targeted. The most effective in all three strains were sub-MICs of gentamicin in whole concentration range. Sub-MICs of ciprofloxacin expressively inhibited biofilm formation by two strains (41/06 and 53/06). On the other hand cefotaxime markedly stimulated biofilm formation by strain 18/06 in whole concentration range, and by 41/06 and 53/06 strains at 1/2 of the MIC. Conclusion: These findings showed that gentamicin, ciprofloxacin and cefotaxime influenced biofilm formation by clinical S. typhimurium strains at sub-MIC concentrations. This effect was dependent on the strain and on the type of antibiotic. P614 Slime production in blood isolates of Staphylococcus aureus under various growth conditions O. Aslan, B. Aksu, F. Babacan (Istanbul, TR) Objectives: The production of biofilm represents an important virulence factor of certain strains of Staphylococcus aureus. We aimed to investigate biofilm production of blood-borne S. aureus isolates under different growth conditions. Methods: Total of 100 blood isolates of S. aureus were included to the study. All the isolates were identified as S. aureus by colony morphology, catalase and tube coagulase reactivity. Slime production of the isolates was detected by cultivation on Congo Red Agar (CRA) plates and quantitative microplate test. Four different Tryptic Soy Broth (TSB) formulas were used in microplates for testing their influence on biofilm production; standard TSB, TSB supplemented with 1% glucose, iron limited TSB (50% less than usual) and iron supplemented TSB (50% more than usual). Results: Only one isolate was detected as positive with three methods; CRA and quantitative microplate method with standard TSB and iron limited TSB. Of one hundred isolates, 8 were found positive (8%) in glucose supplemented TSB medium which were also found positive in iron limited TSB medium. In addition to these 8 isolates, 37 isolates (45%) were also determined as positive in iron limited medium, but only one isolate (1%) was detected as positive in iron supplemented TSB. Conclusion: Iron limited TSB medium might be the best approach to evaluate biofilm production of clinical S. aureus isolates. P615 Adhesion of Staphylococcus epidermidis to a modified cellulose triacetate membrane C.I. Extremina, P.L. Granja, A. Freitas da Fonseca, A.P. Fonseca (Porto, PT) Objectives: There is an increase in the use of biomedical materials in modern medicine, despite some problems resulting from this practice. A major drawback are the biomaterial-centred infections. Adhesion of