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Effect of Nitric oxide on biofilm formation by Escherichia coli Saiful Islam Urinary tract infections (UTI) are a serious health problem affecting millions of people throughout the world. Women are more vulnerable to UTI and 40 to 50% of women have faced a urinary tract infection at least once. Uropathogenic E. coli (UPEC) is the most common causative agent of UTI. Bacteria able to produce disease are called pathogenic bacteria. An important reason for treatment failure in UTI against pathogenic bacteria is the formation of catheter-related biofilm formation. Biofilms are very complex and organized communities, that help to protect bacteria from the host defences. If the patient keeps a urinary catheter for 30 days or longer, catheter-associated infections will commonly develop. Uropathogenic E. coli (UPEC) are the most common causative agent of UTI. UPEC bind to the catheter, replicate very rapidly and form biofilm. UTI causes significant medical expenditure that more than a billion dollars each year only in United States. It is now a very costly and stressful procedure to replace the infected implant or fight the infection with antibiotics, the only existing treatment against the biofilmproducing infection. Biofilm-based treatment cost is increasing rapidly every year. To reduce the cost of treatment is one of the major goals of scientist, at least those dealing with infectious medicine. The first defence against bacterial infection is the immune system you were born with. Nitric oxide (NO) contributes to this early response by its bacterial killing activity. NO is a highly diffusible molecule which broadly acts as a signal molecule in biological systems. The aim of my project was to see the effect of NO on biofilm formation by different pathogenic E. coli strains. Therefore, NO could be used as treatment against biofilm mediated diseases in future. Two nitric oxide donors, Sodium Nitroprusside Dihydrate (SNP) and DETA NONOate were used through out this study to see the effect on biofilm formation. I found that NO had a clear inhibitory role against biofilm formation by curli (a proteinaceous cell surface structure) and a major component of the outer surface of E. coli. The flu+ (encoded antigen 43 protein) gene also had an important role in biofilm formation in E. coli and I found that NO significantly inhibited the biofilm formation by the bacterial strains that formed biofilm through this pathway, using a laboratory strain that expressed the flu gene from a plasmid (an extra-chromosomal DNA molecule separate from the chromosomal DNA). Biofilm formation in all cases was inhibited by nanomolar and micromolar ranges of DETA and nanomolar ranges of SNP. Millimolar concentration of DETA and micromolar concentration of SNP inhibited both biofilm formation and bacterial growth. In nanomolar and micromolar concentration of DETA and in nanomolar concentration of SNP, bacterial growth of these strains was not significantly effected. Further studies to be needed to pinpoint the concentration of DETA & SNP that acts against biofilm formation and to possible interaction of NO with other components of immune response before using NO as treatment against biofilm related infectious diseases. Degree project in biology spring 2008 Examensarbete i biologi, 10 p Division of Clinical Microbiology, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet Supervisor: Petra Luthje Ph.D