Download Effect of Nitric oxide on biofilm formation by Escherichia coli

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