Characterization of the Bacterial Pili Colonization Factor Antigen I by Optical Tweezers

Abstract: In this thesis the colonization factor antigen I (CFA/I) of the enterotoxicogenic Escherichia coli (ETEC) is characterized biophysically with an optical tweezers. ETEC is the causative agent of travellers’ diarrhoea. The CFA/I is an adherence organelle, often named pili, mediating attachment to the epithelia of the small intestine, essential for infection. An optical tweezers were used to unfold the pili showing a steady state force of about 8 pN during unfolding. Also, the force dependence on unfolding velocity was studied. At velocities above 1.75 μm/s, the force increased linearly with the logarithmic velocity, in line with results from UPEC associated E. coli. The resulting force of CFA/I differs significantly from previously studied type 1, P and S pili which are in the range 25-30 pN. This is supposed to reflect differences in the host environment, i.e. the difference between gastrointestinal and urinary tract. The general behaviour however, seem to be the same for the different pili, in accordance with the similar macromolecular structure. In addition, the steady state force of the F1C pili of Escherichia coli was estimated to 28pN.