  Optical tweezers are a technique in which microscopic-sized particles,
including living cells and bacteria, can be non-intrusively trapped with high
accuracy solely using focused light. The technique has therefore become a
powerful tool in the field of biophysics. Optical tweezers thereby provide
outstanding manipulation possibilities of cells as well as semi-transparent
materials, both non-invasively and non-destructively, in biological systems. In
addition, optical tweezers can measure minute forces (< 10-12 N), probe
molecular interactions and their energy landscapes, and apply both static and
dynamic forces in biological systems in a controlled manner. The assessment of
intermolecular forces with force measuring optical tweezers, and thereby the
biomechanical structure of biological objects, has therefore considerably
facilitated our understanding of interactions and structures of biological
systems. Adhesive bacterial organelles, so called pili, mediate adhesion to
host cells and are therefore crucial for the initial bacterial-cell contact.
Thus, they serve as an important virulence factor. The investigation of pili,
both their biogenesis and their expected in vivo properties, brings information
that can be of importance for the design of new drugs to prevent bacterial
infections, which is crucial in the era of increased bacterial resistance
towards antibiotics. In this thesis, an experimental setup of a force measuring
optical tweezers system and the results of a number of biomechanical
investigations of adhesive bacterial organelles are presented. Force measuring
optical tweezers have been used to characterize three different types of
adhesive organelles under various conditions, P, type 1, and S pili, which all
are expressed by uropathogenic Escherichia coli. A quantitative biophysical
force-extension model, built upon the structure and force response, has been
developed.
