  The ability of uropathogenic Escherichia coli (UPEC) to cause urinary tract
infections is dependent on their ability to colonize the uroepithelium.
Infecting bacteria ascend the urethra to the bladder and then kidneys by
attaching to the uroepithelial cells via the differential expression of
adhesins. P pili are associated with pyelonephritis, the more severe infection
of the kidneys. In order to find means to treat pyelonephritis, it is therefore
of interest to investigate the properties P pili. The mechanical behavior of
individual P pili of uropathogenic Escherichia coli has recently been
investigated using optical tweezers. P pili, whose main part constitutes the
PapA rod, composed of ~1000 PapA subunits in a helical arrangement, are
distributed over the bacterial surface and mediate adhesion to host cells. We
have earlier studied P pili regarding its stretching/elongation properties
where we have found and characterized three different elongation regions, of
which one constitute an unfolding of the quaternary (helical) structure of the
PapA rod. It was shown that this unfolding takes place at an elongation
independent force of 27 pN. We have also recently performed studies on its
folding properties and shown that the unfolding/folding of the PapA rod is
completely reversible. Here we present a study of the dynamical properties of
the PapA rod. We show, among other things, that the unfolding force increases
and that the folding force decreases with the speed of unfolding and folding
respectively. Moreover, the PapA rod can be folded-unfolded a significant
number of times without loosing its characteristics, a phenomenon that is
believed to be important for the bacterium to keep close contact to the host
tissue and consequently helps the bacterium to colonize the host tissue.
