Most scientists as well as lay people assume, for example, that a sneeze helps clear infection, or that urine helps to clear bacteria from the urinary tract.
This may be true in some cases, but not in all. The presence of fluid force within the body, called shear stress, actually helps the bacteria that cause urinary tract infections, E. coli, to thrive. UW researchers have identified a mechanism by which the bacterial adhesion protein FimH can detect the presence of shear flow and "lock down" the bacteria on the surface being invaded. The protein, which acts as a nanometer-scale mechanical switch, senses when the force is reduced, thus giving the bacteria a chance to scurry along safely.
(A nanometer cannot be seen with the naked eye. It is one-thousandth of a micrometer; in comparison, a strand of human hair can be 50 to 100 micrometers thick.)
The simplest way to think of this is that some bacteria work like a "finger trap." The harder you pull, the harder your fingers stick in the trap. The more you move your fingers together without force, the looser the trap.
The findings are described in the June 28 issue of the journal Cell.
"E. coli has developed the ability to hold on tight only when the body fluid is trying to push it away. Just by using this finger trap-like mechanism, they're sensing the strength and direction of the flow. Bacteria will resist high forces that threaten to remove them from the surface, but might move along with a weak 'non-threatening' flow. In this way, they can move actually against the removing flow," says Dr. Evgeni Sokurenko, one of the authors and research assistant professor of microbiology in the UW School of Medicine.