  One striking feature of bacterial motion is their ability to swim upstream
along corners and crevices, by leveraging hydrodynamic interactions. This
motion through anatomic ducts or medical devices might be at the origin of
serious infections. However, it remains unclear how bacteria can maintain
persistent upstream motion while exhibiting run-and-tumble dynamics. Here we
demonstrate that E. coli can travel upstream in microfluidic devices over
distances of 15 millimeters in times as short as 15 minutes. Using a stochastic
model relating the run times to the time bacteria spend on surfaces, we
quantitatively reproduce the evolution of the contamination profiles when
considering a broad distribution of run times. Interestingly, the experimental
data cannot be reproduced using the usually accepted exponential distribution
of run times. Our study demonstrates that the run-and-tumble statistics
determine macroscopic bacterial transport properties. This effect, that we name
"super-contamination", could explain the fast onset of some life-threatening
medical emergencies.
