(443g) Wiggling of Motile Bacteria in Dilute, Low-Re Flows Near Walls

The dynamics of motile bacteria ultimately determine the growth of biofilms and hence, the beginning stages of many types of infectious diseases. Bacteria dynamics in dense systems have been widely studied: collective motion leads to the initiation of biofilms, which grow as a result of quorum sensing, a complex, non-equilibrium process. However, less attention has been paid to precursors of the dense bacterial suspensions that lead to biofilm formation. In this experimental study, we measure the dynamics of e. coli swimming in low Re flows through a square duct. The bacteria have been stressed by sub-MIC antibiotics, resulting in an elongated shape. The elongated bacteria wiggle as they swim with the flow, bending both concave-upward and concave-downward with respect to the fluid velocity. We track their trajectories, orientations, and the oscillation of their bending. At low flow rates, bacteria are free to swim across the channel, while at higher flow rates they exhibit a preference for trajectories aimed toward the channel wall. In either case they can be observed turning upstream near the wall, trying to swim against the flow. Analysis of their bending motion suggests a higher frequency, lower amplitude oscillation at higher flow rates, suggesting a dependence of the bending modulus on the local shear. Our results lend insight into the precursors of biofilms that may form in channel flows, such as in medical or surgical tubing. A better understanding of these precursors may inform preventive techniques for antibiotic-resistant infections that persist in hospital settings.