Alternating electric fields induce a period-dependent motion of Escherichia coli in three-dimension near a conductive surface.

Abstract

It has been demonstrated that electric fields can minimize surface adhesion of bacteria, but how they affect the near-surface bacterial dynamics has remained largely overlooked. In the present study, the three-dimensional motions of Escherichia coli (E. coli) HCB1 and HCB1414 near a conductive surface under alternating-current (AC) electric fields were monitored with digital holographic microscopy. The period (T) of AC fields exhibited profound effects on near-surface bacterial behavioral patterns and thus affected the surface adhesiveness of E. coli. When T ≥ 1 s, HCB1 cells tumble frequently, and both two strain cells increasingly undergo subdiffusive motions compared to the case without electric fields. The bacterial density near the surface varies due to galvanotaxis depending on the initial polarization of the surface. For shorter periods (T ≤ 0.1 s), the electric fields reduce the near-surface bacterial density by 10%-20% with the surface as either an anode or a cathode. The AC fields directly disturb the intrinsic bacterial rotation. The bacterial body exhibits strong wobbling at T ≥ 1 s. Such wobbling was suppressed with decreasing T, which reduces the collisions between E. coli and the surface and thus leads to declining bacterial density. These results suggest that the use of low-density AC fields with tunable T may be a promising antifouling strategy and merits further investigations.