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Bacteria under external stress can reveal unexpected emergent phenotypes. We show that the intensely studied bacteriumEscherichia colican transform into long, highly motile helical filaments poized at a torsional buckling criticality when exposed to minimum inhibitory concentrations of several antibiotics. While the highly motile helices are physically either right- or left-handed, the motile helices always rotate with a right-handed angular velocity$\overrightarrow{\omega }$, which points in the same direction as the translational velocity${\overrightarrow{v}}_T$of the helix. Furthermore, these helical cells do not swim by a “run and tumble” but rather synchronously flip their spin$\overrightarrow{\omega }$and thus translational velocity—backing up rather than tumbling. By increasing the translational persistence length, these dynamics give rise to an effective diffusion coefficient up to 20 times that of a normalE. colicell. Finally, we propose an evolutionary mechanism for this phenotype’s emergence whereby the increased effective diffusivity provides a fitness advantage in allowing filamentous cells to more readily escape regions of high external stress.