The bactericidal effect of a helium dielectric barrier discharge plasma jet generated in laminar (at 3 m/s) and preturbulent (at 10 m/s) helium flows is considered in terms of average discharge power and distance of treatment of Escherichia coli cells grown on a nutrient agar surface in a Petri dish. Sizes of bacteria inhibition zones are estimated and mor-phological changes in ultrastructure of bacterial cells are revealed using electron microscopy. This study suggests that the gas flow regime is an important factor in the production of the helium plasma jet used to inhibit bacteria. We reveal the different responses of E. coli cells treated by the helium plasma jet generated in laminar and preturbulent gas flows. Numerous focal destructions appear in the cells after 2 min of treatment with the laminar gas flow regime. Along with these focal destructions, expansion of cytoplasm and a superhelix of nucleoids are revealed with the preturbulent regime. We explain differences in behavior of cell morphology under the plasmajet formed at different gas flow regimes by the different gas-dynamic conditions ofmixing ambient air into the helium flow.