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This paper presents a method for measuring the mechanical response of flagella on a single Escherichia coli cell to chemotactic agents using a microfabricated gold-coated silicon nitride cantilever. Changes in flagella motion on the cell immobilized near the free end of the cantilever due to changes in the chemical environment are sensed by a shift in resonance frequency (1st flexural-mode) of the cantilever. The thermally excited resonance frequency of the cantilever is measured using PicoPlusreg AFM liquid cell setup, by focusing the laser on the back of the cantilever. The cantilever with the cell immobilized on it when immersed in leucine solution, an E. coli chemo-attractant, is observed to an increase the frequency by 0.69%. This is due to increase in tensile stress on the cantilever leading to spring stiffening, as a result of stimulated flagellar motion of the cell attached to the top. Thus the flagellar response of single-cell E. coli to chemotactic agents can be quantified.