Before revision:  We use the probability density function (PDF) of turn angles, measured on tumbling E. coli wild-type {\it  , to build a Langevin equation for the deflection of the bacterial body swimming in isotropic media.
After revision:  We use the probability density function (PDF) of turn angles, measured on tumbling E. coli wild-type {\it E. coli , to build a Langevin equation for the deflection of the bacterial body swimming in isotropic media.