A key role in bacteria surfaces contamination and biofilm development is played by cell motility and adhesion, that can be heavily dependent on flow conditions. The aim of this work is to study the influence of flow induced -shear stresses on P. fluorescens AR11 cell motility at solid-liquid interface. We quantitatively characterized cell motility during biofilm formation, using a commercial microfluidic flow cell. Flow conditions were defined by changing the imposed flow rate to mimic in our lab scale microfluidic setup stresses at the chamber walls typical of real conditions. Biofilm development in time was monitored by Time-Lapse microscopy coupled with image analysis to quantify cell motility. Persistent Random Walk models were used to analyse cells trajectories and describe bacteria motility according to Fickian (not Brownian) diffusion models. Specific attention was paid to assess statistical significance of measurements. Preliminary results suggest that mechanical stresses have a measurable effect on cell attachment and motility in biofilm, affecting system morphology.