Pseudomonas sp. biofilm development on fresh-cut food equipment surfaces – a growth curve – fitting approach to building a comprehensive tool for studying surface contamination dynamics

The capacity of two primary growth models to describe Pseudomonas fluorescens and Pseu- domonas grimontii biofilms’ development was assessed. The Baranyi and the ‘Logistic with Breaking Delay’ models were applied for biofilms grown in various laboratory and pilot-plant devices, including pipes or mock-ups mimicking vegetables washing tanks in the fresh-cut food industry. An initial short transitional period not described by the growth models was observed during which cells rapidly attached to pilot-plant devices’ surfaces. The following observed surface contamination growth patterns were consistent with both growth models. However, only the Baranyi model was relevant to the occurrence of wide variability and/or growth curves with no lag or stationary phases. Both surface design and hydrodynamics in pilot-plant devices strongly influenced biofilm growth curves. Based on fitted parame- ters, it was possible to differentiate between areas and relate these to design parameters such as sharp corners, welds or specific hydrodynamics as 2D, 3D or near-static flow condi- tions. 15–25 h lag phases reflecting equilibrium between cell attachment and release were observed for wall shear stresses exceeding 0.5 Pa under dynamic flow conditions. Conse- quently, flow pattern design improvements by increasing the shear rate would greatly reduce food cross-contamination risk, as cleaning operations could start before any significant biofilm developments