Biofilm Formation on the Food Contact Surfaces Under Varying Hydrodynamic Shear Stresses

Bacterial biofilms are generally found as a consortium of multispecies organisms. Biofilms growing on food contact surfaces can be a public health hazard if the contaminated surfaces are not effectively treated with antimicrobials. In the food processing plants, these microorganisms are found in various places and equipment surfaces, such as in the drains, storage vessels, tanks, conveyor belts, pipelines, pipe fittings. Biofilm growth and morphology is affected by various factors such as fluid hydrodynamics and food contact surface properties to name a few. Therefore, it is important to understand biofilm formation on different equipment surfaces under laminar and turbulent flow conditions.

In our research, we are performing a comparative multispecies biofilm study using an annular reactor (CDC bioreactor) and a parallel flow bioreactor characterized by shear stress possessing different flow hydrodynamics. The multispecies biofilm will be formed by using a pathogenic bacteria and a non-pathogenic bacteria, environmental isolates of Escherichia coli O157:H7 and promotor strain Ralstonia insidiosa, respectively.

Stainless steel, polycarbonate, and other surfaces with varying hydrophobicity can be used in the study.  We are using SS 316L, Ethylene propylene diene monomer (EPDM) and Polycarbonate (PC) coupons in these bioreactors. The information obtained on biofilm formation on various surfaces at different flow characteristics would be imperative in developing effective disinfection strategies in biofilm removals in laboratory and plant processing environments  

We will be growing the biofilms in the CDC bioreactor under the shear stresses τ = 0.0128, 0.0431, 0.1449 N/m², these shear stresses correspond to a turbulent flow regime. For the parallel flow bioreactor, we will be growing the biofilms under laminar and turbulent flow regimes, the shear stresses for a parallel bioreactor will be 0.084 N/m² ,1 N/m² and the shear stress in turbulent region will be 12.9 N/m². We will determine loosely and strongly attached bacterial populations of E. coli O157:H7 and R. insidiosa in biofilm by selective plating on MacConkey agar with sorbitol  (SMAC) and Tryptic soy agar with select antibiotics, respectively. The experiment will be performed for all the coupons retrieved from the CDC bioreactor and the parallel flow reactor for all the shear stress that they are subjected to for biofilm formation. Measuring the bacterial population would enable us to determine the effects of different shear stresses, flow hydrodynamics and different types of surfaces on multispecies biofilms. It can also allow us to investigate if there is a relationship between the hydrophobicity and surface topography with the formation of multispecies biofilm. Bacterial growth will be plotted for non-pathogenic Ralstonia insidiosa and Shiga toxigenic Escherichia coli biofilms, formed on stainless steel SS316L, polycarbonate (PC) and EPDM surfaces. The bacterial growth will be calculated across all the shear stresses induced in the CDC bioreactor and the parallel flow bioreactor. Overall the aim of our work is to study the influence of hydrodynamics in biofilm growth, the role of mechanical stresses and chemical disinfectants on the multispecies biofilm removal.