Impact of surface topography and hydrodynamic flow conditions on single and multispecies biofilm formation by Escherichia coli O157:H7 and Listeria monocytogenes in presence of promotor bacteria

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Biofilm formation of E. coli O157:H7 and L. monocytogenes in the presence of promotor bacteria R. insidiosa was evaluated on equipment surfaces under different hydrodynamic flow conditions in a Centers for Disease Control and Prevention biofilm reactor (CBR). The CBR containing 330 ml bacterial suspension (6 log CFU/ml in 10% TSB) was used to grow the biofilms on SS 316 L, PTFE, Polycarbonate and EPDM rubber surface coupons under 100, 200 and 300 rpm (shear stresses 0.368, 1.218 and 2.462 N/m2, respectively) for 24 h in batch flow and additional 24 h in continuous flow conditions. Surface roughness and topography of coupons were measured by electron microscopy. Bacterial populations in biofilms were determined by scrapping of coupon surfaces and plating on selective media. Multispecies E. coli O157:H7 biofilm formations were affected by the surface and shear stress. SS, PTFE, and PC exhibited a significant increased biofilm growth at higher shear stress of 2.462 N/m2 compared to 0.368 N/m2. Multispecies L. monocytogenes biofilms formation decreased with increasing shear stress on all the surface materials. Our study emphasizes the importance of surface skewness and kurtosis besides surface's roughness while selecting the material for food processing environments.