Biofilm formation on surfaces used for food processing under varying hydrodynamic shear stresses and biofilm removal using mechanical and chemical stressors

Abstract

Biofilms formed by pathogenic bacteria are complex communities adhering to surfaces, exhibiting increased resistance to disinfectants, thus leading to serious infections. Chemical disinfectants have long been utilized to eliminate pathogenic biofilms. Despite their potency and reliability, preliminary research suggests chemical disinfectants do not consistently achieve complete biofilm eradication. This PhD dissertation research focuses on investigating the factors governing biofilm formation and removal from food contact surfaces, such as identifying whether eithersurface roughness, kurtosis, or skewness promotes biofilm formation or if any of these factors provide additional protection against chemical disinfectants. Three research topics are included in this dissertation. The first topic is based on biofilm formation of pathogenic bacteria E. coli O157:H7, L. monocytogenes as a single species biofilm and in the presence of a non-pathogenic promoter bacterium R. insidiosa in a Centers for Disease Control and Prevention (CDC) bioreactor. Materials commonly used for food processing such as SS 316L, PTFE, EPDM, and Polycarbonate are used to grow biofilms at different shear stresses. The results from this study indicate that when E. coli O157:H7 biofilms are formed at low shear stress of 0.368 N/m2, the development is significantly heightened on surfaces with high kurtosis. This study underlines the importance of commonly sidelined surface parameters such as kurtosis. Our second research topic focuses on biofilm removal ability using chlorine from SS 316L, PTFE, and EPDM at a concentration up to 500 ppm for an exposure of 1 and 4 minutes at a flow of 1.2 liters per minute. Post-chlorine treatment, we observed that lower bacterial populations from L. monocytogenes biofilms were present in multispecies environment on PTFE material (high surface roughness), compared to SS 316L (low surface roughness) when these biofilms were grown at high shear stress of 2.462 N/m2. The third topic of this dissertation focuses on the biofilm removal using a more environmentally friendly chemical disinfectant Peroxyacetic acid to remove biofilms. When E. coli O157:H7 biofilms were formed in a multispecies environment at high shear stress and treated with peroxyacetic acid, removing biofilms from EPDM was found to be more challenging.