Attachment of Listeria monocytogenes and E.coli O157:H7 to surfaces is enhanced by the presence of nonviable cells remaining after treatment with bi-quat sanitizer

Scope and Method of Study: The ability of select strains of Listeria monocytogenes and E.coli O157:H7 to adhere strongly to surfaces and form biofilms has major implications in the meat industry and underscores the importance of sanitation. Sanitary disinfection of surfaces is often done with sanitizers which have a bactericidal effect on microorganisms, but may leave behind a carpet of dead cells (i.e., organic material) which may facilitate reattachment by new bacteria. Our objectives were to examine the detachment dynamics of sanitizers and detergents on strongly adherent L monocytogenes and E.coli O157:H7 biofilms by quantitative and qualitative means, and to examine whether a pre-existing debris layer (dead biofilm) facilitates the attachment of subsequent biofilm bacteria.;Findings and Conclusions: Bi-Quat sanitizer was bactericidal to bacterial cells but did not remove bacterial cells from surfaces as verified by SEM analysis and disinfectant assay. Bacterial counts recovered from the dead biofilm were 1.2 log CFU/ml higher than obtained from clean surfaces. Higher microbial counts obtained by attachment of bacteria to dead (sanitized) cell layers in comparison to clean surfaces shows the ability of organic layers to enhance re-attachment and initiate biofilm formation. These results were observed for both L monocytogenes and E.coli O157:H7. A surprising bit of information identified in our study was the length of time required to kill cells of E. coli O157:H7 within immature biofilms. The sanitation regimen most commercial processors apply does not come close to the 2 hr immersion that was utilized in our study to completely eliminate E. coli O157:H7 present in biofilms. The removal of organic debris from environmental surfaces in process environments is paramount to maintaining good sanitation and reducing the accumulation of bacterial biofilms.