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Title: Resistance of Listeria monocytogenes biofilms to sanitizing agents in a simulated food processing environment

item Breidt, Frederick

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2006
Publication Date: 12/1/2006
Citation: Pan Y, Breidt F, Kathariou S. 2006. Resistance of Listeria monocytogenes in biofilms to sanitizing agents and starvation in a simulated food processing environment. Appl Environ Microbiol 72 (12):7711-7717

Interpretive Summary: We describe the changes in resistance to cleaning agents and starvation by a disease causing microorganism. This microorganism, Listeria monocytogenes can be a problem in processed foods, including some minimally processed and acidified vegetable products, according to previous research. The organism can cause abortions in pregnant women, and can cause illness and death. To understand how environmental stresses affect survival of this microorganism, a simulated food processing system was set up. While this manuscript primarily addresses environmental stresses, this simulated food processing system has been shown to be a useful system for studying growth and survival of Listeria under conditions simulating real world food processing plants, including vegetable processing facilities that produce products that are not heated prior to consumption. Future studies focusing on bacterial competition between lactic acid bacteria (also present on fresh vegetables) and Listeria may be possible using the techniques developed in this work.

Technical Abstract: The objective of this study was to characterize the biofilm behavior of Listeria monocytogenes in an experimental ecosystem. Biofilms were initially formed on Stainless steel and Teflon® coupons using a five-strain mixture of L. monocytogenes. The coupons were then subjected to repeated 24-h daily cycles. Each cycle consisted of three sequential steps: (i) a brief (60 sec.) exposure of the coupons to a sanitizing agent (MatrixxTM or water as a control treatment); (ii) drying and storage of the coupons in plastic tubes for 15 h; (iii) incubation of the coupons in diluted medium for 8 h. This regimen was repeated daily for up to three weeks, and was designed to represent a simulated food processing (SFP) environment. The bacteria in biofilms were reduced in numbers during the first week of the SFP regimen, for both the control (without sanitizing agent) and MatrixxTM treatments, but then adapted to the stressful conditions and grew. Resistance to sanitizing agents (MatrixxTM, Multi-QuatTM, and chlorine) increased for bacteria in biofilms that were repeatedly exposed to MatrixxTM but not for bacteria in the SFP control biofilms. However, cells resuspended from the treated SFP biofilms and the control SFP biofilms were not significantly different in their resistance to sanitizing agents. The data suggest that the treated SFP biofilms as a whole, but not the individual cell in the biofilm, had enhanced resistance to sanitizers, possibly due to attributes in the biofilm structure or components resulting from the MatrixxTM treatments.