Location: Food and Feed Safety Research
Title: Effect of stressors on the viability of Listeria during an in vitro cold-smoking process Authors
Submitted to: Agriculture, Food and Analytical Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2012
Publication Date: December 1, 2012
Citation: Pittman, J.R., Schmidt, T.B., Corzo, A., Callaway, T.R., Carroll, J.A., Donaldson, J.R. 2012. Effect of stressors on the viability of Listeria during an in vitro cold-smoking process. Agriculture, Food and Analytical Bacteriology. 2:195-208. Interpretive Summary: Listeria monocytogenes is a dangerous food-borne pathogen and is a frequent contaminant of the cold-smoked fish industry. By reducing the presence of this organism from this part of the food chain, human health can be improved. Five strains of Listeria were exposed to different stress conditions encountered during the cold-smoking process. Differences between virulence was correlated with these physical changes. These data suggest that differences exist in the mechanisms utilized by virulent and avirulent strains to adapt to stresses encountered in the cold-smoking process.
Technical Abstract: Listeria monocytogenes is a dangerous food-borne pathogen and is a frequent contaminant of the cold-smoked fish industry. Elimination of this bacterium from the cold-smoking processing environment requires an understanding of how this microbe tolerates the stressful conditions encountered. Therefore, the aim of this study was to determine whether exposure to stresses likely to be encountered during the cold-smoking process impacts various strains of Listeria monocytogenes and Listeria innocua differently. Five strains of L. monocytogenes (EGDe, F2365, HCC7, ATCC 15313, and HCC23) and a L. innocua strain (CLIP 11262) in exponential or stationary growth phase were sequentially exposed to conditions that mimic those found in the cold-smoking process: freeze (-20'C)-thaw (25'C), high salt, liquid smoke (phenolic compounds), and anaerobic storage at 2'C. Growth was monitored throughout the process by viable plate counts. Viability for stationary phase cells exposed to the mock cold-smoking process significantly increased for all strains except EGDe; viability also increased when cells in exponential phase were exposed to the cold-smoking process yet was not significant for EGDe- and HCC7-treated cells. The integrity of the cell envelope of HCC23 and HCC7 was also analyzed by transmission electron microscopy. The cell envelope of the avirulent strain HCC23 was affected by all treatments examined, while the cell envelope of the virulent strain HCC7 was affected only by exposure to liquid smoke and storage conditions. Results indicate that both virulent and avirulent strains in this study in either exponential or stationary phase can tolerate the stressors encountered during the cold-smoking process and that avirulent strains are significantly more resistant to these conditions than virulent strains. These data suggest that differences exist in the mechanisms utilized by virulent and avirulent strains to adapt to stresses encountered in the cold-smoking process.