Control of Persistent Salmonella enterica on Foods with Prior Exposure to Sub-lethal Food Production-related Stresses Using a Hurdle Concept

PI: Zhao (Jack) Chen, MS, PhD


Salmonella enterica has been linked to recent foodborne outbreaks associated with the consumption of leafy greens. Moreover, low-moisture foods like almonds have also been connected to Salmonella outbreaks, where the bacteria were found to persist in raw almonds within the production and processing environment. Foodborne pathogens, such as S. enterica, may undergo sub-lethal stresses during food production, triggering adaptive responses that render them resistant to subsequent food sanitation processes.


The primary objective of this study is to develop and validate an effective non-thermal processing technology to mitigate the presence of sub-lethally stressed S. enterica on leafy greens and low-moisture foods. This research aims to provide valuable insights into the survival of sub-lethally stressed bacterial cells and how they respond to food sanitation technologies, thereby contributing to efforts to reduce the presence of persistent pathogens in food.


We have investigated 1) how sub-lethal food processing-related stresses influenced the ultraviolet-C (UV-C) resistance of Salmonella enterica on raw whole almonds (RWAs) and fresh-cut leafy greens, 2) the potential involvement of rpoS in the cross-protection of pre-stressed S. enterica against UV-C, and 3) whether Enterococcus faecium NRRL B-2354 can serve as a surrogate for S. enterica. Our results highlight the cross-protection of acid-stressed S. enterica against UV-C on RWAs and fresh-cut leafy greens, which is regulated, at least in part, by the global stress response induced by the RpoS regulon. This study also demonstrates that NRRL B-2354 can serve as a suitable surrogate by providing a margin of safety when validating UV-C treatment for inactivating S. enterica on RWAs and fresh-cut leafy greens.


This work is supported by the U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA), Agriculture and Food Research Initiative (AFRI) project [2022-67017-36541].

Journal Articles

1. Chen, Z. (2022). Application of chlorine dioxide-based hurdle technology to improve microbial food safety–A review. International Journal of Food Microbiology, 109848.

2. Chen, Z. & Meng, J. (2021). Persistence of Salmonella enterica and Enterococcus faecium NRRL B-2354 on baby spinach subjected to temperature abuse after exposure to sub-lethal stresses. Foods, 10(9), 2141.

Poster Presentations in Scientific Meetings

1. Chen, Z., Zheng, J., Micallef, S.A., Meng, J. Influence of sub-lethal food processing-related stresses on the ultraviolet-C resistance of Salmonella enterica and Enterococcus faecium NRRL B-2354 on raw whole almonds. International Association for Food Protection Annual Meeting, Toronto, Canada, 07/2023.

2. Chen, Z. Control of persistent Salmonella enterica on foods with prior exposure to sub-lethal food production-related stresses using a hurdle concept. USDA-NIFA Food Safety and Defense Project Director’s Meeting, Toronto, Canada, 07/2023.