Surveillance of E. coli O157:H7 and Salmonella Typhimurium in Hydroponic Systems with Nutrient Solutions of Different Electrical Conductivities

Lettuce is the most popular leafy green in the Americans diet, comprising nearly one-fifth of the $21.8 billion in vegetable and melon sales in 2022. With the objective of supplying the current and future demand of food if find different ways and techniques of production. While lettuce is traditionally grown in open field spaces, this method faces challenges in urban areas or regions with unpredictable or unfavorable weather conditions. In response, hydroponic techniques on greenhouses under Controlled Environment Agriculture (CEA) have been adopted to extend production, aiming to overcome environmental restrictions and boost land productivity to meet future food demands. This kind of production model was not extent of contamination of foodborne pathogens, causing the most recent multistate outbreak in 2021 linked to Salmonella Typhimurium. As a result, although the hydroponic industry has put several mitigation mechanisms for human pathogens, new approaches can be assessed for effectiveness within the sector. The first chapter of this thesis provide, and overview related to the CEA industry, focusing on the nutrient film technique (NFT) hydroponic technique for lettuce production, and the pathogens associated, including outbreaks, sources of contamination, E. coli and Salmonella persistence and adaptability in hydroponic environments. Furthermore, chapter 2 highlight the behavior and surveillance of Salmonella Typhimurium and E. coli O157:H7 in NFT systems under different electrical conductivities (EC) of 1.2 mS·cm⁻¹, 1.7 mS·cm⁻¹, 2.2 mS·cm⁻¹. The findings underscore no significant difference in pathogen behavior under the three electrical conductivities. After the inoculation happed a cross contamination permitted pathogen accumulation on the roots section of the crop. Both pathogens were capable to survive on the nutrient solution and root section for 28 days of lettuce production. However, they presented a different behavior with more persistent characteristics for Salmonella and a second growth stage for E. coli after day 7. Those results showed that the hydroponic conditions for the crop are better for the human pathogens at the same time, representing a risk of cross contamination of any point of production at the edible part of the crop.