Occurrence and transfer of pathogens from the production environment to leafy greens grown in controlled environment agriculture

Production of leafy greens in Controlled Environment Agriculture (CEA) has significantly increased over the last few years. CEA has evolved from simple shade structures and hoop houses to full indoor vertical highly sophisticated greenhouse facilities with controlled lighting, water, and ventilation. These protected systems promote the efficient production of crops in an environmentally friendly way but they are not inherently safer than open systems as contamination can occur through different production practices and procedures that introduce hazards into the environment. CEA growers have developed food safety standards and recommendation guidelines on CEA. However, these guidelines have not prevented the occurrence of foodborne illness outbreaks associated with leafy greens grown in these CEA operations. The outbreak reported by the FDA (June and August 2021), involving packaged leafy greens contaminated with Salmonella, is a recent example. Additionally, listeriosis outbreaks have been frequently linked to fresh produce. L. monocytogenes contamination from environmental sources has shown to play an important role in fresh produce contamination. However, the likelihood of L. monocytogenes persistence in CEA systems is still unknown. The current proposal aims to contribute to generating practical knowledge on potential risk sources and transmission routes of pathogen contamination in CEA, as well as suitable corrective actions for implementing disinfection strategies. To accomplish this main goal, four objectives have been identified. The first objective will improve the understanding of how different environmental factors interact and affect the probability of Salmonella spp. and L. monocytogenes contamination in different CEA facilities using a systematic sampling. This will allow the detection of potential sources of contamination. In the second objective, the application of whole genome sequencing (WGS) to the isolates found in Objective 1 will allow us to enhance our understanding of the origin, transmission pathways, and possible persistence of specific strains. Establishment of the genetic correlations of the foodborne isolates will be necessary to understand if different sources of contamination show similar or different lineages, leading to the identification of contamination routes and patterns (episodic and persistent exposures). Data will be obtained on the distribution of identical or similar WGS sequence types in different types of samples and sampling times for each CEA facility. The third objective will focus on the use of abiotic surrogates, such as DNA Barcode Abiotic Surrogate (DBAS), for the identification of potential traffic patterns from the indoor production environment to leafy greens. The fourth objective encompasses the assessment of the efficacy of practical and feasible sanitation strategies implemented in CEA facilities against Salmonella spp. and L. monocytogenes contamination. Observational studies in different CEA facilities will help to determine the efficacy of different sanitizing procedures against different types of contamination scenarios (transient and persistent). The main benefit of this project will be the acquisition of science-based knowledge to help in developing risk-based preventive measurements that fulfill current FDA requirements and recommendations for CEA growers to reduce potential hazards such as Salmonella spp. and L. monocytogenes. To characterize potential contamination patterns in CEA facilities is needed to lead the implementation of suitable corrective actions.