Abstract
Food safety concerns have been raised over vegetables and herbs grown in aquaponics and hydroponics due to the reuse of wastewater and spent nutrient solutions. This study was conducted to determine the occurrence of foodborne pathogens in greenhouse-based aquaponic and hydroponic systems. Fish feces, recirculating water, roots, and the edible portions of lettuce, basil, and tomato were collected at harvest, and microbiological analyses were conducted for the bacterial pathogens Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes, and Salmonella spp. Enrichments and selective media were used for the isolation, and presumptive positive colonies were confirmed by PCR. STEC was found in fish feces, in the water of both systems, and on the surface of the roots of lettuce, basil, and tomato regardless of the system. However, contaminated water did not lead to the internalization of STEC into the roots, leaves, and/or fruit of the plants. Meanwhile, L. monocytogenes and Salmonella spp. were not present in any samples examined. Our results demonstrated that there are potential food safety hazards for fresh produce grown in aquaponic and hydroponic production systems.
Highlights
The average dissolved oxygen (DO) level was significantly lower in aquaponics (6 mg/L) than in hydroponics (10 mg/L), it was maintained at full saturation in both systems
The fish feces or human activities were demonstrated as potential sources of contamination with Shiga toxin-producing E. coli (STEC), our results showed that these were not the major sources of contamination for L. monocytogenes, and the production practices employed in this study were not associated with the risk of contamination with L. monocytogenes in either system
This study demonstrated that there is a potential risk of pathogen contamination in fresh produce grown in indoor aquaponic and hydroponic systems
Summary
Food safety has become an important issue in fresh produce production worldwide due to many factors such as importation of fresh produce from various countries, potential sources of bacterial pathogens from the growing environment, and inappropriate domestic food preparation [1,2].Nearly 48% of foodborne outbreaks are linked to the consumption of fresh fruits and vegetables [3].The apparent number of outbreaks associated with Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. has increased in recent years [4,5] largely due to improved detection methods and traceback procedures following an outbreak [6,7,8].In the United States, the Centers for Disease Control and Prevention (CDC) estimates that one in six people experience a foodborne illness every year [9]. 48% of foodborne outbreaks are linked to the consumption of fresh fruits and vegetables [3]. The apparent number of outbreaks associated with Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. has increased in recent years [4,5] largely due to improved detection methods and traceback procedures following an outbreak [6,7,8]. Outbreaks caused by E. coli O157:H7, L. monocytogenes, and Salmonella spp. were responsible for 4241 hospitalizations (82%) and 117 deaths (82%) [10]. According to a recently released annual summary from FDOSS [11], fruit and vegetable crops were in the top five pathogen-category pairs resulting in outbreak-associated illnesses in 2017, and 32 outbreaks (14%), 919 illnesses (25%), and 205 hospitalizations (51%) were associated with vegetables. Shiga toxin-producing E. coli (STEC) were responsible for 110 illnesses
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