Growth of Escherichia coli O157:H7, Non-O157 Shiga Toxin–Producing Escherichia coli, and Salmonella in Water and Hydroponic Fertilizer Solutions

Abstract

The desire for local, fresh produce year round is driving the growth of hydroponic growing systems in the United States. Many food crops, such as leafy greens and culinary herbs, grown within hydroponics systems have their root systems submerged in recirculating nutrient-dense fertilizer solutions from planting through harvest. If a foodborne pathogen were introduced into this water system, the risk of contamination to the entire crop would be high. Hence, this study was designed to determine whether Escherichia coli O157:H7, non-O157 Shiga toxin-producing E. coli , and Salmonella were able to survive and reproduce in two common hydroponic fertilizer solutions and in water or whether the bacteria would be killed or suppressed by the fertilizer solutions. All the pathogens grew by 1 to 6 log CFU/ml over a 24-h period, depending on the solution. E. coli O157:H7 reached higher levels in the fertilizer solution with plants (3.12 log CFU/ml), whereas non-O157 Shiga toxin-producing E. coli and Salmonella reached higher levels in the fertilizer solution without plants (1.36 to 3.77 log CFU/ml). The foodborne pathogens evaluated here survived for 24 h in the fertilizer solution, and populations grew more rapidly in these solutions than in plain water. Therefore, human pathogens entering the fertilizer solution tanks in hydroponic systems would be expected to rapidly propagate and spread throughout the system and potentially contaminate the entire crop.

Comparative microbial analyses of hydroponic versus in-soil grown Romaine lettuce obtained at retail

“…Greenhouse cultivation, which includes hydroponically grown produce, is reported as safer from microbiological issues compared to other farming practices due to reduction of risk factors including soil ( Holvoet et al., 2015 ; Sirsat and Neal, 2013 ). However, hydroponic systems can become contaminated with pathogens from water, substrates, and human activity ( Moriarty et al., 2019 ; Shaw et al., 2016 ). For instance, the Food and Drug Administration released a report of a multi-state salmonellosis outbreak associated with a hydroponic farm that led to 31 illnesses and 4 hospitalizations in 2021.…”

Total Coliform and Generic E. coli Levels, and Salmonella Presence in Eight Experimental Aquaponics and Hydroponics Systems: A Brief Report Highlighting Exploratory Data

“…Although relatively few studies have investigated the prevalence and distribution of food safety hazards in aquaponics systems, these systems are of increasing interest as a way to address food sustainability and security needs. Studies conducted in conventional and greenhouse production environments, and fish supply chains indicate that multiple pathways exist for the introduction of foodborne pathogens into hydroponic and aquaponic systems, including, but not limited to, fish feed, fish waste, the system's water, and the vegetable seeds [3,[23][24][25][26][27][28][29][30][31][32]. Due to the limited number of studies that investigated food safety hazards in aquaponics or hydroponics systems [27,[32][33][34][35], additional prevalence data are needed to fully characterize and manage food safety hazards associated with various aquaponics and hydroponics inputs.…”

Sources of food contamination in a closed hydroponic system

“…Hydroponic production may reduce this risk, as the growing media has little to no contact with the edible portion (Settanni et al 2013). Although the use of hydroponic growing systems all but eliminates transfer of microbes from wildlife and soil, Salmonella, Escherichia coli O157:H7, human noroviruses and Listeria monocytogenes have been identified on hydroponic produce (Solomon et al 2002;Lopez-Galvez et al 2014;Shaw et al 2016). Several theories accounting for the microbial presence on foods produced by the hydroponic system have been developed, though the exact mechanisms of pathogen introduction are largely unknown (Strayer 1994;Ge et al 2014;Allende and Monaghan 2015;Lopez-galvez et al 2016).…”