Persistence and Control of Foodborne Pathogens in Hydroponic Systems

Commodities

• Vegetables: greens (leafy), greens (lettuces)

Practices

• Production Systems: hydroponics

Hydroponic farming continues to grow in popularity. Recent
outbreaks linked to hydroponic produce highlight the need for
improved understanding of how foodborne pathogens persist in
these systems and provide a way to control them. The aim of this
proposal is to (i) study the persistence of
Salmonella, E. coli, and Listeria, in two types
of hydroponic systems (deep water culture and Kratky) and to
(ii) assess the efficacy of PAA as a pathogen
control strategy. In the first objective of this project,
pathogens will be inoculated into water to assess their
persistence. In the second objective of this project, pathogen
control interventions will be assessed to reduce food safety risk
while maintaining, or promoting, plant health and productivity. I
hypothesize that under conditions where biofilms do not form, the
Salmonella and E. coli strains will persist for
two weeks, while the Listeria strains will persist for
one week as suggested by a previous study (Ilec et al., 2022). I
also hypothesize that a treatment of 80ppm PAA for 30 minutes
will reduce pathogen load. The findings from this project will
help understand the microbial risks and how to manage them in
hydroponic farms. Findings will be disseminated among Northeast
hydroponic farmers and beyond through the Mid-Atlantic Fruit and
Vegetable Convention.

Objective 1: Evaluate the persistence of Salmonella,
E. coli and L. monocytogenes in hydroponic
systems.

Expected outcome: Characterization of
Salmonella, E. coli and Listeria persistence in
hydroponic systems in a controlled laboratory setting.

Deliverables: Spreadsheet and graphs with
concentrations of Salmonella, E. coli and L.
monocytogenes in a nutrient solution over the growing period
and the final harvested produce grown in the DWC and Kratky
hydroponic systems.

Potential pitfalls and alternative approaches:
We plan to inoculate leafy greens seeds with an inoculum at
10⁸ CFU/ml of Salmonella, E. coli and L.
monocytogenes. If this inoculum level leads to
concentrations of pathogens that are below the limit of detection
of our microbial detection methods, we will collect a larger
volume of a sample and filter it in order to obtain quantities of
pathogens.

Objective 2: Assess pathogen control steps aimed at
reducing pathogens on seeds

Expected outcome: Developed and assessed
pathogen control step for seeds that is accessible and feasible
for hydroponic farmers to implement to reduce the risk of
introducing Salmonella, E. coli and L.
monocytogenes contamination in hydroponic systems.

Deliverables: A mitigation step made publicly
available to hydroponic farmers in the NE region through a
publication and communication at the Mid-Atlantic Fruit and
Vegetable Convention.

Potential pitfalls and alternative approaches:
If the mitigation step negatively impacts seed germination, plant
growth or plant quality, we will evaluate alternative methods to
control bacterial growth. Preliminary small-scale experiments
will be conducted to assess these factors.