The study tested aquaponic lettuce and water from Ithaca College's aquaponics system against conventionally grown lettuce to compare microbial safety. Samples were tested for generic E. coli, E. coli O157:H7, and Salmonella. Results showed all aquaponic samples had acceptable E. coli levels below standards, while one store-bought sample exceeded standards. All samples tested negative for E. coli O157:H7 except one tilapia that tested positive for Salmonella, likely from human contact. Overall, the aquaponic produce and water showed lower microbial risks than conventional soil-grown lettuce, though larger studies are needed to make definitive conclusions about food safety.

1. Introduction
Though aquaponic food production is increasingly gaining popularity in the United States as a sustainable
agricultural method, there is little research focused on the microbial safety of aquaponically grown produce
(Sirsat and Neal, 2013, p. 488). Aquaponics combines aquaculture (raising aquatic animals such as fish) and
hydroponics (cultivating plants in water). Fish are raised in a tank connected to grow beds holding plants. Fish
excrete waste products in the form of ammonia (NH3) that, through natural bacterial processes, are converted
into nitrates (NO3
-) utilized by the plants for growth. The plants then purify the effluent and return it back to
the aquaculture system (Hollyer et al., 2009, p. 1).
Due to the proximity of harvested plants to fish waste, pathogen contamination of aquaponics
produce is a concern to consumers, despite the fact that fish are cold-blooded, and thus are believed to
be incapable of hosting pathogens (Alanis and Fitzsimmons, 2011). However, human maintenance of
aquaponic systems may introduce pathogens to the system. Typically the fish – including their gills, skin, and
digestive system – mimic the water in which they live, such that any pathogens living within their environment
will most likely reside in them too (Alanis and Fitzsimmons, 2011). Previous studies have found the existence
of enteric bacteria, such as Escherichia coli (E. coli), Clostridium botulinum, and Salmonella in aquaculture
systems (Alanis and Fitzsimmons, 2011). Though usually found at levels too low to be significant, studies
have also identified indigenous bacteria, including Vibrio cholerae, Vibrio parahämolyticus, Vibrio
vulnificus, Listeria monocytogenes, Clostridium botulinum and Aeromonas hydrophila, that live in a natural
aquatic environment and may be harmful to humans (Feldhusen, 2000, p. 1652). Thus, aquaponic safety
should be addressed and tests must be conducted throughout all aspects of an aquaponic system.
The Microbial Safety of Aquaponic Produce:
A Comparative Analysis of Pathogen Presence in Conventional Soil Systems
Stephanie McCulloch-B.S. Environmental Science, 2016
Department of Environmental Science, Ithaca College
Chambers, G. (2004). Aquaponics and Food Safety. Retrieved from http://www.fastonline.org/images/manuals/Aquaculture/Aquaponic_Information/Aquaponics_and_Food_Safety.pdf., Feldhusen, F. (2000). The role of seafood in bacterial foodborne diseases. Microbes and Infection, 2(2000), 1651-1660., Food Standards Australia New Zealand. (2001). Guidelines for the
microbiological examination of ready-to-eat foods. Retrieved from http://www.foodstandards.gov.au/publications/documents/Guidelines%20for%20Micro%20exam.pdf., Fox, B. K., Tamaru, C.S., Hollyer, J., Castro, L.F., Fonseca, J.M., Jay-Russell, M., and Low, T. (2012). A Preliminary Study of Microbial Water Quality Related to Food Safety in Recirculating Aqupaonic Fish
and Vegetable Production Systems. Food Safety and Technology, 51, 1-11. Retrieved from http://www.ctahr.hawaii.edu/oc/freepubs/pdf/FST51.pdf., Hollyer, J., Tamaru, C., Riggs, A., Linger-Bowen, R., Howerton, R., Okimoto, D., Castro, L., Ron, T., Fox, B.K., Troegner, V., and Martinez, G. (2009). On-Farm Food Safety: Aqauponics. Food Safety and Technology, 38, 1-7.
Retrieved from http://www.ctahr.hawaii.edu/oc/freepubs/pdf/fst-38.pdf., International Commission on Microbiological Specification for Foods. (1986). Microorganisms in Foods 2: Sampling for Microbiological Analysis: Principles and Specific Applications is the only comprehensive publication on statistically based sampling plans for foods. (2nd ed.). Toronto: University
of Toronto Press. Retrieved from http://www.icmsf.org/pdf/icmsf2.pdf., Sirsat, A. Sujata and Neal, J.A. (2013). Microbial Profile of Soil-Free versus In-Soil Lettuce Grown and Intervention Methodologies to Combat Pathogen Surrogates and Spoilage Microorganisms on Lettuce. Foods, 2(4), 488-498. Retrieved from http://www.mdpi.com/2304-8158/2/4/488.
References
The purpose of this study is to test the
hypothesis that aquaponic produce is safe for
consumption by examining the microbial quality
of aquaponic lettuce, Lactuca sativa, in
comparison to conventional soil-grown lettuce.
Because E. coli often resides in the intestines of
warm-blooded animals, this bacterium is typically
used as an indication of food and water quality for
human health (Fox et al., 2012, p. 1). Therefore,
testing for the presence of this bacterium in an
aquaponics system, along with pathogenic E. coli
O157:H7 and Salmonella, will help determine the
safety of this food production system.
Purpose
Methods
Discussion
The results showed that all the samples tested had generic E. coli counts that are
of marginal concern or risk to humans. Guidelines set by Australia and New
Zealand, and used as reference by the USDA, claim that counts less than 3 CFU/g
are satisfactory and counts greater than 100 CFU/g are unsatisfactory for
consumption of ready-to-eat foods (Food Standards Australia New Zealand, 2001,
p. 6). Thus, all samples analyzed have generic E. coli counts most likely safe for
consumption. However, due to the fact that one store bought sample contained 70
CFU/g of E. coli, there is reason to believe that aquaponically-grown produce
presents less of a food safety risk to consumers than soil-grown produce.
Nonetheless, due to the minimal number of samples tested, no definitive conclusion
about this result can be made. Additionally, there is good reason to be concerned
about the positive result of Salmonella in the tilapia. It is very possible that human
contact with the fish resulted in Salmonella contamination of the tilapia (Feldhusen,
2000, p. 1657). Ultimately, because of the small sample size, further studies should
be conducted to confirm the food safety of aquaponic produce, but the above results
suggest that at least the produce and water of Ithaca College’s CNS aquaponics
system are safe for human consumption. Overall, the results of this study can be
utilized to inform producers, consumers, and the community about food safety risks
associated with aquaponically-grown produce and convince larger purchase
programs to take advantage of aquaponic system produce.
To assess aquaponic food safety, lettuce grown in IC’s CNS aquaponics system and
lettuce purchased from an independent vendor practicing conventional methods was
analyzed for counts of general E. coli and the presence or absence of E. coli O157:H7 and
Salmonella. A full tray of organic lettuce seeds was started mid-February, and once the
lettuce reached the seedling stage, it was transplanted to the aquaponics system. The
lettuce plants grew in the system for roughly three weeks before they were harvested (Fig.
2). Using sterile gloves, twenty-five gram samples of lettuce, water, and tilapia tissue were
collected and immediately placed in plastic Ziploc bags and glass tubes. Conventional
soil-grown packaged lettuce was purchased from a local supermarket. Five samples of the
aquaponic lettuce, five samples of the store bought lettuce, three samples of the fish tissue,
and three samples of the aquaponic water were sent to an accredited microbiology
laboratory, Eurofins, for analysis. Eurofins utilized Polymerase Chain Reaction (PCR)
methods to detect for the presence of E. coli O157:H7 and Salmonella, and Association of
Analytical Chemists (AOAC) methods to count general E. coli.
Results
Sample E. coli CFU/g or ml
Aquaponic Lettuce 1 <10
Aquaponic Lettuce 2 <10
Aquaponic Lettuce 3 <10
Store Bought Lettuce 1 70
Store Bought Lettuce 2 <10
Store Bought Lettuce 3 <10
Tilapia 1 <10
Water 1 <1
Sample E. coli O157:H7 25g or 25ml
Aquaponic Lettuce 4 Negative
Store Bought Lettuce 4 Negative
Tilapia 2 Negative
Water 2 Negative
Table 1. A summary of E. coli counts from Ithaca College’s CNS
aquaponic system produce, water, and harvested tilapia as well as
from conventional-soil grown produce.
Sample Salmonella 25 g or 25 ml
Aquaponic Lettuce 5 Negative
Store Bought Lettuce 5 Negative
Tilapia 3 Positive
Water 3 Negative
Table 2. A summary of the aquaponic and conventional-soil grown
supplements tested for the pathogenic bacteria E. coli O157:H7.
Table 3. A summary of the aquaponic and conventional-soil
grown supplements tested for the pathogenic bacteria Salmonella.
All aquaponic system samples were found to have less than
10 colony forming units per gram of sample (CFU/g) (Table 1).
Except for one sample of store bought lettuce, all samples had
fewer than 10 CFU/g of generic E. coli, a level deemed
marginally acceptable by United States Department of
Agriculture (USDA) standards for ready-to-eat foods (Food
Standards Australia New Zealand, 2001, p. 6). With the
exception of one sample, all samples tested negative for the
presence of E. coli O157:H7 and Salmonella (Tables 2 and 3).
One sample of tilapia resulted in a positive test, and thus would
be unsafe for human consumption (ICSMF, 1986, p. 191).
Fig 2. The aquaponic lettuce grown for microbial testing in Ithaca
College’s CNS.Fig 1. A tilapia harvested for testing.
Fig 3. The aquaponic system in Ithaca
College’s CNS.
Acknowledgements
This project was supported by
Ithaca College’s ENVS
Student Career Development
Research Grant. A special
thank you to Ithaca College’s
aquaponics research team as
well as our faculty supervisor
Paula Turkon.