Food Protection Trends - November/December 2024 - 402

controlled and addressed in CEA agriculture. Additionally,
in January of 2024, a recall of CEA (specifically greenhouse)
grown prepackaged salads was reported due to possible
contamination with Listeria monocytogenes (27). A positive
result for L. monocytogenes was identified during routine
product testing. At the time in which this paper was written,
no illnesses have been reported. Another microbial hazard
that would need to be addressed (due to its presence in a
wide range of sources, including natural environments), at
a minimum, is enterohemorrhagic Escherichia coli (EHEC).
Supporting the range of possible food safety hazards in
produce, Salmonella, E. coli O157:H7, human noroviruses
and L. monocytogenes have all been identified on hydroponic
produce (43, 50, 59). While prevalence studies of foodborne
pathogens have been performed in the production
environment of open fields, as well as packinghouses and
the processing environment of fresh-cut facilities (5, 13,
64), more research to systematically assess food safety risks
in the growing and harvesting of leafy greens under CEA
systems is needed.
In addition to known foodborne pathogens, it also needs
to be considered that pathogens that are not typically considered
foodborne, as well as unknown pathogens, could be
transmitted through CEA grown crops. Of special concern
are emerging waterborne hazards (e.g., Legionella) that may
be present in various water sources, which might be applied
in CEA systems (40). Particularly relevant is the recirculation
of the nutrient solution in the hydroponic system.
Water sources, such as municipal water, reclaimed water, and
surface water, present differing levels of associated microbial
risks, as each source varies in treatments and testing requirements,
with municipal water typically considered the lowest
risk (33). Additionally, irrigation distribution networks could
affect the water's microbial quality. For example, intermittent
water supply (akin to the ebb and flow hydroponic technique)
in India was found to have higher total coliform and
E. coli counts at taps compared to levels taken from taps supplied
with constant water (41). Whether the system or equipment
is temporarily or permanently assembled, the methods
by which water storage, delivery, and distribution systems are
cleaned, maintained, and stored are crucial. Given the range
of possible microbial contaminants possible in CEA, more
specific research clearly identifying microbial hazards and
their frequency is needed for the CEA sector.
While growing media for hydroponics, aeroponics,
aquaponics or soil-based growing systems vary widely and
can provide avenues for contamination of final product,
there is still limited research that would help with an
assessment of risks associated with different inputs. Nutrient
solutions, non-synthetic fertilizers (fish emulsion, algal
extracts, liquid green waste extract), and non-soil growth
media such as coconut coir or perlite are all examples
of inputs used in CEA. Different CEA systems typically
have specific requirements for handling of inputs to avoid
402 Food Protection Trends November/December
cross-contamination. Notably, CEA that integrates fish
(aquaponics) has a potential source of fecal contamination
built into the production system. While there is some
research regarding plant pathogens in soilless inputs (12,
16, 44, 61), there is little research regarding the human
pathogenic prevalence of CEA inputs. One study (18),
illustrated the role of substrates as a potential source of
contamination in hydroponic systems, which can facilitate
microbial transfer to harvested leaves. Similarly, Işık et al.
(39) found that growth media used in soilless microgreen
production can affect the transfer of pathogens to edible
and inedible portions of microgreens. Due to the lack of
knowledge surrounding the microbial environment of these
inputs, combined with the wide range of inputs used and the
different systems they are used in, there is a large knowledge
gap regarding human pathogen microbial risks from risks
from inputs and how inputs inputs facilitate the spread to
edible or inedible portions of products (37).
While automated systems can control seeding, planting,
moving plants, irrigation (e.g., timed release and dosing of
water and nutrients), harvesting, and post-harvest processing
(e.g., moving growing trays pulled along a series of chains
and pulleys, packing), these automated systems are often not
hygienically designed or created with sanitation/disassembly
in mind. This, combined with year-round production and
limited sanitation (e.g., once a year), increases the potential
risk of persistence and spread of pathogens. In addition,
complex equipment and infrastructure in CEA may require
extensive and well-managed maintenance to minimize food
safety risks. In vertical farms, there are permanent structures
with multiple growing levels. Equipment associated with
growing includes multiple levels using shelving systems or
vertically mounted growing systems (e.g., growing troughs
suspended from the ceiling) and vertical conveyor systems
(23). Relevant to vertical farms, if any of the top layers
become contaminated, there is a high likelihood that it could
disperse via water droplets onto lower levels and onto edible
portions of plants. Future research and development on
hygienic design and sanitation in CEA facilities (including
validation and verification) thus would be valuable (37).
An additional challenge associated with microbial
food safety in CEA is that there is limited knowledge
of the microbiome within a CEA facility compared to a
traditional agriculture microbiome. Plant microbiomes
have been reported as playing important roles in securing
food production and reducing microbial food safety risks
(11). For example, sensitivity to invasion by pathogens can
be characterized by different states of plant microbiomes,
i.e., the ones that are in dysbiosis and therefore sensitive to
pathogen invasion vs. the ones that are in eubiosis and more
resilient to microbial perturbations (7).
Microbial interconnectivity between ecosystems plays an
important role in the development of plant microbiomes
and microorganisms can be transmitted via the internal
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