Food Protection Trends - September/October 2022 - 371

animal operations are also located. Recent findings may
reinforce practices already in place, provide additional details
related to industry practices, or introduce new information
relevant to reducing contamination risks.
Cattle-focused strategies
Although controlling what happens on the land adjacent to
produce fields is generally beyond the produce growers' control,
coordinated efforts are being made to find solutions to reduce
food safety risks among fresh produce growers and neighboring
animal operations in the agricultural community. The Adjacent
Lands Subcommittee is a special subcommittee of the Leafy
Green Handlers' Marketing Agreement's Technical Committee
comprising growers, food safety experts, scientists, landowners,
and cattle ranchers. This committee has been examining ways
to better assess and mitigate risks that may be present on farms
growing leafy greens and on property located near these farms.
The Western Center for Food Safety and Security at UC Davis
held a " good neighbor " workshop exploring the livestockproduce
interface.
Vaccines, diet regiments, probiotics, colicins, and other
therapeutics that could decrease pathogenic E. coli levels, specifically
in cattle, are potential remedies being explored to reduce
infection by and transmission of this pathogen from animals to
the environment (83, 91, 115, 125). Recently, increased interest
and resources have been directed toward targeting vaccines, and
studies of various vaccination approaches are currently underway
(119, 122).
In a different approach, USDA researchers noted that when
contaminated feedlot surface materials were solarized by covering
with clear polyethylene, pathogenic E. coli was reduced in the
cattle feedlot pens, with 2.0-log reductions after 1 week to 3.0log
reductions after 6 weeks (12). Use of materials to increase
solarization in pens when they are empty could reduce pathogen
spread from contaminated surfaces to uninfected animals.
Protecting crops from dust deposition
Growers, especially those with fields of leafy greens in
proximity to animal operations, need to be aware of processes
that increase dust production and include monitoring of high
levels of dust influx as part of their food safety program. Studies
reviewed here provide evidence that pathogens can attach to
particulates and dust carried by wind and air currents, and
pathogens attached to dust particles can better survive adverse
conditions than when not attached to dust. Based on results
of the studies reviewed here and recent outbreaks of E. coli
O157:H7 infection associated with leafy greens (15, 63)
grown in a region near a massive feedlot or with frequent high
winds yielding significant dust, food safety can be improved by
an understanding of the mechanisms and trajectories of dust
emission from agricultural and livestock production systems.
Growers should be aware of dust that originates from
adjacent or nearby animal operations, but the dust from
cultivation also can be problematic. Research by Thiel
et al. (131) points to the risks of releasing pathogens in
association with particulates when cultivating contaminated
soil. Research of risk factors associated with Salmonella and
L. monocytogenes contamination in produce fields revealed
an increased likelihood of finding both pathogens in fields
that were cultivated within 7 days of soil sampling (128). In a
field adjacent to or near animal operations, restricting the last
soil cultivation to within 7 days of harvest may minimize the
potential for pathogen contamination.
Specialty crop growers are familiar with the complexity
of balancing food safety and conservation or ecological
efforts, often referred to as comanagement. The issue of
vegetation attracting wildlife to specialty crop production
sites and/or providing cover for physical hazards from human
activity is a major part of comanagement discussions (84).
A known function of trees that is not often a major part of
these discussions is that tree canopies provide protection
from airborne particulate deposition (36, 55). In the vast
open fields of the western United States, namely California
and Arizona, the two states that provide the vast majority of
U.S. leafy greens, few greenbelts with large trees have been
developed between produce fields, and most fields are not
located close to forested land. Unless studies can provide
definitive data for assessing risks from dust versus riparian or
forest environments, discouraging specialty crop production
close to greenbelts and riparian or forested areas to reduce
the opportunity for animal intrusion seems at odds with the
protection trees provide from dust.
Bacteriophages as mitigators of bacterial pathogens
Bacteriophages are viruses that infect bacteria. Because
they typically infect only one type of bacteria, bacteriophages
could be used as indicator organisms or surrogates for bacterial
presence. Because phages lyse and destroy cells after replicating
inside them, phages could also be part of novel pathogen
mitigation methods (81). In their study of bacteriophage
presence on an organic farm, Lennon et al. (79) identified and
isolated phages from goat feces, and these phages collectively
destroyed E. coli O157 and six other non-O157 STEC strains.
The authors suggested that these phages may be candidates for
biocontrol to reduce STEC presence in the farm environment.
Other researchers have isolated lysins, a type of phage enzyme
that degrades the walls of the infected bacterial cell (120).
Purified lysin can destroy cell walls of sensitive gram-negative
pathogenic bacteria such as E. coli, Salmonella, and Shigella on
contact, thus acting as an antimicrobial agent. When applied
for 10 or 20 min to a romaine leaf model contaminated with
E. coli O157:H7, 100 ppm of a novel lysin resulted in 2- and
4-log reductions of the pathogen, respectively, with no
reported visual or tactile change in lettuce quality (144).
Plant breeding
Although early in the development stage, the breeding of
plants that are more resistant to pathogen contamination is
September/October Food Protection Trends 371
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