Food Protection Trends - November/December 2019 - 577

et al. in 2008 (1), who employed different types of wash
water (such as potable, recirculated, and diluted recirculated
water) inoculated with microorganisms to study the ability
of bacteria to cross-contaminate produce. A significant
amount of transmission of E. coli from the inoculated to
the un-inoculated samples occurred during washing. It was
concluded that the contamination level may impact water
quality and the efficacy of added sanitizers for reducing the
concentration of waterborne pathogens. It was also shown
that cross-contamination of fresh-cut produce can occur
if even a small amount of contaminant is present during
washing, thus demonstrating the need for using good quality
wash water with an effective sanitizer to control or prevent
contamination (1). In 2004, Rodgers et al. compared
chemical sanitizers for inactivating E. coli O157:H7 and
L. monocytogenes on apples, lettuce, strawberries, and
cantaloupe (27). They employed ozone (3 ppm), chlorine
dioxide (3 and 5 ppm), chlorinated trisodium phosphate
(100 and 200 ppm) and peroxyacetic acid (80 ppm) with
regard to their effect on reduction of E. coli O157:H7 and
L. monocytogenes in an aqueous system. Pathogens employed
for the study were prepared by using three different strains
of each organism, resulting in a cocktail mixture prepared
at a concentration of approximately 6 log CFU/ml. Four
sanitizers were prepared at the appropriate concentrations,
using distilled water (wash water), which was also employed
as a control, at 21° and 23°C. Samples were homogenized
and plated on various media to quantify mesophilic
bacteria, E. coli O157:H7, L. monocytogenes, yeasts, and
molds. Significant reductions in both pathogens occurred,
with ozone being the most effective treatment, followed
by chlorine dioxide, chlorinated trisodium phosphate,
and peroxyacetic acid (in decreasing order of efficacy).
Quantification of organisms yielded relatively similar results
for all nine days of sampling, although toward the end of the
study, mold and yeast populations were significantly higher
for samples treated with chlorine dioxide and ozone. It was
concluded that chlorine dioxide, chlorinated trisodium
phosphate, and ozone all effectively reduced the counts of
E. coli O157:H7 and L. monocytogenes (27).
Plain water can be used for reducing the probability of
contamination during washing, but it also can transfer
pathogenic microorganisms (13). Washing fresh produce
with an effective sanitizer is therefore important to obtaining
products free of organic matter and especially to preventing
cross-contamination between clean and contaminated products. The aforementioned experiments clearly demonstrate
the importance of employing good-quality post-harvest wash
water along with a sanitizer to reduce pathogens and spoilage
organisms on fresh produce.
SOIL AND MANURE
Soil has long been known to provide essential nutrients
for the growth and development of plants (7). Soil and
manure have both played major roles in exposing plants to a

diverse array of microflora comprised of both beneficial and
harmful microorganisms. Many foodborne outbreaks have
been linked to consumption of fruits and vegetables grown
in soil contaminated with manure or polluted irrigation
water (25). Contamination of produce with improperly
treated or contaminated soil, manure, or compost on the
farm can cause pre-harvest contamination of fresh produce
(19). Although competition from natural soil flora and
unexpected environmental conditions may hinder the
growth and development of pathogens (19), the potential of
pathogens to persist and survive has led researchers to study
their ability to adapt to extreme environmental conditions.
Islam et al. in 2004 studied the fate of Salmonella enterica
serovar Typhimurium on field-grown carrots and radishes
exposed to different types of compost inoculated with the
target organism (20). The three types of compost employed
(poultry manure, dairy cattle manure, and alkaline-pHstabilized dairy cattle manure), along with irrigation water,
were inoculated with 107 and 105 CFU/ml of Salmonella.
Crops were grown in the contaminated field, and samples
were withdrawn to study the persistence of Salmonella,
which was shown to survive for an extended time and was
detectable in the soil for 203 to 231 days (20). Similar results
were observed in the case of contaminated irrigation water.
The team concluded that employing either contaminated
manure or irrigation water could play a major role in
contaminating the soil, leading to prolonged persistence of
the pathogen, which could eventually contaminate produce,
especially root vegetables (20).
Transfer of Listeria innocua from contaminated compost
and irrigation water to lettuce leaves was studied by Oliveira
et al. in 2011 (25). The objective was to determine the
transfer of the pathogen from contaminated compost and
water to the edible portion of the plants as well as the survival
of the pathogen through two seasons, fall and spring. Viable
L. innocua were retrievable from the field for up to 9 weeks, at
a concentration of 105 CFU/gdw in fall and 103 gdw (gram by
weight) in spring (25). The team was also able to successfully
demonstrate the transfer of the pathogen from contaminated
soil and water to the edible portion of the plant, especially
the outer leaves. It was concluded that the pathogen survived
better in fall than in spring, which indicates that temperature
and humidity play major roles in regulating growth of the
bacteria. In general, employing contaminated compost and
irrigation water will contribute to the presence of foodborne
pathogens on vegetables (25).
Johannessen et al. in 2005 studied the uptake of E. coli
O157:H7 from organic manure into crisphead lettuce (21).
Lettuce seedlings were planted in soil that was fertilized with
contaminated bovine manure containing 104 CFU/g of
E. coli O157:H7 and grown in a climate-controlled greenhouse for 50 days, after which samples were withdrawn
randomly and tested for the presence of the pathogen.
The pathogen was not detected on the edible portion, the
outer leaves, or the roots of the lettuce harvest, despite the
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