Food Protection Trends - September/October 2022 - 364

tested for pathogenic E. coli, 11% were positive for STEC and
8% were positive for E. coli O157:H7 specifically. The highest
E. coli O157:H7 prevalence was in water samples collected
close to or downstream from cow-calf cattle operations. Of
1,405 water samples tested for S. enterica and L. monocytogenes,
65 and 43%, respectively, were positive. Twenty-four of the
survey's 30 sampling sites were Salmonella positive 70 to 90%
of the time, and some serotypes persisted over several years.
(The watershed sources sampled in that study (32) are not
used for produce production in the study region.) Benjamin
et al. (11) collected samples from eight cow-calf ranches
in Monterey, San Benito, and San Luis Obispo counties in
California from June 2008 through late October 2010. Three
of 204 surface water samples and 1 of 93 sediment samples
were positive for E. coli O157. In approximately the same
time frame, Benjamin et al. (10) collected agricultural water
samples from streams and ponds near or on leafy greens farms
in the California Central Coast area and reported that >15%
(n = 437) were positive for E. coli O157 and 6% (n = 96) were
positive for Salmonella.
Earlier surveys of California water sources also produced
similar findings. In Monterey and San Benito counties, 7.1%
of water samples (n = 252) collected from May 2008 through
June 2009 were positive for S. enterica (51). Starting in January
2005 and continuing through August 2006, Cooley et al. (29)
sampled 22 locations in watersheds in the same area on 23 occasions
for E. coli O157 prevalence. Over the 19-month study
period, the group reported a 12.8% prevalence for an accumulated
584 samples taken at 1-month intervals. In a similar study,
the same group (31) collected >13,000 samples from water,
cattle, multiple species of wildlife, produce, and soil at multiple
California Central Coast farms and identified E. coli O157 and
non-O157 STEC at various prevalences, illustrating some of
the potential transport systems in this region.
Another recent study was conducted to investigate the
prevalence of STEC-specific bacteriophages in water samples
collected in 20 watersheds throughout the produce-growing
areas of the Salinas Valley (California) and found the 13
(9.9%) of 131 samples contained bacteriophages that were
lytic against STEC strains, including serogroups O45, O145,
O157, and O179 (81). Researchers at Cornell University
(Ithaca, NY) sampled water (n = 74) from produce-growing
region watersheds in New York and reported that 11%
were positive for Salmonella and 30% were positive for L.
monocytogenes (128). In a more recent study, the same research
group reported a strong association between ruminant and
human fecal source-tracking markers and Salmonella isolation
and detection of STEC genes (eaeA and stx) associated with
pathogenicity in agricultural water samples collected from
68 upstate New York streams between April and October
2018 (138). Antaki et al. (2) sampled irrigation water for
three growing seasons on three farms in a mixed producegrowing
region of southern Georgia. Ten percent of surface
water samples (n = 39) and 13.6% of subsurface samples
364 Food Protection Trends September/October
(n = 44) from two farm ponds were positive for Salmonella.
Salmonella was also found sporadically in water samples from
farm ponds on Virginia's eastern shore, with 19% prevalence
in both 2015 and 2016 (n = 200) (133). In Oldman River
Basin, southern Alberta (Canada), Campylobacter, Salmonella,
and the swine-specific Bacteroides marker detection rates were
significantly higher in water that was downstream from areas
where livestock density was greatest than in water upstream
from those areas (70). These study results reveal the variation
in microbial quality of environmental and agricultural water
sources in the North American continent.
Another microbiological aspect of agricultural water
investigated by researchers is the release of microorganisms
into the atmosphere via mechanical mechanisms. Bacteria
attached to water droplets can be released from water bodies
and become airborne. Droplets produced by mechanisms such
as bubble bursting and fragmentation are transported into the
atmosphere by wind, with many of the small droplets traveling
over long distances (1, 107). This phenomenon may be
pertinent to lagoons located at concentrated animal operations.
Droplets may be released from lagoons that are mechanically
aerated, when it rains, and when effluent is added. A recent
study documented the transfer of microorganisms in soil
by microdroplets created by rainfall impingement. The
microdroplets are transported immediately by wind or over
potentially long distances after movement to the atmosphere
(72). However, as noted by Ravva et al. (112), large volumes
of contaminated aerosolized droplets would be required for
pathogenic bacteria to pose a food safety risk to crops grown
downwind of a microdroplet source.
Airborne particulate pathways
The question of whether pathogens associated with
airborne particulates from concentrated animal operations
and biosolid or manure spreading can cause disease in humans
when inhaled has been explored by researchers over the past
decades (66, 112, 131, 146). However, the role that aerosols,
airborne dust, and particulates in general play in pathogen
dispersion to produce-growing environments has been grossly
understudied (36, 116). Bacteria use various mechanisms such
as surface charge, weak molecular forces, cell hydrophobicity,
and substances and structures on their membranes to attach
to aerosols and go wherever the wind may carry them (36,
41, 72). Numerous studies have been conducted to measure
bacteria, including human pathogens, in aerosols such as dust
samples (26, 29, 41, 72, 87, 103, 110, 116, 130, 136, 145).
Researchers have also studied transmission of microorganisms
associated with airborne particulates produced by livestock
and poultry operations in particular (13, 40, 116, 131, 146).
E. coli strains captured downwind from a swine house and
dairy farm were closely related to those strains detected in feces
and air within the pig and dairy facilities (40, 116). Thiel et al.
(131) found that manure applied and incorporated into fields
also can become airborne and that bacteria attached to dried
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