Fate and Transport of Zoonotic Bacterial, Viral, and - The Pork Store ...

2. Bacterial Hazards Associated with Swine Manure
Little research has been published on the load of
potentially pathogenic E. coli in swine feces and stored
manure. When 33 samples were taken from swine
manure handling systems on farms across 7 states,
100% of samples were positive for STII toxin gene from
enterotoxigenic Escherichia coli when at least 35 isolates
were screened (Khatib, Tsai, and Olson 2003). Samples
from 5 pig manure lagoons were evaluated for the
frequency of enterotoxigenic and enterohemorrhagic
toxin-associated genotypes of E. coli (Chern, Tsai, and
Olson 2004). All pig manure samples were positive for
STII toxin gene (associated with enterotoxigenic E. coli),
with a frequency range of 1 gene per E. coli to 1 gene per
33 E. coli (Chern, Tsai, and Olson 2004). Additional
assessment of the presence of genes associated with
pathogenic E. coli in feces and wastes would be
beneficial, inasmuch as E. coli remains one of the
predominant indicator organisms isolated from swine
manure, and information regarding the proportion
of isolates that may represent human pathogenesis is
relevant to determining potential human risks.
Few studies have assessed the presence of zoonotic
pathogens in stored swine manure. When pig manure
slurries from 54 farms were surveyed, 22% were positive
for Salmonella and 24% were positive for EPEC (Jones et
al. 1976). At least 10 Salmonella serovars were isolated,
and pathogen concentrations were approximately
10 3 bacteria/milliliter (ml). Hill and Sobsey (2003)
consistently detected Salmonella at four of four swine
farms investigated in North Carolina, at concentrations
of 2.2 to 2.4 log10 MPN/100 ml in flushed swine
lagoon liquid. Reductions of 1 to 2 log10 (90 to 99%)
in Salmonella concentrations were measured for each
swine lagoon used to treat the flushed swine manure.
Anugwa and colleagues (1989) recovered Campylobacter
at an average of 2 x 10 6 cells/g feces, dry weight, and
Enterobacteriaceae at 5 x 106 cells/g feces, dry weight.
Hutchison and colleagues (2005a) investigated the
prevalence of zoonotic pathogens in farm wastes in
Britain. One hundred eighty-four pig manure samples
(126 fresh and 58 stored) were tested between 2000
and 2003 and evaluated for E. coli O157, Salmonella,
Listeria, and Campylobacter. Pathogens were detected
in pig manure samples as follows: 11.9 and 15.5% were
positive for E. coli O157; 7.9 and 5.2% for Salmonella;
19.8 and 19.0% for pathogenic Listeria; and 13.5 and
10.3% for Campylobacter, in fresh and stored manure,
respectively (Hutchison et al. 2005a). Manure samples
from 13 piggeries in Queensland, Australia, were
sampled and examined for thermotolerant coliforms:
E. coli, Camplylobacter jejuni, C. coli, and Salmonella
(Chinivasagama et al. 2004).
In general, the closer to the animals the waste
effluent was, the higher the level of pathogens.
Salmonella detection was relatively low; only three
farms had counts higher than 11 MPN/100 ml. All
farms were positive for Campylobacter, with counts
ranging from less than 30 to 1.1 × 10 4 MPN/100 ml in
anaerobic lagoons following screen removal of manure
solids. Counts of thermotolerant coliforms and E. coli
in lagoons were higher and averaged between 10 5 to 10 6
colony-forming units (CFU)/100 ml (Chinivasagama
et al. 2004). Van Renterghem and colleagues (1991)
reported 16% of fresh pig feces were positive for Listeria
monocytogenes, but it was not detected in stored
manure slurries. In a survey of enterococci presence
in four European countries (Sweden, Denmark,
Spain, and England) 97% of pig manure samples
were found positive for enterococci (both pathogenic
and nonpathogenic species), and colony counts were
between 10 4 and 10 5 CFU/ml (Kühn et al. 2003).
Much of the data on the persistence of pathogens
in swine manure are limited by modeling pathogen
survival in a static system. Most research on persistence
of pathogens in manure and wastewaters removes the
manure from on-farm storage, adds a specific number
of pathogenic bacterial cells, and then monitors the
concentration of pathogenic bacteria in the manure
over time. There is evidence that pathogens do not
exhibit the same survival properties under controlled
laboratory conditions; in fact, survival times in the
laboratory may be decreased compared with field
conditions (Rogers and Haines 2005). Furthermore,
manure storage and treatment on-farm is a dynamic
system with continual inoculation of fresh feces
and urine; therefore, more research is needed to
study pathogen survival in continuous, dynamic
manure treatment processes. Chern, Tsai, and Olson
(2004) speculated that the difference in occurrence
of enterotoxigenic genes in swine manure between
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