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

2. Bacterial Hazards Associated with Swine Manure
storm drains, and one in the City of Lethbridge. The
percentage of samples positive for Salmonella averaged
16.7% with no AMU, 20.0% with low AMU, 11.4% with
medium AMU, 33.0% with high AMU, 52.5% for the
storm drains, and 4.6% in Lethbridge. E. coli O157:H7positive
samples averaged 10.1% with no AMU, 0% with
low AMU, 3.8% with medium AMU, 0% with high
AMU, 0% for the storm drains, and 9.1% in Lethbridge.
No direct correlation between bacterial prevalence and
manure production was identified, and the authors
postulated that factors influencing bacterial runoff
as well as time, amount, and frequency of manure
applications may have influenced the surface water
contamination for these pathogens (Johnson et al. 2003).
Pathogenic bacteria may have survival mechanisms in
water similar to the nematodes in soil. Signoretto and
associates (2004) found, during an 18-mo survey of
lake and seawater, that Enterococcus faecalis was either
attached to plankton or free in water, but not both in
lake water; and in seawater, most cells were attached to
plankton rather than in the water. In a follow-up study,
attachment of Enterococcus faecalis to plankton induced
the viable but nonculturable state, indicative of an
undetected bacterial reservoir (Signoretto et al. 2005).
In river water inoculated with different Salmonella
strains and held at room temperature, direct counts
of the bacteria did not change over a 45 day period,
even though plate counts (on Trypticase Soy Agar
plates) of the bacteria decreased of from 10 8 to 10 3
CFU/ml untreated river water, although 1 strain
decreased to about 10 CFU/ml (Santo Domingo,
Harmon, and Bennett 2000). This finding illustrates a
caveat: evaluations of bacteria using culture methods
potentially can underestimate the load of pathogens in
a given sample, because the bacteria can enter a state in
which they are not cultured by the standard methods.
Rollins and Colwell (1986) reported a similar condition
in Camplylobacter jejuni where the bacterium, which
had been inoculated into stream water and held at
4°C, was not detected using plate counts after 10 d but
viable campylobacters were sustained for over 4 mo
at concentrations similar to the original inoculum. A
number of factors seem to be involved in the survival of
Campylobacter species in water including temperatures
below 16°C and the degree of oxygenation (Buswell
et al. 1998). These authors also demonstrated that
incorporation into biofilms doubled Campylobacter
survival times.
Su M M a r y
Determining the environmental fate of bacterial
pathogens from swine manure is extremely difficult.
Biological variables include pathogen shedding by
individual pigs; microbial interactions within stored
manure; inoculation of stored manure each time a pig
sheds pathogens; interactions with plants, nematodes,
organic matter, and soil microorganisms after land
application; and water organic matter, aquatic plants,
and plankton. Physical variables include type of manure
storage, temperature and humidity during storage, soil
type, temperature, moisture, water pH, salinity, and
rainfall events (Table 2.2). Fecal shedding of pathogens
has been the aspect of this topic that has been most
studied, yet understanding still is limited. Although
some research indicates that pathogens in swine manure
do not survive long once they are applied to the soil,
other data contradicts this with relatively long survival
times in soil and water. There is a great need for good
hypothesis-driven research to determine the factors that
affect the environmental survival and persistence of
zoonotic pathogens contained in swine manures.
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