Agriculture Reference
In-Depth Information
manure was considered an important factor in rapid inactivation of
Salmonella
,
E. coli
O157, and
L. monocytogenes
(Himathongkham and Riemann 1999). Reduction in
water activity of feces apparently is another factor for pathogen inactivation (Wang and
others 1996; Himathongkham and others 1999). These results indicate the potential for
a robust population of pathogenic bacteria in manure, especially cattle manure, during
storage and a potential vehicle for transmitting the pathogens to animals, food, and the
environment. Himathongkham and others (1999), based on their research fi ndings,
recommended that cow manure should be held for 105 days at 4 °C or 45 days at 37 °C
to achieve a 5-log
10
reduction of both
E. coli
O157:H7 and
S.
Typhimurium.
It is a most common practice on dairy farms to wash animal feces, urine, and feed
debris into a slurry mixture, which is then held in a settling lagoon undergoing aerobic
or anaerobic degradation for a period of time before disposal (Meyer and others 1997).
During storage, both
E. coli
O157:H7 and
S
. Typhimurium had initial growth at 20
and 37 °C followed by population decline with decimal reduction times ranging from
2 days to 5 weeks in manure slurry (Himathongkham and others 1999). Fast pathogen
reduction was observed when storage temperature was at 37°C. Two other studies
reported a faster population decline of
E. coli
O157:H7 in cattle manure slurry than
in solid manure at temperatures below 23°C, suggesting the infl uence of solids in
slurries on the pathogen survival (Maule 1999; Kudva and others 1998). In addition
to many studies on
E. coli
O157:H7, the fate of STEC O26 was investigated in cow
slurry (Fremaux and others 2007b). The pathogen survived for at least 88 days in cow
slurry without any genetic change.
In Manure-Amended Soil
Animal wastes in the form of raw or composted manure are routinely applied to the
agricultural land as a fertilizer for the crops and soil amendment. Application of
organic wastes can increase plant nutrients and organic matter and enhance the bio-
logical, chemical, and physical attributes of soil (Bulluck and others 2002; Gagliardi
and Karns 2002). However, if not properly applied or disposed of, animal waste can
leach out of the soil or be transported by runoff to pollute the water sources and the
environment (Gagliardi and Karns 2000). Most importantly, the application of manure
and manure slurries contaminated with enteric pathogens to soil provides an opportu-
nity for pathogens to contaminate produce, drinking water, and irrigation water.
When animal manure is incorporated into the soil, the antagonistic effect of soil
microorganisms and the hostile environment of soil microcosm are likely factors in
killing enteric bacteria. Properties of soil such as soil composition and texture, indig-
enous soil microorganisms, protozoal grazing, pH, water activity, oxidation-reduction
potential, presence of a rhizosphere and microbial interactions can infl uence the sur-
vival or inactivation of pathogenic bacteria (Fenlon and others 2000; Brimecombe and
others 2007 ). Under fi eld conditions, other variables, such as solar radiation, tempera-
ture fl uctuation, manure types, manure application rates, and desiccation, may also
affect the persistence of enteric pathogens (Jones 1999).
Effect of Soil Temperature on the Persistence of Enteric Pathogens
Microbial activities are affected by the temperature to which the microorganisms are
exposed. For example,
E. coli
O157:H7 survived in manure-amended sandy loam soil
