Agriculture Reference
In-Depth Information
(Diez - Gonzalez and others 1998 ; Keener and others 2004 ). A signifi cant number of
animals may be asymptomatic carriers of enteric pathogens but shedding the organ-
isms in feces (Meng and others 2001). As a primary reservoir of
E. coli
O157:H7,
cattle, especially weaned calves and heifers, shed this microorganism intermittently
with events lasting 2 to 4 months (Zhao and others 1995). The populations of
E. coli
O157:H7 ranged from enrichment positive to 10
5
CFU/g feces. Epidemiological
surveys revealed the prevalence of
E. coli
O157 in feces from less than 6% to 28%
depending on seasons, geographic locations, and herds (Hancock and others 1994;
Zhao and others 1995; Elder and others 2000). Dietary change has also been shown
to affect fecal excretion patterns of
E. coli
O157:H7 in cattle and sheep (Kudva and
others 1995; Diez-Gonzalez and others 1998). A recent study suggests that the use of
dried distillers' grain as feed additive may contribute to the higher prevalence of
E.
coli
O157 in cattle (Jacob and others 2008). The authors hypothesized that the
decreased starch in the feed may alter the ecology in the rumen and favor the growth
of
E. coli
O157:H7.
The populations of
Salmonella
spp. have been detected in amounts up to 10
7
CFU/g
in feces of healthy animals (Pell 1997; Himathongkham and others 1999).
Campylobacter
spp. is present in poultry wastes, and average populations have been
reported to be near 10
5
CFU/g in feces (Stern and Robach 2003 ).
Persistence of Enteric Pathogens in Preharvest Environment
In Animal Feces and Slurry
The intestinal tracts of animals are the natural habitats for enteric pathogens.
Immediately after being defecated in feces, these pathogens are exposed to a hostile
environment with numerous microorganisms, from both animals and the environment,
to compete for nutrients. Studies have demonstrated that some enteric pathogens such
as
E. coli
O157:H7 and
L. monocytogenes
were still able to multiply for ca. 1
3 logs
CFU/g in fresh feces within 2-3 days at warm temperatures, followed by steady
decline in bacterial populations during storage (Wang and others 1996; Himathongkham
and Riemann 1999). Even under fi eld conditions, both indicator bacteria and
Salmonella
multiplied initially for ca. 1.5 logs in bovine feces on pasture (Sinton and others 2007;
Van Kessel and others 2007). Therefore, in order to eliminate pathogens from feces
effectively, the initial treatment of feces should be emphasized.
During storage, exponential inactivation of enteric pathogens in feces was reported
in several studies. When stored at various temperatures,
E. coli
O157:H7 and
S
.
Typhimurium were inactivated in cattle manure following a fi rst - order reaction with
most rapid die-off at 37 °C (Wang and others 1996; Himathongkham and others 1999).
The survival of other serotypes of shiga-toxin producing
E. coli
(STEC) such as O26
and O111 in naturally infected cow feces ranged from 1 to 18 weeks with extended
survival at 15 °C (Fukushima and others 1999). Prolonged survival of
E. coli
O157:H7
was observed in manure heaps for up to 47 days, 4 months, and 21 months, in bovine,
aerated ovine, and nonaerated ovine manure, respectively (Kudva and others 1998).
L.
monocytogenes
survived in pig manure, soil, and cattle manure for 3
∼
8
weeks, respectively, at 15 °C (van Renterghem and others 1991). When compared with
cattle manure, high ammonia content (0.2-0.4%) and alkaline pH (8.6) in poultry
∼
4, 6
∼
8, and 6
∼
