Agriculture Reference
In-Depth Information
newly introduced cultures may not represent the natural fi tness of enteric pathogens
in feces. A few studies investigated the survival of naturally occurring
E. coli
O157 in sheep feces and cowpats on pasture, and raw cattle manure on garden
soil. The survival of the pathogens ranged from 30 days to 15 weeks (Ogden
and others 2002; Mukherjee and others 2006; Van Kessel and others 2007). Due
to the uneven distribution of pathogens in the fecal samples collected, the results
may not be suitable to validate the previous pathogen survival studies in manure-
amended soil.
Current studies reveal that the length of pathogen persistence in manure-amended
soil varied from a few days to more than 300 days, which is likely attributed to varia-
tion in types of wastes and environmental parameters used by different studies.
Therefore, any recommendations of the land application of manure need to be based
on studies that examined a wide range of organic wastes under various environmental
conditions (Avery and others 2005 ).
Pathogen Contamination on Fresh Produce Fertilized with Manure
and Compost
Major sources of fresh fruit and vegetable contamination on the farm include feces,
raw manure, or inadequately treated compost, soil, irrigation water, water used for
fungicides and insecticide applications, dust, wild animals, and human handling
(Beuchat and Ryu 1997; Doyle and Erickson 2008).
Enteric pathogens can survive in feces and manure-amended soil for extended
periods of time, which may serve as the potential inoculum onto plants in the fi eld.
Both plant surfaces and the roots are the locations where pathogens can possibly grow
or survive (Brandl 2006). The phyllosphere of plants is considered as a hostile
environment for enteric microorganisms due to temperature fl uctuations, low water
activity, limitation in nutrients, and UV radiation, whereas the rhizosphere of plants
provides a moist and low oxygen tension environment with large numbers of micro-
organisms and organic nutrients (Brandl 2006).
The plant pathogens contaminate produce by splashing onto the leaves when heavy
rain or water-gun irrigation occurs, being internalized from roots and other openings
of the plants, imbedding into phylloplane biofi lms, and adhering to the roots via soil
particles (Fett 2000; Heaton and Jones 2008). Growing evidence has demonstrated
that enteropathogenic bacteria, fi tted for the intestinal habitat, have the ability to colo-
nize the entire plant including roots, fl owers, and seeds (Guo and others 2002; Brandl
2006). Application of raw manure, compost, or irrigation water containing enteric
pathogens facilitates the movement of enteric pathogens from animal feces to the
phyllosphere and the rhizosphere of plants in the fi eld.
Recently, considerable research efforts have been focused on the pathogen persis-
tence in vegetables grown in soil fertilized with animal manure or compost, or irrigated
with contaminated water (Natvig and others 2002; Islam and others 2004a-d, 2005).
These studies were conducted either under controlled environments such as growth
chambers or greenhouses, or in fi elds by examining various factors such as types of
vegetables, time of pathogen introduction, soil type, pathogen inoculation levels, and
different weather conditions.
