Agriculture Reference
In-Depth Information
addressing preharvest produce food safety issues. The confl ict involves a contradiction
between creation of vegetative zones for fi ltering runoff from fi elds and wildlife
habitat, and the perceived risks of attracting to this habitat wildlife colonized possibly
with pathogens (Berreti and Stuart 2008). Some compromise between these competing
interests will be necessary for sustaining the valuable locations where produce is
grown and improving the quality and safety of produce.
As noted above, a convergence of multiple events probably is required to cause a
major outbreak, implying that each event alone may be insuffi cient. The changes in
pathogen incidence and virulence in a preharvest food production environment can be
speculated to be associated with corresponding and dynamic changes in the biology,
ecology, hydrology, meteorology, and agricultural practices in an environment.
Considering the impossibility of controlling certain aspects of the ready- to - eat produce
production environment, it is logical to assume that additional outbreaks will occur.
Intensive practices leading to exposure of pathogens to complex environments, or
signifi cant replication of microorganisms, will increase the rates of new mutations and
fi tness in environments where mutations are benefi cial. Modern molecular biology
techniques (genomics) are facilitating the fi ngerprinting of outbreak-related pathogen
strains for purposes of high-resolution tracking of the possible sources of contamina-
tion in preharvest environments. Also, comparative genomics of these data reveal
insights about pathogen evolution and emergence of virulence-related factors that
raise questions about whether produce outbreak-related pathogens are more virulent
and have special fi tness characteristics (Zhang and others 2006; Manning and others
2008). The rapid changes possible in bacterial genomes by mutations, phage inser-
tions and deletions, and recombination, as examples, predict the emergence from
high-intensity environments (food production) of organisms with selected fi tness
characteristics that refl ect the environment. If some of these fi tness characteristics are
virulence traits in humans (i.e., pathogens), pathogens will be identifi ed through
studies of human illness.
Considering the known potential risk factors in the preharvest environment docu-
mented above, some approaches for preventing contamination of food can be offered.
Common sense approaches include maintaining water quality and minimizing expo-
sure of fi elds to wild animals, surface water (fl ooding), and dust from agricultural
activity. Other less obvious approaches requiring more resources are identifying high-
shedding livestock or wildlife, treatment of livestock with effective vaccines or other
antimicrobials, checking and maintaining feed quality, observing fi eld conditions
(wildlife intrusions), redirecting or destroying suspect produce, and controlling wild
animal habitat. Postharvest approaches involve sample testing (test and hold), clean
water, novel sanitizers (chemical or biological), and irradiation, to name a few. More
details regarding interventions will be discussed in other sections of this topic.
Finally, it should be noted again that the incidence of illness linked to contaminated
produce is quite low relative to the total number of produce consumptions. Nevertheless,
the increased incidence of outbreaks and the apparent hypervirulence of pathogen
strains associated with some of these outbreaks (Manning and others 2008), emphasize
that continued vigilance is necessary to minimize the severity of any outbreaks that
might occur. Until a highly effective and nontoxic “kill step” is developed for elimi-
nating pathogens from postharvest fresh produce, pathogens in the preharvest environ-
ment deserve our serious attention and continuing research efforts.
