Source of Article: http://westernfarmpress.com/news/foodborne-pathogens-1203/
3, 2008 10:51 AM, Mark A. Trent
Farm Advisor, Imperial
conscious consumers love the convenience of purchasing fresh, bagged
salads. Increasing demand for fresh-cut produce has reached an estimated $12
billion in annual sales with $5 billion attributed to cut, packed salad and
This increased demand also
increases the chance for foodborne illnesses to
occur. Even though millions of people eat tons of fresh-cut greens and
other vegetables each year, a single foodborne
outbreak can seriously affect the public’s confidence in our food supply
and change people’s eating habits. The cost of the 2006 E. coli outbreak in
spinach has exceeded $100 million, with sales declining more than 30
Just as understanding the
ecology of insect pests and the organisms that cause plant diseases is
crucial to crop management, knowledge of the life systems of foodborne pathogenic bacteria can help us to produce
and provide a safe and healthy product for consumers. In general, bacteria
are classified according to their genus and species.
For example, Escherichia coli
or E. coli and Salmonella enterica or S. enterica. However, because of the diversity among
certain species of bacteria it is often necessary to divide the species
further into groups known as subspecies, strains, or serovars.
For example the genus
Salmonella consists of two species, S. enterica
and S. bongori. Diversity lies in the over 2,000 serovars that comprise S. enterica.
An example of a serovar is S. typhi,
which causes systemic infections and typhoid fever. The complete
classification for S. typhi is: Salmonella enterica subsp. enterica serovar typhi.
One reason for subspecies,
strains and serovars is that a subspecies of a certain
bacterial species may or may not cause disease. Also, many subspecies, serovars or strains of a certain pathogenic bacteria
species may cause disease in one host, but not in another.
Typically, E. coli colonizes
the gastrointestinal tract of newborns within hours after birth and is the
predominant facultative anaerobe in the humans and other warm-blooded
animals’ colonic flora. Most strains of E .coli are beneficial; humans and
other species cannot survive without them.
However, some strains have evolved
to be pathogenic. Pathogenic E. coli have short, hair-like projections or
appendages called “fimbriae” on their outer
surface that act as a virulence factor by promoting adherence. In their
natural environment, pathogenic E. coli use these fimbriae
to attach themselves to the gut of an animal. When the animal sheds these
bacteria through defecation the life of the bacteria outside its host is
limited. However, they do have a survival mechanism. If the bacteria come
into contact with alternative host such as a living plant it can use its fimbriae to attach, derive nutrients and multiply.
Salmonella bacteria are very
common on raw egg shells, in poultry, and red meat; it is also a natural
part of the bacterial flora of reptiles and amphibians. In addition to
these common habitats for Salmonella, contaminated water is one of the
major sources for contraction of Salmonella illnesses worldwide. Similar to
E. coli, Salmonella has the ability to attach itself to plants as a
Anything that comes into
contact with fresh produce has the potential to contaminate it. A major
source of microbial contamination of fresh produce is indirect or direct
contact with feces. Potential sources of fecal contamination include
animals, untreated manure used as a soil amendment, water, infected
workers, or conditions in the field or packing facility, such as unclean
containers and tools used in harvesting and packing.