31 Emerging Bacterial Foodborne Pathogens and Methods of Detection 707incidence in the next two decades (Gugnani 1999).
Fourth, the pathogen may already be a recognized
problem in some parts of the world, but is increasing
significantly in its geographic range (Schlundt
2001). These definitions are illustrated using a few
pathogens that have been classified as “emerging.”
For example, Escherichia coliO157:H7 evolved rel-
atively recently and may be a new pathogen. Vibrio
vulnificushas existed for centuries but has only re-
cently been recognized as causing illness. Finally,
Listeria monocytogenesand Vibrio choleraeare
well-known bacterial pathogens, but their transmis-
sion in foods has only recently been recognized
(Mead et al. 1999).
In 2002, Tauxe (2002) examined the shifting
spectrum of foodborne pathogens over time. Many
of the significant bacterial pathogens at the turn of
the previous century are now extremely uncommon
in the clinical setting. These include Salmonella
typhi, Brucella, and Clostridium botulinum. Further-
more, of the 27 main microbial pathogens known to
cause foodborne illnesses, 13 (including bacteria,
viruses, and protozoa) have emerged in the last 25
years. These 13 account for 82% of the foodborne
illness (or 13.8 million illnesses in the United
States), and 61% of the 1800 deaths caused by
known pathogens (Mead et al. 1999, Tauxe 2002).
We have an appalling lack of knowledge about
foodborne pathogens. For example, if all of the 27
known foodborne pathogens are taken into account,
only 19% of the estimated number of foodborne ill-
nesses and 36% of the deaths are accounted for,
meaning that there must be a number of foodborne
pathogens that have not been identified (Tauxe 2002).
Of those illnesses caused by known pathogens, three
pathogens,Salmonella, Listeria, andToxoplasma
(a parasite), cause more than 75% of the deaths
(Mead et al. 1999).
In this chapter a few of the more common emerg-
ing bacterial foodborne pathogens will be described
and some of the reasons for the pathogens to emerge
and the reasons why these bacteria are of concern
will be examined. The chapter will cover the toxins
that these bacteria produce, how the toxins mediate
some of the pathogenic properties of the bacteria,
and how these toxins can be used to detect the path-
ogens. The final section of the chapter will focus on
methodologies used to detect pathogens in an at-
tempt to keep them out of the food chain.
FACTORSAFFECTING THEEMERGENCE OF
NEWPATHOGENSA number of factors contribute to the emergence of
foodborne pathogens. One of the most important is
the changing demographics of the Western world.
The median age of the population has been increas-
ing steadily over the past few decades. As well, with
the advent of HIV, and advances in treatments for
chronic diseases, there are an increasing number of
people who are immunodeficient. These factors have
led to an increase in the proportion of the population
that is susceptible to a number of foodborne diseases
(Altekruse et al. 1997). Another factor that con-
tributes to the emergence of pathogens is changes in
human behavior. Fresh fruit and vegetable consump-
tion increased by 50% between 1970 and 1994 in
the United States. In addition to this, people eat out-
side of the home much more regularly than at any
other time in history, and these foods cause about
80% of the outbreaks seen in the United States
(Altekruse et al. 1997).
Changing practices in industry and differences in
technology can affect pathogen distribution. With
the consolidation of many processing facilities, con-
tamination is likely to affect more people. Increased
consolidation also means longer transport distances,
providing more time for growth of pathogenic or-
ganisms. Related to this increase in transportation
are the changes in travel and commerce. With global
trade, more people are travelling, exposing more
people to different foods, with a higher probability
of acquiring infections. Increasing global trade also
means more international transport of foods. These
foods may not be exposed to the same inspection
standards. Increased immigration and the foods made
popular by immigrants have also contributed to ex-
posure to different pathogens (Altekruse et al. 1997).
Other factors that contribute to the emergence of
new pathogens are changing land use and a break-
down of the public health infrastructure in North
America (Altekruse et al. 1997). Changing land use
involves problems such as the disposal of waste
from feedlots and other commercial animal-raising
facilities. The breakdown of the public health infra-
structure relates to the decreasing budgets of many
of the agencies responsible for looking into food and
water safety. For instance, one of the contributing
factors to theE. coliO157:H7 outbreak in Walkerton,