708 Part VII: Food Safety
Ontario, Canada, in 2000 was related to government
cutbacks in the number of inspections and uncer-
tainty over reporting procedures (MacKay 2002).
Finally, microbial adaptation is an important rea-
son for the emergence of new pathogens (Altekruse
et al. 1997). Natural selection and the overuse of
antibiotics, both in humans and in animal feed, have
led to the emergence of a number of new hardy
strains of pathogenic bacteria. Chemical treatments
have also had an effect. For instance, the virulence
plasmid of Yersinia enterocoliticahas been associat-
ed with resistance to arsenate and arsenite (Neyt et
al. 1997). The spread of this pathogen has been
linked to the previous practice on pig farms of
spreading arsenic to prevent spirochetal infections
(Tauxe 2002).
COMMON FOODBORNE
PATHOGENS
Food recalls are expensive for the food industry. In
order to avoid unnecessary recalls, the food industry
is only interested in detecting bacteria that may po-
tentially cause illness. Many bacterial pathogens are
closely related to nonpathogenic bacteria that may
inhabit the same environments. These related bacte-
ria may be members of the same genus or even dif-
ferent strains of the same species. A good detection
method for the pathogen must be able to distinguish
between the pathogens and closely related non-
pathogens. Toxins produced by pathogenic bacteria
often provide a convenient way to detect the organ-
isms. In general, only the pathogenic strains will
produce protein toxins, making these proteins, or the
genes encoding them, ideal targets for rapid differ-
entiation between potential pathogens and non-
pathogens. The following summarizes some of the
common pathogens and their toxins (see Table
31.2). Methodologies for detecting the pathogens or
their toxins are provided later in the chapter.
CAMPYLOBACTER JEJUNI
There are 12 species of the Gram-negative Campy-
lobactergenus known to be of clinical importance.
Of these, C. jejuniand C. coliaccount for 95% of
Campylobacterinfections in humans (Park 2002).
C. jejuniwas recognized as a foodborne pathogen in
the 1970s and is now known to be one of the leading
causes of foodborne illness in the industrialized
world (Gugnani 1999). The main infective route is
through consumption of raw or undercooked poultry
products, including eggs (Park 2002). It is thought
that C. jejunican spread through a population of
chickens via the water system (Tauxe 2002).
Infection with C. jejunicauses diarrhea, abdomi-
nal pain, and fever (Gugnani 1999). Campylobacter
species have also been identified as one of the most
common infections preceding Guillain-Barré syn-
drome, a peripheral nervous system condition in-
volving acute flaccid paralysis (Meng and Doyle
2002). Campylobacterinfections are responsible for
about 5% of annual food-related deaths in the
United States (Mead et al. 1999).
Campylobacterspecies are unusual in that they
exhibit fastidious growth requirements and display
an unusual sensitivity to environmental stress. For
instance, members of the genus are microaerophilic
and have an optimal growth temperature of 42°C,
but are unable to grow at temperatures below 30°C.
Desiccation and osmotic stress will kill the bacteria.
They cannot grow at salt concentrations above 2%,
are killed at pH values less than 4.9, and cannot sur-
vive heating and pasteurization processes (Park
2002). UnlikeCampylobacter, most foodborne path-
ogens are extremely robust, thereby surviving most
treatments used to eradicate pathogens from food.
Campylobacteris not hardy, and yet it has emerged
as the single leading cause of foodborne illness in
the Western world (Kopecko et al. 2001, Park 2002).
C. jejuniproduces at least one cytotoxin, cyto-
lethal distending toxin (CDT). While little is known
about the effects of this toxin, cell culture studies
indicate that it causes cell division to stop at the G2
phase (Whitehouse et al. 1998). There is some spec-
ulation that this may potentially cause loss of func-
tion or erosion of the epithelial layer of the intestine,
where the bacteria tend to colonize, leading to diar-
rhea (Park 2002). Given that the toxin is universal to
C. jejuni, it makes a good detection target.SALMONELLASPP.Nontyphoidal salmonellosis is one of the major bac-
terial illnesses caused by food in industrialized
countries. There are five species within the Salmo-
nellagenus, of which S. enterica, subspecies enteri-
ca, is the most relevant to illness in warm-blooded
animals. Of the over 1500 serotypes within the sub-
species, the two serotypes S. typhimuriumand S.