Bacterial Pathogens, Mycotoxins, Viruses, Parasites, and Fish Toxins ◾ 389
muddy beds. Also, because of fecal contamination, they can be present in raw foods of animal,
bird, and plant origin. In heat-treated foods, their presence indicates either improper heating or
post-heat contamination, or both. They can grow rapidly in most foods under optimum growth
conditions. They are not expected to grow in foods held in refrigeration (3°C–4°C or below)
even for a long time. Foods with low pH (4.5), low A W (0.95), and salt (5%) discourage their
growth.
Disease-Causing Potential
Ple. shigelloides strains were implicated in many human gastroenteritis outbreaks associated with
contaminated drinking water. In many cases, the organisms were isolated from both the implicated water and stools of affected people. The typical symptoms are diarrhea, nausea, and abdominal pain; many can also have vomiting, fever, and chills. The incubation period ranged from 24 to
50 hours, and the symptoms lasted for one to nine days. Several incidents of gastroenteritis from
the consumption of seafood, oysters, crabs, and fish were suspected to be the result of Ple. shigelloides. In some instances, the organisms were isolated both from foods and stools of patients. In
these cases, foods were eaten either raw or after being improperly cooked or stored.
It is difficult to confirm a direct involvement of Ple. shigelloides in human foodborne gastroenteritis. Ple. shigelloides was isolated in stools from both unaffected people and individuals suffering from gastroenteritis. Thus, these strains are considered as opportunistic pathogens, affecting
individuals with less resistance, such as the young, old, and sick. In addition to gastroenteritis,
several strains are associated with bacteremia and septicemia. Several studies demonstrated that
Ple. shigelloides strains produce cholera-like enterotoxins and heat-stable and heat labile enterotoxins that may be responsible for diarrhea.
Non-escherichia coli coliforms
Coliform groups include species from genera Escherichia, Klebsiella, Enterobacter, and Citrobacter,
all belonging to the family Enterobacteriaceae (see Table 30.1) and thus sharing some common
characteristics. Previously, Escherichia coli strains (both nonpathogenic and pathogenic) were
thought to mainly inhabit the intestinal tract of humans and warm-blooded animals and birds,
and most species in the other three genera were thought to be mainly of nonintestinal origin.
However, other studies have shown that species and strains from Klebsiella, Enterobacter, and
Citrobacter (together referred to as non-Esc. coli coliforms) can colonize the human gut and produce potent enterotoxins. In several acute and chronic cases of diarrhea, they were isolated from
stools and the intestinal tract. Some isolates of Enterobacter cloacae, Klebsiella pneumonia, and
Citrobacter spp. were found to produce enterotoxins similar to heat-labile or heat-stable toxins of
enterotoxigenic Esc. coli. In enterotoxigenic Esc. coli, these traits are plasmid linked. The ability
of non-Esc. coli coliforms to produce enterotoxins similar to those of pathogenic Esc. coli strains
probably results from the intergeneric (horizontal gene transfer) transfer of plasmids encoding
these phenotypes.
Non-Esc. coli coliforms are normally present in raw food materials as well as in some pasteurized foods because of post-heat contamination. They can grow in many foods if the growth parameters are not limiting. Some strains can grow at refrigerated temperatures. Temperature abuse
during storage can also facilitate their rapid growth in a food. The significance of their presence
in a food may need to be reevaluated. The ability of food isolates to produce enterotoxins may be
included in test protocols.
muddy beds. Also, because of fecal contamination, they can be present in raw foods of animal,
bird, and plant origin. In heat-treated foods, their presence indicates either improper heating or
post-heat contamination, or both. They can grow rapidly in most foods under optimum growth
conditions. They are not expected to grow in foods held in refrigeration (3°C–4°C or below)
even for a long time. Foods with low pH (4.5), low A W (0.95), and salt (5%) discourage their
growth.
Disease-Causing Potential
Ple. shigelloides strains were implicated in many human gastroenteritis outbreaks associated with
contaminated drinking water. In many cases, the organisms were isolated from both the implicated water and stools of affected people. The typical symptoms are diarrhea, nausea, and abdominal pain; many can also have vomiting, fever, and chills. The incubation period ranged from 24 to
50 hours, and the symptoms lasted for one to nine days. Several incidents of gastroenteritis from
the consumption of seafood, oysters, crabs, and fish were suspected to be the result of Ple. shigelloides. In some instances, the organisms were isolated both from foods and stools of patients. In
these cases, foods were eaten either raw or after being improperly cooked or stored.
It is difficult to confirm a direct involvement of Ple. shigelloides in human foodborne gastroenteritis. Ple. shigelloides was isolated in stools from both unaffected people and individuals suffering from gastroenteritis. Thus, these strains are considered as opportunistic pathogens, affecting
individuals with less resistance, such as the young, old, and sick. In addition to gastroenteritis,
several strains are associated with bacteremia and septicemia. Several studies demonstrated that
Ple. shigelloides strains produce cholera-like enterotoxins and heat-stable and heat labile enterotoxins that may be responsible for diarrhea.
Non-escherichia coli coliforms
Coliform groups include species from genera Escherichia, Klebsiella, Enterobacter, and Citrobacter,
all belonging to the family Enterobacteriaceae (see Table 30.1) and thus sharing some common
characteristics. Previously, Escherichia coli strains (both nonpathogenic and pathogenic) were
thought to mainly inhabit the intestinal tract of humans and warm-blooded animals and birds,
and most species in the other three genera were thought to be mainly of nonintestinal origin.
However, other studies have shown that species and strains from Klebsiella, Enterobacter, and
Citrobacter (together referred to as non-Esc. coli coliforms) can colonize the human gut and produce potent enterotoxins. In several acute and chronic cases of diarrhea, they were isolated from
stools and the intestinal tract. Some isolates of Enterobacter cloacae, Klebsiella pneumonia, and
Citrobacter spp. were found to produce enterotoxins similar to heat-labile or heat-stable toxins of
enterotoxigenic Esc. coli. In enterotoxigenic Esc. coli, these traits are plasmid linked. The ability
of non-Esc. coli coliforms to produce enterotoxins similar to those of pathogenic Esc. coli strains
probably results from the intergeneric (horizontal gene transfer) transfer of plasmids encoding
these phenotypes.
Non-Esc. coli coliforms are normally present in raw food materials as well as in some pasteurized foods because of post-heat contamination. They can grow in many foods if the growth parameters are not limiting. Some strains can grow at refrigerated temperatures. Temperature abuse
during storage can also facilitate their rapid growth in a food. The significance of their presence
in a food may need to be reevaluated. The ability of food isolates to produce enterotoxins may be
included in test protocols.