498 Chapter 28
methods and research. Many of these
organisms may be identifi ed as food - borne
pathogens in the future. Among these organ-
isms are the Gram - negative bacteria
Citrobacter , Edwardsiella , Enterobacter ,
Klebsiell a, Hafnia , Kluyvera , Proteus ,
Providencia , Morganella , Serrati a, Vibrios,
and Pseudomonas , and the Gram - positive
bacteria Corynebacterium , Streptococcus ,
and other species of Bacillus and Clostridium.
Miscellaneous organisms include Brucella ,
Mycobacterium (T, B), Coxiella burnetii
(Q - fever), Leptospirosis , Erysipela s, and
Tularemia.Food - Borne Viruses
Food - borne viruses are much less studied by
food microbiologists than are bacteria and
fungi, owing to the diffi culty of cultivating
these entities, as conventional bacteriologic
media will not allow these particles to grow.
There are, no doubt, many food - borne out-
breaks and cases caused by a variety of
viruses, but scientists in many cases are not
able to identify the sources of the infection.
Viruses that have been incriminated in food -
borne diseases include hepatitis A virus
(oysters, clams, doughnuts, sandwiches, and
salad), Norwalk virus (oysters), polio virus
(milk and oysters), ECHO virus (oysters),
enteroviruses (oysters), and coxsackievirus
(oysters). Much more research needs to be
done in the fi eld of food virology to help
reduce the incidents of food - borne diseases
caused by viruses. There were 56 total viral
outbreaks, 4,066 cases, and no deaths reported
in 2002.Protozoa and Related Organisms
Protozoans such as Cryptosporidium,
Cyclospora, Toxoplasma, Giardiasis,
Entamoeba, Balantidium, and others can also
cause human food - borne diseases. The most
sensational outbreak was the one involving
Cryptosporidium parvum, which affectedBecause the organism is a psychrotroph,
cold storage is not an adequate preventive
measure. Proper heating of food offers suf-
fi cient protection against this organism.
Consumption of undercooked food or raw
food such as raw shellfi sh is discouraged.
In 2002, no outbreak of this organism was
reported to the CDC.
Plesiomonas shigelloides
Plesiomonas shigelloides has been a suspect
in food - borne disease cases. The organism is
Gram - negative, facultative anaerobic, cata-
lase negative, and fermentative. It is oxidase
positive, which can be used to differentiate
it from other bacteria in the family
Enterobacteriaceae , since the latter is oxi-
dase - negative. The organism also resembles
Shigella but can be differentiated from
Shigella by being motile. It is capable of pro-
ducing many diseases, ranging from enteritis
to meningitis.
Gastroenteritis by P. shigellosides is
characterized by diarrhea, abdominal pain,
nausea, chills, fever, headache, and vomiting
after an incubation time of 1 to 2 days.
Symptoms last for a week or longer. All
reported foods involved with cases of gastro-
enteritis were from aquatic origin (salted fi sh,
crabs, and oysters). The organism can be iso-
lated from a variety of sources, including
humans, birds, fi sh, reptiles, and crustaceans.
The true nature of this organism as a food -
borne agent is not fully known because the
organism has not been well studied to date.
In 2002, no outbreak of this organism was
reported to the CDC.
Miscellaneous Bacterial Food - Borne
Pathogens
Many other microbes are suspected of being
food - borne pathogens. However, they are not
currently labeled as true food - borne patho-
gens, owing to a lack of reports on these
organisms, as well as a lack of isolation