Microbial Hazards in Foods: Food-Borne Infections and Intoxications 485be found on human skin, nose, hair, and
many food items. The organisms, when
allowed to grow in food, may produce a class
of low molecular weight (ca 30,000 daltons)
protein toxins called staphylococcal entero-
toxins (A, B, C 1 , C 2 , C 3 , D, E, and maybe
others). These toxins, when ingested by a
susceptible person, will cause severe nausea,
vomiting, abdominal cramps, diarrhea, and
prostration about 4 to 6 hours after consump-
tion. Recovery is about 24 to 72 hours.
Victims usually will not die, but they may
wish they had, as the reactions are very
violent. Also, there is no immunity against
the toxins; thus a person can have staphylo-
coccal intoxication repeatedly. Along with
Salmonella and Clostridium perfringens ,
staphylococcal intoxication has ranked
among the top - three agents of food - borne
disease in the past 40 years. In 2002, there
were 42 outbreaks, involving 1,413 cases and
1 death. Since this is a nonreportable disease,
many more outbreaks and cases occur regu-
larly without being known to public health
offi cials.
These toxins are heat stable. Once formed
in food, the toxin is very hard to destroy.
Heating the toxins at 80 ° C for 5 hours will
not destroy the toxin. Boiling for 3 hours will
destroy the toxin, and cooking under pressure
(121 ° C) will inactivate the toxin in 30
minutes. For practical purposes, these toxins
are not inactivated by normal cooking
procedures.
Due to the fact that the enterotoxins are
heat stable, detection of live Staphylococcus
aureus in foods has only limited value in
terms of assessing the potential of the food
to cause staphylococcal food intoxication.
For example, if a food is contaminated with
a toxigenic strain of S. aureus and the organ-
isms grow to 1 million cells, they will then
release large amounts of enterotoxins (in
micrograms) into the food. When the food is
subsequently cooked, even though live S.
aureus cannot be found in it, the food is still
capable of causing a case of staphylococcalproduced by a biologic system. It has been
estimated that one pure ounce of toxin can
kill 200 million people. Treat ment is by the
administration of monovalent E, bivalent
AB, trivalent ABE, or polyvalent ABCDEF
antisera.
The toxins can be detected by animal tests
using mice, as well as immunologic tests
using specifi c antibodies (gel diffusion tests,
ELISA, RIA tests, etc). Recently, a rapid
Polymerase Chain Reaction (PCR) method
has been employed to detect the botulin gene
harbored by cultures isolated from foods.
The information, however, does not directly
imply that the food is toxigenic and harbors
the toxin.
Fortunately, the toxins are heat sensitive.
Boiling of the toxin for 10 minutes will
destroy it. The key to preventing botulism is
to know the composition (pH, A w oxidation -
reduction potential, presence of inhibitory
compounds, etc.) of the food and to utilize
proper time and temperature for processing
as well as correct packaging and storage of
the processed food. All high - moisture, low -
acid foods processed and then stored under
anaerobic conditions, whether in cans, glass
bottles, or pouches, should be subject to close
scrutiny to avoid the possibility of C. botuli-
num surviving and later germinating and pro-
ducing the toxins. Since there are proteolytic
and nonproteolytic strains of C. botulinum,
the absence of off - odor from a suspected
canned food cannot guarantee the safety of
the food. Never taste a suspected food or use
food from swollen, dented, or deformed cans.
When in doubt, always boil the suspected
food for 10 minutes before discarding it. The
use of nitrites in fermented meat such as sau-
sages is to prevent the germination of the
Clostridium botulinum spores.
Staphylococcus aureus
Staphylococcus aureus is a Gram - positive,
facultative anaerobic coccus occurring in
clusters. The organism is ubiquitous and can