Handbook of Meat Processing

Microbial Hazards in Foods: Food-Borne Infections and Intoxications 487

Unlike exotoxins, antibodies will not neutral-

ize toxicity because the toxic part is the lipid.

All endotoxins have the same action and are

released when the Gram - negative bacterium

undergoes lysis. These endotoxins cause

fever by acting as exogenous pyrogens. The

exogenous pyrogen, when absorbed into the

bloodstream, causes injury to the leukocytes,

which in turn release an endogenous pyrogen.

This endogenous pyrogen stimulates the ther-

moregulatory center of the brain at the hypo-

thalamus and causes fever. Therefore, fever

in a patient is indicative of a food - borne

infection case.

Endotoxins can be detected by the limulus

amebocyte lysate (LAL) test. In the presence

of endotoxins, the LAL will form a gel. The

reaction takes about 1 hour. Hospital materi-

als should be pyrogen - free, and LAL is the

standard test for pyrogens in hospital sup-

plies and environment. Because endotoxins

are released upon lysis of the cell, it is advis-

able in certain cases that antibiotics not be

administered in mild food infection cases.

Lysis of cells by antibiotics intended for

other infections such as Escherichia coli

O157 : H7 may allow the release of other

harmful toxins in the intestinal tract, causing

a more severe infection case.

Bacterial Infection

Clostridium perfringens

Clostridium perfringens occupies an interest-

ing position, since it is both a food - borne

infection agent as well as a food - borne intox-

ication agent. On the one hand, the suscep-

tible person has to ingest large numbers of

viable C. perfringens before coming down

with a food - poisoning case, and on the other

hand, the organism produces an enterotoxin

to cause the illness. In 2002 in the United

States, there were 57 outbreaks and 2,772

cases, with no deaths reported. It is estimated,

however, that 250,000 cases occur annually,

with an average of 7.6 deaths per year at an

sumed food heavily contaminated with
molds. The toxins can be detected by animal
tests using ducklings or chick embryo. Thin -
layer chromatography and high - performance
liquid chromatography can also be used to
detect these toxins. Recently, monoclonal
antibodies have been employed to detect
these toxins with great rapidity (10 to 30 min)
and sensitivity (1 ppb and lower). Attempts
to detoxify afl atoxin by ozone, peroxides,
and ammonia have met with limited success.
Thus, the best preventive measure is not to
allow the mold to contaminate the food
and feed, and keep these commodities in
a dry environment unfavorable for mold
growth.

Exotoxins versus Endotoxins

It is necessary to differentiate these toxins
before having a discussion on food - borne
infections.
Exotoxins are toxins produced by an
organism and later released into the environ-
ment. The cell remains alive and intact.
Ingestion of these preformed toxins causes
food - borne intoxication. These toxins are
protein toxins, mainly produced by Gram -
positive organisms. Because they are pro-
teins, they can be neutralized by corresponding
antibodies and detected by a variety of immu-
nologic methods. These toxins are relatively
heat sensitive (except the staphylococcal
enterotoxins described earlier). These
toxins also have a distinct pharmacology.
Examples of exotoxins are staphylococcal
enterotoxins (affecting the intestinal tracts)
and botulinum neurotoxins (affecting the
nervous system).
Endotoxins are part of the cell wall mate-
rial of Gram - negative cells. Every Gram -
negative bacterium examined has endotoxins.
These are complex molecules containing
protein, carbohydrate, and lipid. The protein
moiety determines antigenicity, the carbohy-
drate moiety determines immunologic speci-
fi city, and the lipid moiety causes toxicity.