Fundamental Food Microbiology, Third Edition - Fuad Fathir

350 FUNDAMENTAL FOOD MICROBIOLOGY
Proteolytic strains can grow between 10�C and ca. 48�C, with the optimum at 35�C.
Nonproteolytic strains grow optimally at 30�C, with a range from 3.3 to 45�C. Optimum
growth facilitates optimum toxin production. Anaerobic conditions are necessary
for growth. Spore germination and outgrowth before cell multiplication are favored in
the environment of cell growth. Similarly, conditions that prevent cell growth also
adversely affect spore germination. A pH of 4.6, A w of 0.93, or 5.5% NaCl can prevent
cell growth, but by using two or more parameters along with lower temperature, the
lower growth limits of any of the given parameters can be greatly reduced. 9–11
3. Habitat
Spores of Clo. botulinum are widely distributed in soil, sewage, mud, sediments of
marshes, lakes and coastal waters, plants, and intestinal contents of animals and
fishes. Fruits and vegetables can be contaminated with spores from soil, fishes from
water and sediments, and various other foods from many of the given sources. Type
A and B spores are more prevalent in soil, sewage, and fecal matters of animals,
whereas Type E spores are generally found in marine environments. Type A spores
are predominant in western U.S. and Type B spores are found predominantly in
eastern U.S. and different parts of the world. 9–11
C. Toxins and Toxin Production
The toxins of Clo. botulinum are neurotoxic proteins. In general, toxins associated
with food intoxication in humans (Types A, B, E, and F) are extremely potent, and
only a small amount of toxin is required to produce the symptoms and cause death.
Following ingestion, toxin molecules are absorbed from the upper portion of the
intestine through the intestinal wall and spread via the blood to the peripheral nerves.
The toxins block signal transfers, irreversibly causing paralysis of all involuntary
muscles. The toxins move slowly through the body. Toxins produced by nonproteolytic
strains are not fully activated; trypsin treatment is necessary to activate them
(this occurs in the digestive tract). The toxins are heat labile and can be destroyed
in a contaminated food by high and uniform heat, such as 90�C for 15 min or boiling
for 5 min. Radiation at 5 to 7 mrad can also destroy them. 10,11
Cell growth is necessary for toxin production. At optimum growth temperature,
toxins are produced in large amounts. However, at both extreme growth ranges,
enough toxin can be produced by a strain in a food to cause disease and death
following ingestion.
D. Disease and Symptoms
Botulism is caused by ingestion of the neurotoxin botulin formed in a food. The
toxins are absorbed from the intestine, spread to the peripheral nerves, and block
the transmission of impulse. However, at the initial stage (generally 12 to 36 h, but
can be 2 h), some gastrointestinal disorders (e.g., nausea, vomiting, diarrhea, and
constipation) may be evident. Neurological symptoms develop within a short time,
especially if the amount of botulin consumed is high. As they are highly potent