Foodborne Intoxications ◾ 329
Botulism by Clostridium botulinum 5,6
Importance
Foodborne botulism results following consumption of food containing the potent botulinum
toxin of Clostridium botulinum. It is a neurotoxin and produces neurological symptoms along
with some gastric symptoms. Unless prompt treatment is administered, it is quite fatal. Infant
botulism occurs from the ingestion by the infant of Clo. botulinum spores that germinate, grow,
and produce toxins in the GI tract and cause specific symptoms.
In the United States, the average number of outbreaks per year is about 15–16. From 1973 to
1983, there were a total of 231 outbreaks. This represents about 8% (231 out of 2841) of the total
reported foodborne outbreaks involving less than 4% (4984 out of 124,994) of the total cases.
However, out of a total of 247 deaths (2 per 1000 cases) from all foodborne diseases, 47 died of
botulism during this period (9.5 per 1000 cases) even with the medical treatment available in
this country. It is now estimated botulism causes about 55 cases with nine deaths annually in
the United States. 2 A majority of the outbreaks occur with foods prepared at home. Ethnic food
preparations have been implicated in many cases.
Characteristics
Organisms
Cells of Clo. botulinum strains are Gram-positive rods and occur as single cells or in small chains;
many are motile, obligate anaerobes and form single terminal spores. Cells are sensitive to low pH
(<4.6), low A W (0.93), and moderately high salt (5.5%). Spores do not germinate in the presence of
nitrite (250 ppm). Spores are highly heat resistant (killed at 115°C) but the cells are killed at moderate heat (pasteurization). Toxins are produced during growth. Strains can either be proteolytic
or nonproteolytic.
Growth
Clo. botulinum strains, on the basis of the type of toxin produced, have been divided into seven
types: A, B, C, D, E, F, and G. Of these, A, B, E, and F have been associated with human foodborne intoxications while involvement of serotype G in human infection is not established yet.
Type A strains are proteolytic, type E strains are nonproteolytic, but types B and F strains can be
either proteolytic or nonproteolytic. The proteolytic strains can grow between 10°C and 48°C with
the optimum at 35°C. The nonproteolytic strains grow optimally at 30°C with a range between
3.3°C and 45°C. Optimum growth facilitates optimum toxin production. An anaerobic condition
is necessary for growth. Spore germination and outgrowth prior to cell multiplication is favored
in the environment of cell growth. Similarly, conditions that prevent cell growth also adversely
affect spore germination. As indicated before, either pH 4.6, A w 0.93, or 5.5% NaCl can prevent
cell growth; but by using two or more parameters along with lower temperatures, the lower growth
limits of any of the above parameters can be greatly reduced. 4
Habitat
Spores of Clo. botulinum are widely distributed in soil, sewage, mud, sediments of marshes, lakes
and coastal waters, plants, and the intestinal contents of animals and fish. Fruits and vegetables
Botulism by Clostridium botulinum 5,6
Importance
Foodborne botulism results following consumption of food containing the potent botulinum
toxin of Clostridium botulinum. It is a neurotoxin and produces neurological symptoms along
with some gastric symptoms. Unless prompt treatment is administered, it is quite fatal. Infant
botulism occurs from the ingestion by the infant of Clo. botulinum spores that germinate, grow,
and produce toxins in the GI tract and cause specific symptoms.
In the United States, the average number of outbreaks per year is about 15–16. From 1973 to
1983, there were a total of 231 outbreaks. This represents about 8% (231 out of 2841) of the total
reported foodborne outbreaks involving less than 4% (4984 out of 124,994) of the total cases.
However, out of a total of 247 deaths (2 per 1000 cases) from all foodborne diseases, 47 died of
botulism during this period (9.5 per 1000 cases) even with the medical treatment available in
this country. It is now estimated botulism causes about 55 cases with nine deaths annually in
the United States. 2 A majority of the outbreaks occur with foods prepared at home. Ethnic food
preparations have been implicated in many cases.
Characteristics
Organisms
Cells of Clo. botulinum strains are Gram-positive rods and occur as single cells or in small chains;
many are motile, obligate anaerobes and form single terminal spores. Cells are sensitive to low pH
(<4.6), low A W (0.93), and moderately high salt (5.5%). Spores do not germinate in the presence of
nitrite (250 ppm). Spores are highly heat resistant (killed at 115°C) but the cells are killed at moderate heat (pasteurization). Toxins are produced during growth. Strains can either be proteolytic
or nonproteolytic.
Growth
Clo. botulinum strains, on the basis of the type of toxin produced, have been divided into seven
types: A, B, C, D, E, F, and G. Of these, A, B, E, and F have been associated with human foodborne intoxications while involvement of serotype G in human infection is not established yet.
Type A strains are proteolytic, type E strains are nonproteolytic, but types B and F strains can be
either proteolytic or nonproteolytic. The proteolytic strains can grow between 10°C and 48°C with
the optimum at 35°C. The nonproteolytic strains grow optimally at 30°C with a range between
3.3°C and 45°C. Optimum growth facilitates optimum toxin production. An anaerobic condition
is necessary for growth. Spore germination and outgrowth prior to cell multiplication is favored
in the environment of cell growth. Similarly, conditions that prevent cell growth also adversely
affect spore germination. As indicated before, either pH 4.6, A w 0.93, or 5.5% NaCl can prevent
cell growth; but by using two or more parameters along with lower temperatures, the lower growth
limits of any of the above parameters can be greatly reduced. 4
Habitat
Spores of Clo. botulinum are widely distributed in soil, sewage, mud, sediments of marshes, lakes
and coastal waters, plants, and the intestinal contents of animals and fish. Fruits and vegetables