580 Modern Food Microbiology
for 12 days failed to develop botulinal toxins.
70 Inoculated type E strains grew in controls, suggesting
that either the samples contained no botulinal spores or they were overgrown by other members of the
biota.
The development of mathematical models designed to predict the probability of growth and toxin
production in sous vide and MAP foods has been undertaken by several groups of investigators. By
the use of factorial designs, these models are designed to integrate the individual and combined effects
of the parameters of temperature, a w , pH, inoculum size, and storage time. Equations were developed
in one series of studies that could predict the length of time to toxin production and the probability
of toxigenesis by a single spore under defined conditions using cooked, vacuum-packed potatoes.
24
From the latter study, the response by mixtures of five each of types A and B spores was shown to be
linear, whereas to a w , the response was curvilinear. In another series of studies employing MAP-stored
fresh fish inoculated with nonproteolytic strains, 74.6% of experimental variation in the final multiple
linear regression model was accounted for by temperature of storage, with spore load accounting for
only 7.4%.
11 The earliest time to toxicity at 20
◦ C was 1 day, but at 4
◦ C the time increased to 18 days.
With type E spores, no growth was observed in chopped meat medium at 3
◦ C in 170 days, but in
vacuum-packaged herring inoculated with 10
4 type E spores per gram, toxigenesis was detected after
21 days at 3.3
◦ C.
11 Among other models reported is one that includes sorbic acid up to 2,270 ppm in
combination with some of the other parameters noted.
72
Nature of the Botulinal Neurotoxins
The neurotoxins are formed within the organism and released upon autolysis. They are produced
by cells growing under optimal conditions, although resting cells have been reported to form toxin
as well. The botulinal neurotoxins (BoNT) are the most toxic substances known, with purified type
A reported to contain about 30 million mouse LD 50 /mg. The minimum lethal dose for mice has been
reported also to be 0.4–2.5 ng/kg by intravenous or intraperitoneal injection, and a 50% human lethal
dose of about 1 ng/kg of body weight has been reported. The first of these toxins to be purified was
type A, which was achieved by Lamanna et al. and by Abrams et al., both in 1946. The purification of
B, E, and F has been achieved.
The genes for BoNT A, B, E, and F are chromosomal, whereas type G is plasmidborne.
128 The
type-G-producing strains cluster apart from the other botulinal strains consistent with their placement
in group IV. The gene for BoNT type B has been sequenced and cloned.
126
BoNT is produced as a single polypeptide chain that is posttranslationally nicked to form a di-chain
consisting of a 100-kDa heavy chain and a 50-kDa light chain held together by a disulfide bond. It
is composed of three domains: binding, translocation, and catalytic. The binding domain has been
used as an immunogen that affords protection against challenge doses of BoNT.
17 After BoNT binds
to nerve cell receptors, it is believed to be internalized into an endosome followed by proteolytic
cleavage of synaptobrevins (protein components of synaptic vesicles) that block neurotransmitter
release.
17
Type A toxin has been reported to be more lethal than B or E. Type B has been reported to
beassociated with a much lower case mortality than type A, and case recoveries from type B have
occurred even when appreciable amounts of toxin could be demonstrated in the blood.
Symptoms of botulism can be produced by either parenteral or oral administration of the toxins.
They may be absorbed into the blood stream through the respiratory mucous membranes, as well
as through the walls of the stomach and intestines. The toxins are not completely inactivated by
the proteolytic enzymes of the stomach, and, indeed, those produced by nonproteolytics may be
for 12 days failed to develop botulinal toxins.
70 Inoculated type E strains grew in controls, suggesting
that either the samples contained no botulinal spores or they were overgrown by other members of the
biota.
The development of mathematical models designed to predict the probability of growth and toxin
production in sous vide and MAP foods has been undertaken by several groups of investigators. By
the use of factorial designs, these models are designed to integrate the individual and combined effects
of the parameters of temperature, a w , pH, inoculum size, and storage time. Equations were developed
in one series of studies that could predict the length of time to toxin production and the probability
of toxigenesis by a single spore under defined conditions using cooked, vacuum-packed potatoes.
24
From the latter study, the response by mixtures of five each of types A and B spores was shown to be
linear, whereas to a w , the response was curvilinear. In another series of studies employing MAP-stored
fresh fish inoculated with nonproteolytic strains, 74.6% of experimental variation in the final multiple
linear regression model was accounted for by temperature of storage, with spore load accounting for
only 7.4%.
11 The earliest time to toxicity at 20
◦ C was 1 day, but at 4
◦ C the time increased to 18 days.
With type E spores, no growth was observed in chopped meat medium at 3
◦ C in 170 days, but in
vacuum-packaged herring inoculated with 10
4 type E spores per gram, toxigenesis was detected after
21 days at 3.3
◦ C.
11 Among other models reported is one that includes sorbic acid up to 2,270 ppm in
combination with some of the other parameters noted.
72
Nature of the Botulinal Neurotoxins
The neurotoxins are formed within the organism and released upon autolysis. They are produced
by cells growing under optimal conditions, although resting cells have been reported to form toxin
as well. The botulinal neurotoxins (BoNT) are the most toxic substances known, with purified type
A reported to contain about 30 million mouse LD 50 /mg. The minimum lethal dose for mice has been
reported also to be 0.4–2.5 ng/kg by intravenous or intraperitoneal injection, and a 50% human lethal
dose of about 1 ng/kg of body weight has been reported. The first of these toxins to be purified was
type A, which was achieved by Lamanna et al. and by Abrams et al., both in 1946. The purification of
B, E, and F has been achieved.
The genes for BoNT A, B, E, and F are chromosomal, whereas type G is plasmidborne.
128 The
type-G-producing strains cluster apart from the other botulinal strains consistent with their placement
in group IV. The gene for BoNT type B has been sequenced and cloned.
126
BoNT is produced as a single polypeptide chain that is posttranslationally nicked to form a di-chain
consisting of a 100-kDa heavy chain and a 50-kDa light chain held together by a disulfide bond. It
is composed of three domains: binding, translocation, and catalytic. The binding domain has been
used as an immunogen that affords protection against challenge doses of BoNT.
17 After BoNT binds
to nerve cell receptors, it is believed to be internalized into an endosome followed by proteolytic
cleavage of synaptobrevins (protein components of synaptic vesicles) that block neurotransmitter
release.
17
Type A toxin has been reported to be more lethal than B or E. Type B has been reported to
beassociated with a much lower case mortality than type A, and case recoveries from type B have
occurred even when appreciable amounts of toxin could be demonstrated in the blood.
Symptoms of botulism can be produced by either parenteral or oral administration of the toxins.
They may be absorbed into the blood stream through the respiratory mucous membranes, as well
as through the walls of the stomach and intestines. The toxins are not completely inactivated by
the proteolytic enzymes of the stomach, and, indeed, those produced by nonproteolytics may be