576 Modern Food Microbiology
The first type F strains were isolated by Moller and Scheibel
86 from a homemade liver paste
incriminated in an outbreak of botulism, involving one death, on the Danish island Langeland. Since
that time, Craig and Pilcher
20 have isolated type F spores from salmon caught in the Columbia River;
Eklund and Poysky
29 found type F spores in marine sediments taken off the coasts of Oregon and
California; Williams-Walls
127 isolated two proteolytic strains from crabs collected from the York River
in Virginia; and Midura et al.
82 isolated the organism from venison jerky in California.
The type G strain was isolated first in 1969 from soil samples in Argentina,
37 and it was isolated
later from five human corpses in Switzerland.
109 These deaths were not food associated. It has not
been incriminated in food-poisoning outbreaks to date, and the reason might be due to the fact that this
strain produces considerably less neurotoxin than type A. It has been shown that type G produced 40
LD 50 /ml of toxin in media in which type A normally produces 10,000 to 1,000,000 LD 50 /ml, but that
under certain conditions the organism could be induced to produce up to 90,000 LD 50 /ml of medium.
19
For a review of the prevalence of C. botulinum spores in other environmental samples, see reference 10.
Growth of C. botulinum Strains
Some of the growth and other characteristics of the strains that cause botulism in humans are summarized in Table 24–3. The discussion that follows emphasizes the differences between the proteolytic
and nonproteolytic strains irrespective of serological type. The proteolytic strains, unlike the nonproteolytics, digest casein and produce H 2 S. The latter, on the other hand, ferment mannose, whereas
the proteolytics do not. The proteolytics and nonproteolytics have been shown to form single groups
relative to somatic antigens as evaluated by agglutination.
108 The absorption of antiserum by any one
of a group removes antibodies from all three of that group.
The nutritional requirements of these organisms are complex, with amino acids, B vitamins, and
minerals being required. Synthetic media have been devised that support growth and toxin production
of most types. The proteolytic strains tend not to be favored in their growth by carbohydrates, whereas
the nonproteolytics are. At the same time, the nonproteolytics tend to be more fermentative than the
proteolytic types.
The proteolytics generally do not grow below 12.5
◦ C, although a few reports exist in which growth
was detected at 10
◦ C. The upper range for types A and proteolytic B, and presumably for the other
proteolytic types, is about 50
◦ C. On the other hand, the nonproteolytic strains can grow as low as
3.3
◦ C with the maximum about 5
◦ below that for proteolytics. Minimum and maximum temperatures
of growth of these organisms are dependent on the state of other growth parameters, and the minima
and maxima noted may be presumed to be at totally optimal conditions relative to pH, a w , and the
like. In a study of the minimum temperature for growth and toxin production by nonproteolytic types
B and F in broth and crabmeat, both grew and produced toxin at 4
◦ C in broth, but in crabmeat, growth
and toxin production occurred only at 26
◦ C and not at 12
◦ C or lower.
107 A type G strain grew and
produced toxin in broth and crabmeat at 12
◦ C but not at 8
◦ C.
107
The minimum pH that permits growth and toxin production of C. botulinum strains has been the
subject of many studies. It is generally recognized that growth does not occur at or below pH 4.5, and it
is this fact that determines the degree of heat treatment given to foods with pH values below this level
(see Chapter 17). Because of the existence of botulinal toxins in some high-acid, home-canned foods,
this area has been the subject of recent studies. In one study, no growth of types A and B occurred in
tomato juice at a pH around 4.8, but when the product was inoculated with Aspergillus gracilis, toxin
The first type F strains were isolated by Moller and Scheibel
86 from a homemade liver paste
incriminated in an outbreak of botulism, involving one death, on the Danish island Langeland. Since
that time, Craig and Pilcher
20 have isolated type F spores from salmon caught in the Columbia River;
Eklund and Poysky
29 found type F spores in marine sediments taken off the coasts of Oregon and
California; Williams-Walls
127 isolated two proteolytic strains from crabs collected from the York River
in Virginia; and Midura et al.
82 isolated the organism from venison jerky in California.
The type G strain was isolated first in 1969 from soil samples in Argentina,
37 and it was isolated
later from five human corpses in Switzerland.
109 These deaths were not food associated. It has not
been incriminated in food-poisoning outbreaks to date, and the reason might be due to the fact that this
strain produces considerably less neurotoxin than type A. It has been shown that type G produced 40
LD 50 /ml of toxin in media in which type A normally produces 10,000 to 1,000,000 LD 50 /ml, but that
under certain conditions the organism could be induced to produce up to 90,000 LD 50 /ml of medium.
19
For a review of the prevalence of C. botulinum spores in other environmental samples, see reference 10.
Growth of C. botulinum Strains
Some of the growth and other characteristics of the strains that cause botulism in humans are summarized in Table 24–3. The discussion that follows emphasizes the differences between the proteolytic
and nonproteolytic strains irrespective of serological type. The proteolytic strains, unlike the nonproteolytics, digest casein and produce H 2 S. The latter, on the other hand, ferment mannose, whereas
the proteolytics do not. The proteolytics and nonproteolytics have been shown to form single groups
relative to somatic antigens as evaluated by agglutination.
108 The absorption of antiserum by any one
of a group removes antibodies from all three of that group.
The nutritional requirements of these organisms are complex, with amino acids, B vitamins, and
minerals being required. Synthetic media have been devised that support growth and toxin production
of most types. The proteolytic strains tend not to be favored in their growth by carbohydrates, whereas
the nonproteolytics are. At the same time, the nonproteolytics tend to be more fermentative than the
proteolytic types.
The proteolytics generally do not grow below 12.5
◦ C, although a few reports exist in which growth
was detected at 10
◦ C. The upper range for types A and proteolytic B, and presumably for the other
proteolytic types, is about 50
◦ C. On the other hand, the nonproteolytic strains can grow as low as
3.3
◦ C with the maximum about 5
◦ below that for proteolytics. Minimum and maximum temperatures
of growth of these organisms are dependent on the state of other growth parameters, and the minima
and maxima noted may be presumed to be at totally optimal conditions relative to pH, a w , and the
like. In a study of the minimum temperature for growth and toxin production by nonproteolytic types
B and F in broth and crabmeat, both grew and produced toxin at 4
◦ C in broth, but in crabmeat, growth
and toxin production occurred only at 26
◦ C and not at 12
◦ C or lower.
107 A type G strain grew and
produced toxin in broth and crabmeat at 12
◦ C but not at 8
◦ C.
107
The minimum pH that permits growth and toxin production of C. botulinum strains has been the
subject of many studies. It is generally recognized that growth does not occur at or below pH 4.5, and it
is this fact that determines the degree of heat treatment given to foods with pH values below this level
(see Chapter 17). Because of the existence of botulinal toxins in some high-acid, home-canned foods,
this area has been the subject of recent studies. In one study, no growth of types A and B occurred in
tomato juice at a pH around 4.8, but when the product was inoculated with Aspergillus gracilis, toxin