Food Poisoning Caused by Gram-Positive Sporeforming Bacteria
569
observed.
92 At least 13 amino acids are required for growth, along with biotin, pantothenate, pyridoxal,
adenine, and other related compounds. It is heterofermentative, and a large number of carbohydrates
are attacked. Growth is inhibited by around 5% NaCl.
The endospores of food-poisoning strains differ in their resistance to heat, with some being typical of other mesophilic spore formers and some being highly resistant. A D 100 ◦ C value of 0.31 for
C. perfringens (ATCC 3624) and a value of 17.6 for strain NCTC 8238 have been reported.
123 For
eight strains that produced reactions in rabbits, D 100 ◦ C values ranged from 0.70 to 38.37; strains that
did not produce rabbit reactions were more heat sensitive.
115 Differences in heat sensitivity among
C. perfringens strains is associated with the carriage of the cpe gene. D 100 ◦ C values for 13 meat,
poultry, and fish isolates where the cpe gene is chromosomal ranged from a low of 43 to a high of 170,
while a non-outbreak strain that carried cpe on plasmids was 3.
124 These authors noted that outbreak
strains typically possess a D 100 ◦ C >40 while non-outbreak strains are typically <2.
In view of the practice of cooking roasts in water baths for long times at low temperatures (LTLT),
the heat destruction of vegetative cells of C. perfringens has been studied by several groups. For
strain ATCC 13124 in autoclaved ground beef, D 56.8 ◦ C was 48.3 minutes, essentially similar to the
D 56.8 ◦ C or D 47.9 ◦ C for phospholipase C.
32 Employing strain NCTC 8798, D values for cells were
found to increase with increasing growth temperatures in autoclaved ground beef. For cells grown
at 37
◦ C, D 59 ◦ C was 3.1 minutes; cells grown at 45
◦ C had D 59 ◦ C of 7.2; and cells grown at 49
◦ C had
D 59 ◦ C of 10.6 minutes.
99 Although the wide differences in heat resistance between the two strains
noted may in part be due to strain differences, the effect of fat in the heating menstrum may also
have played a role. With beef roasts cooked in plastic bags in a water bath at 60–61
◦ C, holding
the product to an internal temperature of 60
◦ C for at least 12 minutes eliminated salmonellae and
reduced the C. perfringens population by about 3 log cycles. To effect a 12-log reduction of numbers
for roasts weighing 1.5 kg, holding at 60
◦ C for 2.3 hours or longer was necessary.
104 The thermal
destruction of C. perfringens enterotoxin in buffer and gravy at 61
◦ C required 25.4 and 23.8 minutes,
respectively.
15
Regarding the wide variations in heat resistance recorded for C. perfringens, similar variations have
not been recorded for C. botulinum, especially types A and B. The latter organisms are less common
in the human intestinal tract than C. perfringens strains. An organism inhabiting environments as
diverse as these may be expected to show wide variations among its strains. Another factor that is
important in heat resistance of bacterial spores is that of the chemical environment. Alderton and
Snell
4 pointed out that spore heat resistance is largely an inducible property, chemically reversible
between a sensitive and resistant state. Using this hypothesis, it has been shown that spores can be
made more heat resistant by treating them in calcium acetate solutions—for example, 0.1 or 0.5 M at
pH 8.5 for 140 hours at 50
◦ C. The heat resistance of endospores may be increased 5- to 10-fold by
this method.
3 On the other hand, heat resistance may be decreased by holding spores in 0.1 N HCl at
25
◦ C for 16 hours or as a result of the exposure of endospores to the natural acid conditions of some
foods. It is not inconceivable that the high variability of heat resistance of C. perfringens spores may
be a more or less direct result of immediate environmental history.
The freezing survival of C. perfringens in chicken gravy was studied by Strong and Canada,
113 who
found that only around 4% of cells survived when frozen to t17.7
◦ C for 180 days. Dried spores, on the
other hand, displayed a survival rate of about 40% after 90 days but only about 11% after 180 days.
For epidemiological studies, serotyping has been employed, but because of the many serovars, there
appears to be no consistent relationship between outbreaks and given serovars. The bacteriocin typing
of type A has been achieved, and of 90 strains involved in food outbreaks, all were typeable by a set
of eight bacteriocins and 85.6% consisted of bacteriocin types 1–6.
101
569
observed.
92 At least 13 amino acids are required for growth, along with biotin, pantothenate, pyridoxal,
adenine, and other related compounds. It is heterofermentative, and a large number of carbohydrates
are attacked. Growth is inhibited by around 5% NaCl.
The endospores of food-poisoning strains differ in their resistance to heat, with some being typical of other mesophilic spore formers and some being highly resistant. A D 100 ◦ C value of 0.31 for
C. perfringens (ATCC 3624) and a value of 17.6 for strain NCTC 8238 have been reported.
123 For
eight strains that produced reactions in rabbits, D 100 ◦ C values ranged from 0.70 to 38.37; strains that
did not produce rabbit reactions were more heat sensitive.
115 Differences in heat sensitivity among
C. perfringens strains is associated with the carriage of the cpe gene. D 100 ◦ C values for 13 meat,
poultry, and fish isolates where the cpe gene is chromosomal ranged from a low of 43 to a high of 170,
while a non-outbreak strain that carried cpe on plasmids was 3.
124 These authors noted that outbreak
strains typically possess a D 100 ◦ C >40 while non-outbreak strains are typically <2.
In view of the practice of cooking roasts in water baths for long times at low temperatures (LTLT),
the heat destruction of vegetative cells of C. perfringens has been studied by several groups. For
strain ATCC 13124 in autoclaved ground beef, D 56.8 ◦ C was 48.3 minutes, essentially similar to the
D 56.8 ◦ C or D 47.9 ◦ C for phospholipase C.
32 Employing strain NCTC 8798, D values for cells were
found to increase with increasing growth temperatures in autoclaved ground beef. For cells grown
at 37
◦ C, D 59 ◦ C was 3.1 minutes; cells grown at 45
◦ C had D 59 ◦ C of 7.2; and cells grown at 49
◦ C had
D 59 ◦ C of 10.6 minutes.
99 Although the wide differences in heat resistance between the two strains
noted may in part be due to strain differences, the effect of fat in the heating menstrum may also
have played a role. With beef roasts cooked in plastic bags in a water bath at 60–61
◦ C, holding
the product to an internal temperature of 60
◦ C for at least 12 minutes eliminated salmonellae and
reduced the C. perfringens population by about 3 log cycles. To effect a 12-log reduction of numbers
for roasts weighing 1.5 kg, holding at 60
◦ C for 2.3 hours or longer was necessary.
104 The thermal
destruction of C. perfringens enterotoxin in buffer and gravy at 61
◦ C required 25.4 and 23.8 minutes,
respectively.
15
Regarding the wide variations in heat resistance recorded for C. perfringens, similar variations have
not been recorded for C. botulinum, especially types A and B. The latter organisms are less common
in the human intestinal tract than C. perfringens strains. An organism inhabiting environments as
diverse as these may be expected to show wide variations among its strains. Another factor that is
important in heat resistance of bacterial spores is that of the chemical environment. Alderton and
Snell
4 pointed out that spore heat resistance is largely an inducible property, chemically reversible
between a sensitive and resistant state. Using this hypothesis, it has been shown that spores can be
made more heat resistant by treating them in calcium acetate solutions—for example, 0.1 or 0.5 M at
pH 8.5 for 140 hours at 50
◦ C. The heat resistance of endospores may be increased 5- to 10-fold by
this method.
3 On the other hand, heat resistance may be decreased by holding spores in 0.1 N HCl at
25
◦ C for 16 hours or as a result of the exposure of endospores to the natural acid conditions of some
foods. It is not inconceivable that the high variability of heat resistance of C. perfringens spores may
be a more or less direct result of immediate environmental history.
The freezing survival of C. perfringens in chicken gravy was studied by Strong and Canada,
113 who
found that only around 4% of cells survived when frozen to t17.7
◦ C for 180 days. Dried spores, on the
other hand, displayed a survival rate of about 40% after 90 days but only about 11% after 180 days.
For epidemiological studies, serotyping has been employed, but because of the many serovars, there
appears to be no consistent relationship between outbreaks and given serovars. The bacteriocin typing
of type A has been achieved, and of 90 strains involved in food outbreaks, all were typeable by a set
of eight bacteriocins and 85.6% consisted of bacteriocin types 1–6.
101