374 ◾ Fundamental Food Microbiology
foods listed, protein-rich foods were involved in high percentages. The three most important contributing factors in these outbreaks, in order of importance, were improper holding temperature,
inadequate cooking, and contaminated equipment. The most important predisposing cause was
cooking food in large volumes in advance, allowing it to cool slowly, then holding for a long period
and often serving without reheating. Cooking kills the vegetative cells, but the spores survive.
Large volumes of the food provide an anaerobic environment, and slow cooling not only provides
the temperature for the spores to germinate and outgrow but also allows cells to multiply rapidly to
reach high population levels before eating. The food may not show any loss of acceptance quality.
Prevention 6
The presence of Clo. perfringens spores and cells in foods is not uncommon. Unless viable cells are
present in high numbers before eating, they cannot cause gastroenteritis; thus, the aim is to keep
the cell numbers low. This can be achieved by using proper sanitation in all phases of food preparation and handling. Food should be cooked to the highest temperature recommended to kill the
cells and as many spores as possible. The food should be cooled quickly and uniformly (preferably
within one hour) to refrigerated temperature. A shallow container, in contrast to a deep container,
facilitates rapid cooling (below 10°C or 50°F). If a food is stored for a long time, it is important
to reheat it quickly and uniformly (to kill vegetative cells) and keep it hot (above 60°C or 140°F)
while being served.
Detection Method
The detection method involves enumeration of the incriminated food and fecal samples for Clo.
perfringens in a selective agar medium and incubation of plates under anaerobic conditions.
table 27.1 Food types involved in Clo. perfringens
outbreaks from 1973 to 1987 in the United States
Food Types
No. of Outbreaks a
%
Beef
51
26.3
Mexican foods
23
11.9
Turkey
19
9.8
Chicken
9
4.6
Pork
8
4.1
Finfish
3
1.6
Shellfish
2
1.0
Vegetables
1
0.5
Others
46
23.8
Unknown
28
14.4
a Total cases were 12,234.
foods listed, protein-rich foods were involved in high percentages. The three most important contributing factors in these outbreaks, in order of importance, were improper holding temperature,
inadequate cooking, and contaminated equipment. The most important predisposing cause was
cooking food in large volumes in advance, allowing it to cool slowly, then holding for a long period
and often serving without reheating. Cooking kills the vegetative cells, but the spores survive.
Large volumes of the food provide an anaerobic environment, and slow cooling not only provides
the temperature for the spores to germinate and outgrow but also allows cells to multiply rapidly to
reach high population levels before eating. The food may not show any loss of acceptance quality.
Prevention 6
The presence of Clo. perfringens spores and cells in foods is not uncommon. Unless viable cells are
present in high numbers before eating, they cannot cause gastroenteritis; thus, the aim is to keep
the cell numbers low. This can be achieved by using proper sanitation in all phases of food preparation and handling. Food should be cooked to the highest temperature recommended to kill the
cells and as many spores as possible. The food should be cooled quickly and uniformly (preferably
within one hour) to refrigerated temperature. A shallow container, in contrast to a deep container,
facilitates rapid cooling (below 10°C or 50°F). If a food is stored for a long time, it is important
to reheat it quickly and uniformly (to kill vegetative cells) and keep it hot (above 60°C or 140°F)
while being served.
Detection Method
The detection method involves enumeration of the incriminated food and fecal samples for Clo.
perfringens in a selective agar medium and incubation of plates under anaerobic conditions.
table 27.1 Food types involved in Clo. perfringens
outbreaks from 1973 to 1987 in the United States
Food Types
No. of Outbreaks a
%
Beef
51
26.3
Mexican foods
23
11.9
Turkey
19
9.8
Chicken
9
4.6
Pork
8
4.1
Finfish
3
1.6
Shellfish
2
1.0
Vegetables
1
0.5
Others
46
23.8
Unknown
28
14.4
a Total cases were 12,234.