372 ◾ Fundamental Food Microbiology
in more than 7% of the total foodborne outbreaks and more than 10% of the total number of
cases. In the 1980s, the incidence dropped to approximately 3% of the total outbreaks, affecting approximately 5% of the total cases. The outbreaks generally occurred with some foods that
were prepared in advance by heating and then kept warm for several hours before serving. In the
majority of the instances, these situations were associated with feeding many people within a short
period of time in cafeterias, restaurants, schools, and banquets (banquet disease). Between 1983
and 1987, out of 24 outbreaks, 12 were associated with such institutions and only one outbreak
occurred with food prepared at home. Between 1993 and 1997, there were 57 outbreaks with 2772
cases. In 2009 and 2010, there were a total of 57 outbreaks associated with Clo. perfringens in the
United States, affecting over 3000 people. 2 It is now estimated that this pathogen causes approximately 960,000 cases with 26 deaths annually in the United States. 3 As the disease produces mild
symptoms, many incidents are probably not reported. Thus, the reported cases could be only a
fraction of the actual numbers and the annual estimates are 248,520 cases.
Characteristics
The cells are gram-positive, motile rods, and are spore-formers. Cells vary in size and can form
small chains. Clo. perfringens is anaerobic but can tolerate some air (oxygen). The vegetative cells
are sensitive to low-heat treatment (pasteurization), but the spores are extremely heat resistant,
and some can survive even boiling for several hours. The cells are resistant to D-cycloserine. In
the presence of suitable substrates, H 2 S is formed during growth. The cells need several amino
acids for growth. Thus, they can grow very effectively in many protein foods. The temperatures
of growth of vegetative cells and germination of spores and outgrowth range between 10°C and
52°C. The optimum growth occurs at approximately 45°C. At optimum conditions, cell multiplication can be very rapid, in approximately nine minutes. The cells fail to grow well at pH < 5.0, in
NaCl concentrations > 5%, A W < 0.93, and in 500 ppm nitrite.
Habitat
Spores and vegetative cells are found in soil; dust; the intestinal contents of animals, birds, and
humans; and sewage. Many foods, particularly raw foods, get contaminated from these sources.
Toxins and Toxin Production
There are five types of Clo. perfringens (A, B, C, D, and E) based on the production of four types of
extracellular toxins (alpha, beta, epsilon, and iota). Type A strains are predominantly involved in
foodborne toxico-infection. Clo. perfringens enterotoxin (CPE), a 34-kDa protein that is associated
with the foodborne disease, is a heat-labile protein. Enterotoxin production is encoded by the cpe
gene located in a plasmid or in the chromosome. CPE is an intracellular protein produced by the
cells during sporulation in the intestine and released. Unlike toxins of food-poisoning microorganisms, the enterotoxin is produced in the digestive tract during sporulation. The environmental
parameters for the production of enterotoxin are directly related to the sporulation environment.
Figure 27.1 shows sequential events that lead to enterotoxin (CPE) production and clostridial food
poisoning. There are some reports that, in addition to the intestine, sporulation and enterotoxin
production to certain levels can also occur in some foods.
in more than 7% of the total foodborne outbreaks and more than 10% of the total number of
cases. In the 1980s, the incidence dropped to approximately 3% of the total outbreaks, affecting approximately 5% of the total cases. The outbreaks generally occurred with some foods that
were prepared in advance by heating and then kept warm for several hours before serving. In the
majority of the instances, these situations were associated with feeding many people within a short
period of time in cafeterias, restaurants, schools, and banquets (banquet disease). Between 1983
and 1987, out of 24 outbreaks, 12 were associated with such institutions and only one outbreak
occurred with food prepared at home. Between 1993 and 1997, there were 57 outbreaks with 2772
cases. In 2009 and 2010, there were a total of 57 outbreaks associated with Clo. perfringens in the
United States, affecting over 3000 people. 2 It is now estimated that this pathogen causes approximately 960,000 cases with 26 deaths annually in the United States. 3 As the disease produces mild
symptoms, many incidents are probably not reported. Thus, the reported cases could be only a
fraction of the actual numbers and the annual estimates are 248,520 cases.
Characteristics
The cells are gram-positive, motile rods, and are spore-formers. Cells vary in size and can form
small chains. Clo. perfringens is anaerobic but can tolerate some air (oxygen). The vegetative cells
are sensitive to low-heat treatment (pasteurization), but the spores are extremely heat resistant,
and some can survive even boiling for several hours. The cells are resistant to D-cycloserine. In
the presence of suitable substrates, H 2 S is formed during growth. The cells need several amino
acids for growth. Thus, they can grow very effectively in many protein foods. The temperatures
of growth of vegetative cells and germination of spores and outgrowth range between 10°C and
52°C. The optimum growth occurs at approximately 45°C. At optimum conditions, cell multiplication can be very rapid, in approximately nine minutes. The cells fail to grow well at pH < 5.0, in
NaCl concentrations > 5%, A W < 0.93, and in 500 ppm nitrite.
Habitat
Spores and vegetative cells are found in soil; dust; the intestinal contents of animals, birds, and
humans; and sewage. Many foods, particularly raw foods, get contaminated from these sources.
Toxins and Toxin Production
There are five types of Clo. perfringens (A, B, C, D, and E) based on the production of four types of
extracellular toxins (alpha, beta, epsilon, and iota). Type A strains are predominantly involved in
foodborne toxico-infection. Clo. perfringens enterotoxin (CPE), a 34-kDa protein that is associated
with the foodborne disease, is a heat-labile protein. Enterotoxin production is encoded by the cpe
gene located in a plasmid or in the chromosome. CPE is an intracellular protein produced by the
cells during sporulation in the intestine and released. Unlike toxins of food-poisoning microorganisms, the enterotoxin is produced in the digestive tract during sporulation. The environmental
parameters for the production of enterotoxin are directly related to the sporulation environment.
Figure 27.1 shows sequential events that lead to enterotoxin (CPE) production and clostridial food
poisoning. There are some reports that, in addition to the intestine, sporulation and enterotoxin
production to certain levels can also occur in some foods.