Foodborne Intoxications ◾ 325
of NO 2 . However, their growth can be reduced by combining two or more parameters. Because
of their ability to grow under several adverse conditions, Sta. aureus can grow in many foods.
Normally, they are poor competitors in the presence of many other microorganisms found in
foods. But their ability to grow under adverse environments gives them an edge in growth in many
foods where others do not grow favorably.
Habitat
Enterotoxin-producing Sta. aureus strains have generally been associated with staphylococcal food
intoxication. Although strains of several other Staphylococcus species are known to be enterotoxin
producers, their involvement in food poisoning is not fully known. Sta. aureus, along with many
other staphylococci, are naturally present in the nose, throat, skin, and hair (feathers) of healthy
humans, animals, and birds. Sta. aureus can be present in infections, such as cuts in skin and
abscesses (boils, carbuncles) in humans, animals, and birds, and cuts in hands and facial erupted
acne in humans. Food contamination generally occurs from these sources.
Toxins and Toxin Production
Enterotoxigenic strains of Sta. aureus produce 21 different enterotoxins: A, B, C1, C2, C3, D,
and E through V (also designated as SEA, SEB, etc.). They are serologically distinct, heat-stable
proteins of molecular weight 26–30 kDa and differ in toxicity. Toxins are water soluble and may
be resistant to proteolytic enzymes. The genes encoding enterotoxin production are present in prophage, plasmids, pathogenicity islands, enterotoxin gene cluster (egc) and staphylococcal cassette
chromosome (SCC). Toxins are produced when the food, primarily protein-rich food, is left at
room temperature for long periods. The toxins vary in heat stability. Generally, they can withstand
a temperature of 60°C for 16 hours. SEB is more stable than SEA, and it has been considered as
a potential weapon in bioterrorism. 4 Normal temperature and time used in processing or cooking foods will not destroy the potency of the toxins. Outbreaks from SEA are more frequent; one
reason could be because of its high potency.
The rate of toxin production by a strain is directly related to its rate of growth and cell concentrations. Optimum growth occurs around 37°C–40°C. Under optimum conditions of growth,
toxins can be detected when a population has reached over a few million per gram or milliliter
of food and generally in about four hours. Some of the lowest environmental parameters of toxin
production are 10°C, pH 5.0, or A W 0.86. However, by combining two or more parameters, the
lowest ranges can be adversely affected.
Disease and Symptoms
Staphylococcal toxins are enteric toxins and cause gastroenteritis. A healthy adult has to consume
about 30 g or mL of a food containing 100–200 ng toxins produced by 10 6 –10 7 cells per gram or
milliliter; infants and old and sick individuals need less. Upon consumption, the toxin stimulates
the vagus nerve in the stomach and induces severe vomiting (Figure 25.2). The symptoms occur
within two to four hours with a range of 30 minutes to eight hours and are directly related to the
potency and amounts of toxin ingested and an individual’s resistance. The disease lasts for about
one to two days and is rarely fatal and only six deaths are reported to occur annually in the United
States.
of NO 2 . However, their growth can be reduced by combining two or more parameters. Because
of their ability to grow under several adverse conditions, Sta. aureus can grow in many foods.
Normally, they are poor competitors in the presence of many other microorganisms found in
foods. But their ability to grow under adverse environments gives them an edge in growth in many
foods where others do not grow favorably.
Habitat
Enterotoxin-producing Sta. aureus strains have generally been associated with staphylococcal food
intoxication. Although strains of several other Staphylococcus species are known to be enterotoxin
producers, their involvement in food poisoning is not fully known. Sta. aureus, along with many
other staphylococci, are naturally present in the nose, throat, skin, and hair (feathers) of healthy
humans, animals, and birds. Sta. aureus can be present in infections, such as cuts in skin and
abscesses (boils, carbuncles) in humans, animals, and birds, and cuts in hands and facial erupted
acne in humans. Food contamination generally occurs from these sources.
Toxins and Toxin Production
Enterotoxigenic strains of Sta. aureus produce 21 different enterotoxins: A, B, C1, C2, C3, D,
and E through V (also designated as SEA, SEB, etc.). They are serologically distinct, heat-stable
proteins of molecular weight 26–30 kDa and differ in toxicity. Toxins are water soluble and may
be resistant to proteolytic enzymes. The genes encoding enterotoxin production are present in prophage, plasmids, pathogenicity islands, enterotoxin gene cluster (egc) and staphylococcal cassette
chromosome (SCC). Toxins are produced when the food, primarily protein-rich food, is left at
room temperature for long periods. The toxins vary in heat stability. Generally, they can withstand
a temperature of 60°C for 16 hours. SEB is more stable than SEA, and it has been considered as
a potential weapon in bioterrorism. 4 Normal temperature and time used in processing or cooking foods will not destroy the potency of the toxins. Outbreaks from SEA are more frequent; one
reason could be because of its high potency.
The rate of toxin production by a strain is directly related to its rate of growth and cell concentrations. Optimum growth occurs around 37°C–40°C. Under optimum conditions of growth,
toxins can be detected when a population has reached over a few million per gram or milliliter
of food and generally in about four hours. Some of the lowest environmental parameters of toxin
production are 10°C, pH 5.0, or A W 0.86. However, by combining two or more parameters, the
lowest ranges can be adversely affected.
Disease and Symptoms
Staphylococcal toxins are enteric toxins and cause gastroenteritis. A healthy adult has to consume
about 30 g or mL of a food containing 100–200 ng toxins produced by 10 6 –10 7 cells per gram or
milliliter; infants and old and sick individuals need less. Upon consumption, the toxin stimulates
the vagus nerve in the stomach and induces severe vomiting (Figure 25.2). The symptoms occur
within two to four hours with a range of 30 minutes to eight hours and are directly related to the
potency and amounts of toxin ingested and an individual’s resistance. The disease lasts for about
one to two days and is rarely fatal and only six deaths are reported to occur annually in the United
States.