328 ◾ Fundamental Food Microbiology
Identification Methods
To associate a food implicated in staphylococcal food poisoning, the food, or foods, or vomit
samples are analyzed for the presence of high levels of enterotoxigenic Sta. aureus cells and
enterotoxin(s) (Chapter 42). An enumeration technique in one or more selective differential agar
media to determine the load of viable cells of Sta. aureus followed by several biochemical tests,
such as hemolysis, coagulase, thermonuclease reactions, or ability of a pure culture to produce
enterotoxin, are performed to link the potential causes of the food poisoning outbreaks.
The enterotoxin(s) from the food or vomit samples are extracted and tested, either by biological means or by serological means, to associate them with the outbreak. In the biological method,
animals (such as cats, monkeys, or dogs) are given the enterotoxin preparation orally or injected
intraperitoneally or intravenously. Vomiting symptoms by the test animals is a positive indication
of the presence of staphylococcal enterotoxin.
In serological methods, the enterotoxins are purified and examined by one of the several recommended immunological methods. Not only are these tests very sensitive, but they also allow the
identification of the types of enterotoxins involved in a food poisoning case.
Analysis of an Outbreak
A foodborne disease outbreak affecting 52 of 101 people who attended a dinner (foods prepared
at home) was reported on December 6, 1986, in Riverton, Wyoming. Of these, 49 people needed
immediate medical attention. The symptoms developed between less than one to seven hours after
the meal and included nausea (100%), vomiting (98%), diarrhea (90%), abdominal cramps (83%),
prostration (62%), chills (52%), sweating (35%), and blood pressure–temperature depression
(21%). When the regulatory people came to investigate after 36 hours, samples of foods or vomit
of the patients from the doctors were not available. However, one vomit sample frozen by a patient
was available and, when analyzed, was found to have 12–19 × 10 6 per gram coagulase-positive Sta.
aureus. Meat obtained from a leftover turkey carcass had 1 × 10 6 per gram coagulase-positive Sta.
aureus. An investigation revealed that a person who deboned and handled the cooked turkey had
erupting facial rash (acneiform). The turkeys (three total) were improperly cooled following cooking and held on an improperly heated steam table for about four hours prior to serving.
This is a classical case of a staphylococcal food poisoning outbreak in which more than half of
the people who ate foods involving several preparations developed many of the classical symptoms,
some within 30 minutes. Although the food samples served in the dinner or vomit samples from
the attending physicians or medical facilities were not available, analysis of a vomit sample saved
by a patient revealed the presence of very high numbers of coagulase-positive Sta. aureus and meat
available from a leftover turkey carcass also had fairly large numbers of Sta. aureus. So, from the
symptoms and indirect evidence, the outbreak was concluded to be an incidence of staphylococcal
food poisoning.
The sequences of events were most likely as follows: The erupting facial rash of the food handler was most probably the source of the pathogen. The pathogen was transmitted by the individual through the hands during the deboning of the cooked turkey. Sta. aureus is capable of growing
in meat under a suitable environment. The turkey, following cooking and prior to serving, was
temperature abused for a long period of time, thus enabling the contaminants to grow and reach
very high populations. However, the acceptance quality of the meat was not adversely affected.
The stage was set and many consumed enough toxin with turkey (and could be with other servings
also) to develop the symptoms.
Identification Methods
To associate a food implicated in staphylococcal food poisoning, the food, or foods, or vomit
samples are analyzed for the presence of high levels of enterotoxigenic Sta. aureus cells and
enterotoxin(s) (Chapter 42). An enumeration technique in one or more selective differential agar
media to determine the load of viable cells of Sta. aureus followed by several biochemical tests,
such as hemolysis, coagulase, thermonuclease reactions, or ability of a pure culture to produce
enterotoxin, are performed to link the potential causes of the food poisoning outbreaks.
The enterotoxin(s) from the food or vomit samples are extracted and tested, either by biological means or by serological means, to associate them with the outbreak. In the biological method,
animals (such as cats, monkeys, or dogs) are given the enterotoxin preparation orally or injected
intraperitoneally or intravenously. Vomiting symptoms by the test animals is a positive indication
of the presence of staphylococcal enterotoxin.
In serological methods, the enterotoxins are purified and examined by one of the several recommended immunological methods. Not only are these tests very sensitive, but they also allow the
identification of the types of enterotoxins involved in a food poisoning case.
Analysis of an Outbreak
A foodborne disease outbreak affecting 52 of 101 people who attended a dinner (foods prepared
at home) was reported on December 6, 1986, in Riverton, Wyoming. Of these, 49 people needed
immediate medical attention. The symptoms developed between less than one to seven hours after
the meal and included nausea (100%), vomiting (98%), diarrhea (90%), abdominal cramps (83%),
prostration (62%), chills (52%), sweating (35%), and blood pressure–temperature depression
(21%). When the regulatory people came to investigate after 36 hours, samples of foods or vomit
of the patients from the doctors were not available. However, one vomit sample frozen by a patient
was available and, when analyzed, was found to have 12–19 × 10 6 per gram coagulase-positive Sta.
aureus. Meat obtained from a leftover turkey carcass had 1 × 10 6 per gram coagulase-positive Sta.
aureus. An investigation revealed that a person who deboned and handled the cooked turkey had
erupting facial rash (acneiform). The turkeys (three total) were improperly cooled following cooking and held on an improperly heated steam table for about four hours prior to serving.
This is a classical case of a staphylococcal food poisoning outbreak in which more than half of
the people who ate foods involving several preparations developed many of the classical symptoms,
some within 30 minutes. Although the food samples served in the dinner or vomit samples from
the attending physicians or medical facilities were not available, analysis of a vomit sample saved
by a patient revealed the presence of very high numbers of coagulase-positive Sta. aureus and meat
available from a leftover turkey carcass also had fairly large numbers of Sta. aureus. So, from the
symptoms and indirect evidence, the outbreak was concluded to be an incidence of staphylococcal
food poisoning.
The sequences of events were most likely as follows: The erupting facial rash of the food handler was most probably the source of the pathogen. The pathogen was transmitted by the individual through the hands during the deboning of the cooked turkey. Sta. aureus is capable of growing
in meat under a suitable environment. The turkey, following cooking and prior to serving, was
temperature abused for a long period of time, thus enabling the contaminants to grow and reach
very high populations. However, the acceptance quality of the meat was not adversely affected.
The stage was set and many consumed enough toxin with turkey (and could be with other servings
also) to develop the symptoms.