Final answer:
Food poisoning from preformed exotoxins is characterized by rapid symptom onset and can be diagnosed by detecting the exotoxin in food or biological specimens. Exotoxins are heat labile proteins, but some can resist boiling temperatures and cause food intoxication.
Step-by-step explanation:
You can tell when food poisoning comes from a preformed exotoxin by the rapid onset of signs and symptoms such as nausea, vomiting, and diarrhea, often occurring within a few hours after consuming the contaminated food. The diagnosis is confirmed by identifying the preformed exotoxin in the food sample or in biological specimens like feces or vomitus using serological techniques such as ELISA. Unlike endotoxins, exotoxins are protein molecules that are secreted by bacteria and can act very quickly. Some exotoxins are heat labile and can produce symptoms even if the bacteria that produced them are no longer present. Certain exotoxins, like Staphylococcal enterotoxins which cause food intoxication, are heat stable and can survive even boiling temperatures. Therefore, thorough cooking does not always prevent food poisoning by preformed exotoxins.