Histamine in fish is formed from
Answer: C
Correct answer: histidine
Bacterial histidine decarboxylase removes the carboxyl group from free histidine to give histamine. The reaction requires the amino acid to be present in quantity, which is why only certain fish families are implicated - the enzyme cannot make histamine from a substrate the fish does not contain.
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The bacterial enzyme responsible for histamine formation is
Answer: D
Decarboxylases released by microorganisms remove the carboxyl group from free histidine. The enzyme comes from the bacteria rather than from the fish itself, which is why the hazard depends on how heavily the fish is contaminated and how long it stays warm.
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Which organism is named as a histamine producer in fish?
Answer: A
Correct answer: Morganella morganii
Morganella morganii is the classic histamine former, carrying a highly active histidine decarboxylase. It is an enteric organism found in the gut and on the skin of fish, and it produces histamine rapidly at abuse temperatures, which is why time out of chill is the critical factor.
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Histamine-producing bacteria in fish are found chiefly
Answer: B
Correct answer: in the intestine or on the skin
The organisms live on the outside and in the gut of the live fish, and the flesh of a healthy fish is essentially sterile. Histamine formation therefore begins at those surfaces and works inward, which is why prompt gutting and chilling are the standard controls.
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Once histamine has formed in fish, it
Answer: C
Correct answer: is not destroyed by cooking
Histamine is a small, heat-stable molecule that survives cooking, canning, smoking and freezing entirely. This is what makes scombroid poisoning different from a bacterial infection: killing the organisms achieves nothing once the toxin is formed, so the only control is preventing its formation in the first place.
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Histamine formation is greatest at temperatures
Answer: D
Correct answer: near 32.2 degrees Celsius
Histamine formation is fastest at ambient tropical temperatures, around 32 degrees, where the decarboxylase-producing bacteria multiply most rapidly. A tuna left on a warm deck for a few hours can become hazardous, which is why chilling immediately on capture is the single most important control.
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Frozen storage that stops bacterial growth and enzyme activity is at
Answer: A
Correct answer: minus 18 degrees Celsius or below
Minus 18 is the conventional frozen storage standard, at which no microbial growth occurs and enzymic and chemical change proceeds so slowly as to be negligible over normal storage periods. Warmer frozen temperatures allow gradual quality loss even though the food remains microbiologically safe.
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Why can histamine continue to accumulate in chilled fish?
Answer: B
Correct answer: Preformed enzyme stays active near refrigeration temperature
This is the sting in the tail of histamine control. Even after chilling stops the bacteria growing, the histidine decarboxylase they have already produced continues to work, slowly, at refrigeration temperature. Fish that has been temperature-abused and then chilled therefore keeps accumulating histamine, which is why the abuse cannot be undone.
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Which organism can produce toxic histamine levels at temperatures as low as 0 degrees Celsius?
Answer: C
Correct answer: Morganella psychrotolerans
As its name indicates, Morganella psychrotolerans grows at chill temperatures and can generate hazardous histamine levels at around zero degrees. Its recognition changed the understanding of the hazard: correct chilling slows histamine formation greatly but does not guarantee its prevention over a long storage life.
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Which fish family is most associated with histamine poisoning?
Answer: D
Scombridae, which includes tuna and mackerel, heads the list of families with high free histidine, alongside Clupeidae, Engraulidae, Coryphaenidae and Pomatomidae. The condition is named scombrotoxin poisoning after them.
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