Histamine—forming Bacteria Isolated From Spoiled Skipjack Tuna and Jack Mackerel

Bacterial isolates from spoiled skipjack tuna and jack mackerel were examined for their ability to produce histamine in tuna infusion broth. Thirty‐one percent of the 470 isolates produced from 0.10 mg/ml to 4.0 mg/ml of histamine in broth. Forty‐four of these isolates were tentatively identified as: Proteus morganii (21); Hafnia alvei (13); Proteus species (3); Klebsiella species (1); and unknown (6). Histamine (0.05M) did not inhibit histidine decarboxylase activity, but repressed histidine decarboxylase formation with one strain of Proteus morganii in a synthetic medium.