Histamine Production by Photobacterium spp. in Tuna and Mahi-Mahi under Various Storage Temperatures

Histamine-producing bacteria (HPB) generate histamine in decomposing scombrotoxin-forming fish tissue. Elevated histamine levels (≥200 ppm) can cause scombrotoxin fish poisoning in humans who consume decomposed fish and fishery products. In this study, four psychrotrophic Photobacterium species, P. kishitanii, P. angustum, P. aquimaris, and P. phosphoreum, were evaluated in pure culture for histamine production at 4, 10, and 20 °C. P. kishitanii and P. angustum demonstrated the most prolific histamine production in vitro and were inoculated into tuna and mahi-mahi tissue to determine the time at which histamine exceeded FDA guidance levels at 4 and 10 °C for P. kishitanii and 10 and 20 °C for P. angustum. Current U.S. FDA guidance levels for histamine are ≥200 ppm for human health hazard and ≥35 ppm for evidence of decomposition. Samples were analyzed for histamine with a modified AOAC fluorometric method. Tuna inoculated at 10², 10⁴, and 10⁶ CFU/g P. kishitanii, accumulated histamine levels ≥200 ppm after 7, 5, and 3 days at 4 °C and 2, 2, and 1 day(s) at 10 °C, respectively. Tuna inoculated at 10², 10⁴, and 10⁶ CFU/g P. angustum, contained histamine levels ≥200 ppm after 6, 4, and 2 days at 10 °C and 24, 20, and 12 h at 20 °C, respectively. Mahi-mahi inoculated at 10², 10⁴, and 10⁶ CFU/g P. kishitanii accumulated histamine levels ≥200 ppm after 9, 6, and 4 days at 4 °C and 3, 3, and 2 days at 10 °C, respectively. Mahi-mahi inoculated at 10², 10⁴, and 10⁶ CFU/g P. angustum contained histamine levels ≥200 ppm after 10, 9, and 3 days at 10 °C and 38, 16, and 12 h at 20 °C, respectively. Tissues contained ≥200 ppm histamine after 3-9 days under storage temperature of 4 °C, but as early as 12 h when held at elevated temperatures. Understanding how storage conditions affect HPB growth and histamine production in scombrotoxin-forming fish is important to inform guidance for recommended fish storage conditions and to mitigate risks.