Photobacterium angustum and Photobacterium kishitanii, Psychrotrophic High-Level Histamine-Producing Bacteria Indigenous to Tuna

Scombrotoxin fish poisoning (SFP) remains the main contributor of fish poisoning incidents in the United States, despite efforts to control its spread. Psychrotrophic histamine-producing bacteria (HPB) indigenous to scombrotoxin-forming fish may contribute to the incidence of SFP. We examined the gills, skin, and anal vents of yellowfin (n = 3), skipjack (n = 1), and albacore (n = 6) tuna for the presence of indigenous HPB. Thirteen HPB strains were isolated from the anal vent samples from albacore (n = 3) and yellowfin (n = 2) tuna. Four of these isolates were identified as Photobacterium kishitanii and nine isolates as Photobacterium angustum; these isolates produced 560 to 603 and 1,582 to 2,338 ppm histamine in marine broth containing 1% histidine (25 degrees C for 48 h), respectively. The optimum growth temperatures and salt concentrations were 26 to 27 degrees C and 1% salt for P. kishitanii and 30 to 32 degrees C and 2% salt for P. angustum in Luria 70% seawater (LSW-70). The optimum activity of the HDC enzyme was at 15 to 30 degrees C for both species. At 5 degrees C, P. kishitanii and P. angustum had growth rates of 0.1 and 0.2 h(-1\), respectively, and the activities of histidine decarboxylase (HDC) enzymes were 71% and 63%, respectively. These results show that indigenous HPB in tuna are capable of growing at elevated and refrigeration temperatures. These findings demonstrate the need to examine the relationships between the rate of histamine production at refrigeration temperatures, seafood shelf life, and regulatory limits.