Purpose: The objective of this study was to examine the prevalence and distribution of high-HPB in SF fish from the Gulf of Mexico.
Methods: Gill, skin, and intestine swabs from 54 SF fish were enriched in histidine broth (tryptic soy broth with 1% histidine, 1.5 % NaCl) for 24 h at 30°C. Enrichments were analyzed for total and species-specific HPB by real-time PCR. HPB were isolated and confirmed from positive samples and their histamine production was measured. Photobacterium damselae and M. morganii histamine production was further compared in ground tuna inoculated at 5.5 log MPN/g for 8 h at 30°C.
Results: P. damselae (102/162) was most frequently detected followed by M. morganii (34/162), Enterobacter aerogenes (10/162), and Raoultella planticola (4/162). P. damselae and M. morganii were detected in gills (30/54, 6/54), intestine (31/54, 11/54), and skin (41/54, 17/54) but E. aerogenes and R. planticola were infrequently detected on skin (6/54, 2/54) and gills (4/54, 2/54). P. damselae, M. morganii, E. aerogenes, and R. planticola isolates produced on average 3063, 4111, 4687, and 4872 ppm histamine after 48 h in histidine broth at 30°C. Finally, P. damselae produced significantly higher histamine (1031 ppm, P = 0.041) and grew to a significantly higher density (8.4 log MPN/g, P = 0.050) in ground tuna compared to M. morganii (98.5 ppm; 7.3 log MPN/g) after 8 h at 30°C.
Significance: Using newly developed molecular methods, we found that P. damselae was more frequently detected in SF fish from Gulf of Mexico and produced more histamine in tuna muscle than M. morganii. This HPB is a significant concern and should be accounted for in the control of scombrotoxin poisoning.