Determination of histamine and bacterial isolation in swordfish fillets (Xiphias gladius) implicated in a food borne poisoning

An incident of food borne poisoning causing illness in 43 victims due to ingestion of swordfish fillets occurred in December, 2004, in Taichung Prefecture, central Taiwan. Eight frozen raw swordfish fillets were collected from the suspected restaurant and analyzed for bacterial content and histamine-related quality. The levels of aerobic plate count, total coliform, and total volatile basic nitrogen in all samples ranged from 5.39 to 6.71 log CFU/g, <3–1360 most probable number (MPN)/g, and 6.44–14.56 mg/100 g, respectively. None of these samples contained Escherichia coli. The suspected swordfish fillets contained 85.9–293.7 mg/100 g of histamine greater than the hazard action level of 50 mg/100 g set by the US. Food and Drug Administration (FDA) for tuna fish. Given the allergy-like symptoms of the victims and the high histamine content in the suspected swordfish fillets, this food borne poisoning was strongly suspected to be due to histamine intoxication. In addition, although ten histamine-producing bacteria strains, capable of producing 12.7–33.0 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine, were identified as Staphylococcus sp. (one strain), S. aureus (two strains) and S. aureus subsp. aureus (seven strains), by 16S rDNA sequencing with PCR amplification, they were not determined to be the main contributors to histamine accumulation in suspected swordfish fillets.