Determination of histamine and histamine-forming bacteria in tuna dumpling implicated in a food-borne poisoning

An incident of food-borne poisoning causing illness in seven victims, due to ingestion of tuna dumpling, occurred in March 2006, in Chiayi Prefecture, southern Taiwan. The leftovers of the victims’ tuna dumpling and the five other tuna dumpling samples from five other retail stores were collected and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, aerobic plate count (APC), total volatile basic nitrogen (TVBN), total coliform (TC) and Escherichia coli in all samples ranged from 6.08 to 6.43, 0.46% to 0.81%, 5.90 to 8.95 log CFU/g, 6.38 to 21.29 mg/100 g, 750 to 8000 most probable number (MPN)/g, and <3 to 1000 MPN/g, respectively. The suspected tuna dumpling contained 160.8 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 tuna dumpling, this food-borne poisoning was strongly suspected to be due to histamine intoxication. In addition, although thirteen histamine-producing bacteria strains capable of producing 8.1–19.7 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH), were identified as Enterobacter sp. (three strains), Pantoea agglomerans (two strains), Klebsiella variicola (four strains) and Serratia marcescens (four strains), by 16S rDNA sequencing with PCR amplification, they were not determined to be the main contributors to histamine accumulation in suspected tuna dumpling.