Determination of histamine and histamine-forming bacteria in dried milkfish (Chanos chanos) implicated in a food-borne poisoning

An incident of food-borne poisoning, causing illness in three victims due to ingestion of dried milkfish, occurred in February, 2006, in Tainan Prefecture, southern Taiwan. The leftovers of the victims’ dried milkfish and three other dried milkfish samples, from the same retail store as the leftover fish, were collected and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, aerobic plate count (APC) and total volatile basic nitrogen (TVBN) in the leftover dried milkfish sample were significantly higher than those of the other three milkfish samples. None of the tested milkfish samples contained total coliform and Escherichia coli. Although the histamine contents in the three other milkfish samples were less than 5 mg/100 g, the suspected milkfish sample contained 61.6 mg/100 g of histamine, which is greater than the hazard action level of 50 mg/100 g. Given the allergy-like symptoms of the victims and the high histamine content in the suspected milkfish sample, this food-borne poisoning was strongly suspected to be due to histamine intoxication. Four histamine-producing bacterial strains, capable of producing 11.9–1243 ppm of histamine in trypticase soy broth supplemented with 1.0% l-histidine (TSBH), were identified as Staphylococcus sciuri subsp. sciuri, Serratia grimesii, Bacillus cereus and Raoultella ornithinolytica, by 16S rDNA sequencing with PCR amplification. R. ornithinolytica was a potent histamine-former capable of producing more than 800 ppm of histamine in TSBH in the presence of 1.5% or 3.5% NaCl. Therefore, R. ornithinolytica could be the causative bacterium responsible for the production of high content of histamine that eventually led to this dried milkfish poisoning incident.