SEAFOODplus: Major breakthrough in fighting histamine poisoning

Scientific Alert Note

Major breakthrough in fighting histamine poisoning

Histamine fish poisoning is caused by eating seafood in which bacteria have produced high concentrations of histamine. The BIOCOM project (project 3.4) has identified a new bacterium that can grow and produce toxic concentrations of histamine at temperatures as low as 2°C. We have called this new bacterium Morganella psychrotolerans due to its important abilities to grow and form histamine in chilled seafood. In August 2006 Jette Emborg from DIFRES presented the identification of this new bacterium at a major international food safety conference in Canada (IAFP 2006). Her presentation won an award in the developing scientist competition.

Authors: Paw Dalgaard, BIOCOM project leader pad(at)difres.dk and Jette Emborg, Ph.D. student jem(at)difres.dk

A more detailed description of this new and important bacterium is published in October 2006 (Emborg, J., Dalgaard, P., & Ahrens, P., "Morganella psychrotolerans sp. nov. a histamine-producing bacterium isolated from various seafoods", International Journal of Systematic and Evolutionary Microbiology. 56, 2473-2479). Morganella psychrotolerans has been identified as a new species by determining both molecular and phenotypic characteristics. The sequencing of fragments from seven different genes (multi locus sequencing) has been particularly valuable. At DIFRES we are very pleased with the results. In fact, this is the first time we have identified a new bacterial species of direct importance to seafood safety.

: Sequencing of fragments from seven different genes clearly showed Morganella psychrotolerans to differ from the well known bacterium Morganella morganii

The overall aim of the BIOCOM project is to reduce histamine fish poisoning caused by eating seafood. BIOCOM has carefully studied seafoods involved in 16 different outbreaks of histamine fish poisoning. What is interesting is that psychrotolerant bacteria have been responsible for the formation of histamine in several of the seafoods that actually caused histamine fish poisoning. So it is important to identify these bacteria and to determine what storage conditions and product characteristics can prevent their histamine formation in seafood.

In the case of Morganella psychrotolerans a modified atmosphere packaging has been identified that can significantly reduce histamine formation as opposed to vacuum packaging. This innovation is particularly important for fresh and lean tuna loins (Int. J. Food Microbiol. 2005, 101, 263-279). For sliced and vacuum-packed cold-smoked tuna, the addition of salt can be used to limit histamine formation by Morganella psychrotolerans and the required concentration has been determined by the BIOCOM project (J. Food Prot. 2006, 69, 4, 897-906).

: Morganella psychrotolerans can be detected as small red colonies when using the so-called VRBG agar medium. As shown in the left part of the picture above, other enterobacteriaceae bacteria form larger red colonies in this medium.

Together with Photobacteroum phosphoreum, Morganella psychrotolerans belongs to the psychro-tolerant and strongly histamine producing bacteria. BIOCOM has shown that control of these bacteria in chilled seafood is of major importance in reducing histamine fish poisoning. Several well known bacteria, including Morganella morganii, are able to form toxic concentrations of histamine in seafood when products are kept above 7-10°C. The BIOCOM project has confirmed the importance of these bacteria with respect to histamine formation in seafood stored at high temperature. Chilling seafood to 2-5°C eliminates histamine formation by the mesophilic bacteria. However, psychrotolerant bacteria can produce toxic concentrations of histamine in seafood at 2-5°C. In order to control histamine formation in chilled seafood, storage conditions as well as product characteristics and shelf-life must be carefully selected, as documented by the BIOCOM project.

: A proud Ph.D. student, Jette Emborg, in front of her award winning poster