コース: Food poisoning by histamine-producing bacteria

Marine products are a valuable source of protein, but if not handled properly, they can cause food poisoning. In order to end hunger and bring health to all people, we need to ensure that people around the world have access to safe marine products. Through our research on histamine food poisoning, we hope to improve the safety of marine products and contribute to SDGs (2 ZERO HUNGER and 3 GOOD HEALTH AND WELL-BEING).

Histamine-producing bacteria are the bacteria involved in histamine food poisoning. When histamine accumulates in large amounts in food, there is a risk of histamine food poisoning. By studying histamine-producing bacteria and control methods for them, we aim to propose safer processing and preservation methods for marine products.

Histamine food poisoning is caused by ingestion of large amounts of histamine accumulated in food. Histamine is produced from histidine by histidine decarboxylase in histamine-producing bacteria. Therefore, histamine food poisoning is common in red meat fish (tuna, bonito, mackerel, sardine, saury, etc.) with high free histidine content. Symptoms of histamine food poisoning are allergy-like symptoms such as urticaria and nausea, and it has been called allergy-like food poisoning in Japan. Since histamine is heat-stable, once histamine accumulates, food poisoning may occur even in foods that have been cooked.

　The main histamine-producing bacteria involved in histamine food poisoning of fish meat include several species of bacteria, such as Morganella morganii, M. psychrotolerans, Photobacterium phosphoreum, and P. damselae. In particular, M. psychrotolerans and P. phosphoreum are important histamine-producing bacteria because they can grow and produce histamine even at low temperatures such as 4°C. We used the MPN-PCR method, which is a combination of the most probable number (MPN) method and polymerase chain reaction (PCR), to study M. psychrotolerans, which contaminates marine products. As a result, it was confirmed that M. psychrotolerans contaminates marine products distributed in Japan, and it was also found that M. psychrotolerans isolated from these products produces high concentrations of histamine at 4°C (Kato et al., 2017). We also found that the expression of the histidine decarboxylase gene of M. psychrotolerans increases under acidic conditions, and histidine decarboxylase extracted from the bacterial cell produces histamine under various pH and temperature conditions (Wang et al., 2020a). These results reaffirm the importance of hygienic handling of marine products, including low temperature control, to prevent histamine food poisoning.

(Left) TEM observation of histamine-producing bacterium (Photobacterium sp.)
(Right) Histamine production in the culture medium (Purple discoloration around the colony due to histamine production)

In addition to low temperature control, if we can decrease histamine-producing bacteria in marine products, the safety of marine products will be enhanced. Therefore, in our laboratory, we are also studying the control of histamine-producing bacteria using disinfectant (Wang et al., 2020b) and bacteriophages (viruses that infect bacteria) (Yamaki et al., 2015; Yamaki et al., 2020).

Food poisoning by histamine-producing bacteria