Effects of environmental factors on histamine production in the psychrophilic histamine-producing bacterium Photobacterium iliopiscarium

• Photobacterium iliopiscarium was shown to produce histamine under pH 5.0–pH 7.
• The amount of histamine produced increased with the decreasing pH.
• This trend was seen at all the investigated temperatures; 5 °C, 10 °C, and 20 °C.
• The risk of food poisoning was shown to be particularly high in low-pH food products.

Outbreaks of histamine-related food poisoning are mainly caused when histidine-rich red fish are not preserved at an optimal temperature, which triggers the bacterial production of histamines. However, it has been found that food poisoning occurs even when the temperature is managed by refrigeration, thus drawing our attention to the histamine-producing bacteria, which can proliferate at lower temperatures. In the present study, we investigated the effects of environmental factors (temperature and pH) on the histamine production of the psychrophilic bacterial species, Photobacterium iliopiscarium. The results of culturing this bacterium in a histidine broth suggested that there was a risk of histamine food poisoning at all of the investigated culturing temperatures (5 °C, 10 °C, and 20 °C). The amount of histamine produced exceeded 500 ppm after a certain period, and high levels of histamine were produced at low pH. Moreover, this trend was also seen in the level of expression of the hdcA gene. The present study suggests that the risk of bacterial food poisoning is particularly high in low-pH food products.