Distribution of psychrophilic and mesophilic histamine-producing bacteria in retailed fish in Japan

Cases of histamine fish poisoning (HFP) have been reported worldwide. Although most cases of HFP are caused by mesophilic histamine-producing bacteria (HPB) when temperature abuse occurs, HFP could also be caused by psychrophilic HPB when fish are stored at low temperatures. In this study, mesophilic and psychrophilic HPB were isolated from a wide range of fish samples and identified by 16S rRNA and gyrB sequencing. Most of the mesophilic isolates were Photobacterium damselae subsp. damselae (42.7%) and Morganella morganii (24.0%), and most of the psychrophilic HPB were Photobacterium (94.9%). Whereas 76.0% of the mesophilic HPB produced more than 500 mg/kg of histamine (Hm), psychrophilic HPB generally produced lower Hm level, but 43.2% of these isolates still produced more than 500 mg/kg Hm. This study showed the importance of investigating not only mesophilic but psychrophilic HPB as well.