Distribution on Fishery Products and Histamine Producing Ability of Morganella psychrotolerans , a Psychrotrophic Histamine-Producing Bacterium

Morganella psychrotolerans is a novel psychrotrophic histamine producing bacterium and seems to cause histamine fish poisoning (scombroid poisoning). However, there is little information about the occurrence and histamine producing ability of this bacterium for food contamination. To elucidate the contamination status of M. psychrotolerans, we used an MPN-PCR method that can determine bacterial number more sensitive than a traditional plating method. Many kinds of fish samples purchased in Hokkaido and water samples collected in Hakodate area were used in this study. Eighty-five MPN-PCR positive samples were found in total 192 samples (44.3%) and thirty-seven strains of M. psychrotolerans were isolated from the positive samples. It suggests M. psychrotolerans is widely distributed in retail seafood product in Japan. Then the amounts of histamine produced by M. psychrotolerans isolates were investigated. All isolates produced more than 4,000 mg/L (4,000 ppm) of histamine after 48 h incubation at 25°C. Next, the growth and histamine production of M. psychrotolerans (JCM 16473T, strain Mps. 3 from a horse mackerel sample) and Photobacterium phosphoreum NBRC 103031T was compared in the liquid media containing 0.1 or 2.0% NaCl at 4°C. At 0.1% NaCl, histamine concentration produced by M. psychrotolerans was higher than that by P. phosphoreum. It indicates M. psychrotolerans will also become one of the important bacteria associated with histamine-poisoning at refrigeration temperature on seafood, as well as P. phosphoreum.