A new type of histamine-forming bacteria - III. Seasonal variations in numbers of psychrophilic and halophilic histamine-forming bacteria (N-group bacteria) in seawater and on marine fishes.

Abstract

In the previous papers, the authors repored that a new type of histamine-forming bacteria (tentatively named N-group bacteria) was isolated from a common a mackerel, and that this group of bacteria were also found in Pacific saury and sardine, and gew well at 2.5 storage of thee fish samples. The present study was undertaken to obtain more information as to seasonal variation in the mumber of N-group bacteria in seawater and on the fisher skins and intesines. N-group bacteria werre found most abundantly in the sewater during the late autumn and winter, and it is considered that this group of bacteria strikingly decreased in number when the water temperature rose above 22°C. The majouity of the fresh fish samples had less than 100 organisms of organisms of N-group bacteria per cm2 of skin; and especially in the summer samples, they were below 10 orgainisms. The number of this group of bacteria increased at 2.5storage of the fish samples and eached to 107-108 level in a few samples. This group of bacteria were found in all of the intesine amples, where their number ranged from 103 to 108 per gram. A selective enrichment medium with PH 4.5 was devised for detection and isolation of N-group bacteria.