Vibrio parahaemolyticus, a causative organism of food poisoning in Japan, is known to be widely distributed in the coastal sea areas, and it is supposed that fish and shellfish may be previously contaminated with the organism in sea water before landing. In the present study the authors investigated the multiplication of the organism on the flesh samples of various kinds of fish and shellfish according to the following procedures.
The sample of about 10g flesh placed in a 300ml conical beaker was inoculated with a small amount of the cells, approximately 10³, and was kept in an incubator at 33°C. After being incubated for a certain period, the cells developed on the sample were suspended in a certain amount of diluent, 3% NaCl water supplemented with 0.1% peptone, by means of a homogenizer or a shaking method, and the determination of the number of the organism was made using “a modified TCBS medium”, which was diviced for the selective colony counting of biotypes 1, 2 and 3 of Vibrio parahaemolyticus according to SAHEKI et al.¹⁾.
Results were summarized as follows:
There was no multiplication of the organism in the case of red muscled fish such as tuna, skipjack or mackerel etc., in which pH of the flesh was generally below 6.0, whereas remarkable multiplications of the organism were observed in so-called white muscled fish, fresh water fish, shellfish, squid or octopus, pH of the flesh was above 6.0. The population de-veloped in 7 hours incubation amounted to 10⁷to 10⁸. Therefore, the occurrence of the bacterial growth depends upon the pH value of the flesh.

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