Immunomagnetic particles Dynabeads M-280 sheep anti-rabbit immunoglobulin G (Dynabeads) coated with antibodies against the K6 antigen ofVibrio parahaemolyticuswere used for isolation of thermostable direct hemolysin-producingV. parahaemolyticusK6 serovar (TDH⁺V.pK6) from a sea water culture. Samples were collected at four major fishing ports in Toyama bay during September to November in 1998, and 1, 000ml of sample were cultured in Salt Polymyxin Broth after precultivation with Trypticase Soy Broth containing 3% NaCl. The isolation rate of the TDH⁺V.pK6 from sea water was 4/10 (40%), and the number of TDH⁺V.pK6 in sea water were 0-3.6/1, 000ml although the total number ofV. parahaemolyticuswere 2.3×10²-1.1×10⁴/1, 000ml.
Pulsed-field gel electrophoresis pattern of the TDH⁺V.pK6 strains from sea water were divided into two closely related types (provisional type: 1a, 1b). Most of TDH⁺V.pK6 isolates from food poisoning cases in Japan were also type 1a or 1b . The serotype of isolates fromV. parahaemolyticusfood poisoning that occurred in Toyama Prefecture during June to October, 1998 were 03: K6 in eight of 11 cases. These results show that food poisoning-causative TDH⁺V.pO3: K6 is distributed in sea water of fishing ports.

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The effects of temperature (10 to 45°C), initial pH (3.8 to 6.6) and NaCl (0 to 10%) in 1%Tryptone water on the growth of Salmonella Oranienburg and Salmonella Chester isolated from dried squid were determined. Growth of S. Oranienburg occurred between 13°Cand 45°C, and of S.Chester, between 13°Cand 42.5°C. At a pH<4.4, populations of both strains decreased. After 62 hrs at 10% NaCl concentration, there was no S. Chester detected while S. Oranienburg survived. The ratios of the population of S. Oranienburg and S. Chester, which were simultaneously inoculated with different ratio, did not change during the growth. Observation of Salmonella in three types (classified into three shapes of so-men, tanzaku and square) of dried squid samples kept at a temperature of 25±1°C with 55±5% humidity rerealed a similar decrease in Salmonella populations in all three types. Population growth in a so-men-shaped sample exposed to 1.6×10³ cfu/g ofSalmonellawas detected by204 days, in the tanzaku shape exposed to 1.1×10¹ cfu/g, by 70 days, and in the square shape exposed to 1.1×10⁴ cfu/g, by 245 days.The original ratio of S. Oranienburg to S. Chester was 6: 4, changing to 7: 3 after 7 days and 9: 1 after 21 days.

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A rapid assay was developed for detection of small numbers ofCampylobactercells in food samples. The intergenic sequence between the 16S rRNA gene ofCampylobacter jejuniwas amplified and characterized with a triple primer or semi-nested primer approach . The detection limit as determinated by ethidium bromide staining of amplification products on agarose gels was 10 bacteria or fewer in artificially contaminated samples with the seminested PCR assay.

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