TABLE 1.

Serotype O157:H7 strains used in this study

Strain	Origin	Place of isolation
2	Salmon roe	Hokkaido, Japan
3	Salmon roe	Hokkaido, Japan
4	Salmon roe	Hokkaido, Japan
5	Patient	Kanagawa, Japan
6	Patient	Tokyo, Japan
7	Patient	Toyama, Japan
8	Patient	Chiba, Japan

^aToxin typing was performed by PCR and reverse passive latex agglutination (VTEC-RPLA “SEIKEN”; Denka Seiken Co., Ltd., Tokyo, Japan) as described previously (2). The toxin types of all strains were Shiga toxins 1 and 2.