Unique features of heat-stable enterotoxin of Shigella flexneri.

Sephadex G-100 fractions of ultrasonic lysate of Shigella felxneri were compared to the fractions of Escherichia coli lysates of Ent- , LT+ ST+, LT+ and ST+ strains. The range of molecular weight of S. flexneri ST fractions was the same as that of E. coli LT fractions. Rapid PF activity was associated with the ST peak in the case of S. flexneri, and followed the LT activity in the E. coli (LT+ ST+) fractions, and appeared in the same molecular weight range in the case of Ent- E. coli lysate. Cross neutralization could be demonstrated between S. flexneri ST and E. coli LT. Antigenic relationship between shigella ST and choleragen seemed to be less expressed and rather unilateral.