SHIGELLA ENTEROTOXIN-1 - AN ENTEROTOXIN OF SHIGELLA-FLEXNERI 2A ACTIVE IN RABBIT SMALL-INTESTINE IN-VIVO AND IN-VITRO

Culture filtrates of Shigella flexneri 2a strain M4243 grown in iron-d epleted medium, caused significant fluid accumulation in rabbit ileal loops, Also, when tested in Ussing chambers, a greater rise in potenti al difference and short circuit current was seen with such filtrates c ompared with the medium control, Analogous filtrates from two M4243 de rivatives lacking the 140-MD invasiveness plasmid (either M4243avir or BS103) retained 60-65% of the wild-type enterotoxic activity, Ultrafi ltration and gel exclusion size fractionation of M4243 filtrate reveal ed that the activity was similar to 60 kD, SDS-PAGE performed on this fraction showed 18 bands, 5 of which reacted with human convalescent s era, Genes encoding this enterotoxin, named ShET1 for Shigella enterot oxin I, were cloned from the S, flexneri 2a chromosome, and two separa te open reading frames of 534 and 186 bp were sequenced, These observa tions suggest that S, flexneri 2a elaborates two distinct enterotoxins : ShET1, encoded by genes located on the chromosome, and ShET2, encode d by a gene on the 140-MD invasiveness plasmid, ShET1, which is compos ed of two distinct subunits and is elaborated in vivo, where it elicit s an immune response, may be important in the pathogenesis of diarrhea l illness due to S, flexneri 2a.