Escherichia coli O157:H7 produces a toxin similar to Shiga toxin produced by which organism?

• A. Staphylococcus aureus
• B. Shigella dysenteriae
• C. Clostridium difficile
• D. Vibrio cholerae

Answer: (B)

The toxin produced by Escherichia coli O157:H7 is a Shiga-like toxin, mirroring the Shiga toxin originally described in Shigella dysenteriae. Both toxins are AB5 types that bind to the Gb3 receptor on cells; the A subunit enzymatically inactivates ribosomes by depurinating a residue in 28S rRNA, stopping protein synthesis and leading to cell death. This mechanism underlies the severe intestinal injury and can progress to hemolytic uremic syndrome seen with O157:H7 infections. Staphylococcus aureus produces enterotoxins, Clostridium difficile makes toxins A and B causing colitis, and Vibrio cholerae produces cholera toxin, which raises cAMP and causes watery diarrhea—different toxins and disease patterns from Shiga-like toxins.