Which organism is shiga toxin–producing and associated with bloody diarrhea?

• A. Shigella
• B. Escherichia coli STEC
• C. Salmonella
• D. Campylobacter

Answer: (B)

Shiga toxin–producing strains define a group of Escherichia coli that cause hemorrhagic colitis with bloody diarrhea and can lead to hemolytic uremic syndrome in children. The Shiga toxin inhibits protein synthesis by inactivating the 60S ribosomal subunit, damaging intestinal vascular endothelium and triggering severe inflammation and bleeding in the colon. These toxins are carried by a lysogenic bacteriophage integrated into the E. coli genome, and the typical human source is undercooked beef (ground meat) or contaminated produce. While other bacteria on the list can cause bloody diarrhea through inflammatory damage, they are not characterized by Shiga toxin production. Therefore, the organism most specifically associated with Shiga toxin production and bloody diarrhea is Shiga toxin–producing Escherichia coli.