A 25-year-old woman comes to the emergency department due to 2 days of abdominal pain and bloody diarrhea. A few days ago, she attended a church barbeque party. The patient lives alone and has no medical problems. She does not know if anyone else at the party developed similar symptoms. Her temperature is 37.1 C (98.8 F), blood pressure is 119/76 mm Hg, pulse is 92/min, and respirations are 16/min. There is abdominal tenderness with no rebound or guarding. Guaiac-positive bloody stools are detected on rectal examination. Stool cultures reveal an Escherichia coli strain that does not produce glucuronidase and does not ferment sorbitol on sorbitol-containing MacConkey agar. Which of the following best describes the mechanism of action of the toxin produced by these bacteria?

Question

A 25-year-old woman comes to the emergency department due to 2 days of abdominal pain and bloody diarrhea.  A few days ago, she attended a church barbeque party.  The patient lives alone and has no medical problems.  She does not know if anyone else at the party developed similar symptoms.  Her temperature is 37.1 C (98.8 F), blood pressure is 119/76 mm Hg, pulse is 92/min, and respirations are 16/min.  There is abdominal tenderness with no rebound or guarding.  Guaiac-positive bloody stools are detected on rectal examination.  Stool cultures reveal an Escherichia coli strain that does not produce glucuronidase and does not ferment sorbitol on sorbitol-containing MacConkey agar.  Which of the following best describes the mechanism of action of the toxin produced by these bacteria?

Quizplus · Accepted Answer

11ec160b_386b_c1d1_9249_db54fcc61dc4_MD0001_00 Enterohemorrhagic Escherichia coli (EHEC) O157:H7 can cause hemorrhagic colitis, most characteristically following ingestion of inadequately cooked hamburger meat. In contrast to most E coli strains, O157:H7 E coli does not ferment sorbitol during overnight incubation. As a result, sorbitol-containing MacConkey agar is used for isolation. Also, unlike other E coli strains, E coli O157:H7 does not produce glucuronidase. EHEC elaborates a Shiga-like toxin virtually identical to the Shiga toxin produced by Shigella dysenteriae. This toxin is phage encoded, and its production is enhanced by iron deficiency. The Shiga and the Shiga-like toxins inactivate the 60s ribosomal subunit in human cells, leading to an inhibition of protein synthesis and eventual cell death. Infection with EHEC can also lead to hemolytic-uremic syndrome, characterized by thrombocytopenia, microangiopathic hemolytic anemia, and renal insufficiency (sometimes with uremia). Unlike enteroinvasive E coli, EHEC does not invade the intestinal mucosa. Unlike enterotoxigenic E coli (ETEC), EHEC does not produce heat-labile toxin (LT) or heat-stable toxin (ST). (Choice A) Toxins produced by Bordetella pertussis (adenylate cyclase toxin), ETEC (LT), Campylobacter jejuni (C jejuni enterotoxin), and Vibrio cholerae (choleragen toxin) result in increased intracellular cyclic AMP in intestinal mucosal cells, which leads to decreased absorption and increased secretion of sodium, chloride, and water. (Choice B) ETEC (ST) and Yersinia enterocolitica (Y enterocolitica enterotoxin) produce toxins that increase intracellular cyclic GMP, leading to watery diarrhea and electrolyte loss. (Choice C) Clostridium difficile produces an exotoxin capable of disrupting the cytoskeleton (toxin B/cytotoxin). This toxin acts by depolymerizing actin, leading to cell death. (Choice D) Exotoxins produced by Corynebacterium diphtheriae (diphtheria toxin) inhibit protein synthesis in eukaryotic cells by catalyzing ADP-ribosylation of elongation factor (EF)-2, causing EF-2 inactivation. Educational objective: Enterohemorrhagic Escherichia coli O157:H7 infection is a common cause of bloody diarrhea and can lead to hemolytic-uremic syndrome. It is associated with consumption of undercooked ground beef and elaborates a Shiga-like toxin capable of inhibiting protein synthesis in colonic mucosal cells and renal endothelial cells. This particular strain of E coli is unable to ferment sorbitol and does not produce a glucuronidase.

A 25-Year-Old Woman Comes to the Emergency Department Due to 2