WBR293: Difference between revisions
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{{WBRQuestion | {{WBRQuestion | ||
|QuestionAuthor=Gerald | |QuestionAuthor=Gerald Chi (Reviewed by {{YD}}) | ||
|ExamType=USMLE Step 1 | |ExamType=USMLE Step 1 | ||
|MainCategory=Microbiology | |MainCategory=Microbiology | ||
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|MainCategory=Microbiology | |MainCategory=Microbiology | ||
|SubCategory=Gastrointestinal | |SubCategory=Gastrointestinal | ||
|MainCategory=Microbiology | |||
|MainCategory=Microbiology | |MainCategory=Microbiology | ||
|MainCategory=Microbiology | |MainCategory=Microbiology | ||
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|MainCategory=Microbiology | |MainCategory=Microbiology | ||
|SubCategory=Gastrointestinal | |SubCategory=Gastrointestinal | ||
|Prompt=A 27-year-old | |Prompt=A 27-year-old man presents to the clinic with abdominal cramps, general malaise, fever, and diarrhea 5 hours after consuming hamburgers. He has dry mucosa and decreased skin turgor. Few leukocytes are found in his fecal specimen. Growth of colorless colonies on sorbitol-MacConkey agar is noted. Which of the following descriptions best explains the pathogenesis of the organism responsible for this patient's condition? | ||
|Explanation=''Escherichia coli'' O157:H7 (EHEC) is an enterohemorrhagic strain of ''Escherichia coli''. Infection may lead to hemorrhagic diarrhea and subsequent development of hemolytic-uremic syndrome (HUS). Transmission is via the fecal-oral route, and the majority of cases are associated with ingestion of undercooked, contaminated ground beef or pork. | |||
|Explanation=Escherichia coli O157:H7 is an enterohemorrhagic strain of Escherichia coli. Infection may lead to hemorrhagic diarrhea and | |||
''E. coli'' O157:H7 is negative for invasiveness (Sereny test), adheres through the E. coli common pilus (ECP), and does not produce heat-stable or heat-labile toxins. In addition, ''E. coli'' O157:H7 is usually sorbitol negative, whereas other ''E. coli'' ferment sorbitol. ''E. coli'' O157:H7 also lacks the ability to hydrolyze 4-methylumbelliferyl-β-D-glucuronide (MUG) and does not grow at 45 °C in the presence of 0.15% bile salts (cannot be isolated by using standard fecal coliform methods that include incubation at 45 °C). | |||
Among the virulence factors are periplasmic catalase and shiga-like toxins. Shiga-like toxin (SLT-1) is an iron-regulated toxin that catalytically inactivates 60S ribosomal subunits of eukaryotic cells. It cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. | |||
|AnswerA=ADP-ribosylation of the Gs alpha subunit proteins | |||
|AnswerAExp=Cholera toxin involves ADP-ribosylation of the Gs alpha subunit proteins. | |AnswerAExp=Cholera toxin involves ADP-ribosylation of the Gs alpha subunit proteins. | ||
|AnswerB=ADP-ribosylation of elongation factor 2 (EF-2) | |||
|AnswerB=ADP-ribosylation of elongation factor 2 (EF-2) | |||
|AnswerBExp=Exotoxin A from Pseudomonas aeruginosa involves ADP-ribosylation of elongation factor 2 (EF-2). | |AnswerBExp=Exotoxin A from Pseudomonas aeruginosa involves ADP-ribosylation of elongation factor 2 (EF-2). | ||
|AnswerC=Cleavage of N-glycoside bond of adenine in 28S ribosomal RNA | |||
|AnswerC=Cleavage of N-glycoside bond of adenine in 28S ribosomal RNA | |AnswerCExp=Shiga-like toxin-1 (SLT-1) of EHEC cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. | ||
|AnswerD=Attachment of epithelium and effacement of microvilli | |||
|AnswerCExp= | |||
|AnswerD=Attachment of epithelium and effacement of microvilli | |||
|AnswerDExp=In EPEC, attachment of epithelium and effacement of microvilli is mediated via phosphorylation of Tir and subsequent intimin binding. | |AnswerDExp=In EPEC, attachment of epithelium and effacement of microvilli is mediated via phosphorylation of Tir and subsequent intimin binding. | ||
|AnswerE=Local invasion of colonic mucosa | |||
|AnswerE=Local invasion of colonic mucosa | |||
|AnswerEExp=In EIEC, diarrhea is caused by local invasion of colonic mucosa. | |AnswerEExp=In EIEC, diarrhea is caused by local invasion of colonic mucosa. | ||
|EducationalObjectives=''Escherichia coli'' O157:H7 (EHEC) is an enterohemorrhagic strain of ''Escherichia coli''. Transmission is via the fecal-oral route, and the majority of cases are associated with ingestion of undercooked, contaminated ground beef or pork. Shiga-like toxin-1 (SLT-1) of EHEC cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. | |||
|References=First Aid 2015 page 138. | |||
|RightAnswer=C | |RightAnswer=C | ||
|WBRKeyword=Escherichia coli | |WBRKeyword=Escherichia coli, Gastroenteritis, Shiga-like toxin | ||
|Approved= | |Approved=Yes | ||
}} | }} |
Latest revision as of 03:01, 28 October 2020
Author | [[PageAuthor::Gerald Chi (Reviewed by Yazan Daaboul, M.D.)]] |
---|---|
Exam Type | ExamType::USMLE Step 1 |
Main Category | MainCategory::Microbiology |
Sub Category | SubCategory::Gastrointestinal |
Prompt | [[Prompt::A 27-year-old man presents to the clinic with abdominal cramps, general malaise, fever, and diarrhea 5 hours after consuming hamburgers. He has dry mucosa and decreased skin turgor. Few leukocytes are found in his fecal specimen. Growth of colorless colonies on sorbitol-MacConkey agar is noted. Which of the following descriptions best explains the pathogenesis of the organism responsible for this patient's condition?]] |
Answer A | AnswerA::ADP-ribosylation of the Gs alpha subunit proteins |
Answer A Explanation | AnswerAExp::Cholera toxin involves ADP-ribosylation of the Gs alpha subunit proteins. |
Answer B | AnswerB::ADP-ribosylation of elongation factor 2 (EF-2) |
Answer B Explanation | AnswerBExp::Exotoxin A from Pseudomonas aeruginosa involves ADP-ribosylation of elongation factor 2 (EF-2). |
Answer C | AnswerC::Cleavage of N-glycoside bond of adenine in 28S ribosomal RNA |
Answer C Explanation | AnswerCExp::Shiga-like toxin-1 (SLT-1) of EHEC cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. |
Answer D | AnswerD::Attachment of epithelium and effacement of microvilli |
Answer D Explanation | AnswerDExp::In EPEC, attachment of epithelium and effacement of microvilli is mediated via phosphorylation of Tir and subsequent intimin binding. |
Answer E | AnswerE::Local invasion of colonic mucosa |
Answer E Explanation | AnswerEExp::In EIEC, diarrhea is caused by local invasion of colonic mucosa. |
Right Answer | RightAnswer::C |
Explanation | [[Explanation::Escherichia coli O157:H7 (EHEC) is an enterohemorrhagic strain of Escherichia coli. Infection may lead to hemorrhagic diarrhea and subsequent development of hemolytic-uremic syndrome (HUS). Transmission is via the fecal-oral route, and the majority of cases are associated with ingestion of undercooked, contaminated ground beef or pork.
E. coli O157:H7 is negative for invasiveness (Sereny test), adheres through the E. coli common pilus (ECP), and does not produce heat-stable or heat-labile toxins. In addition, E. coli O157:H7 is usually sorbitol negative, whereas other E. coli ferment sorbitol. E. coli O157:H7 also lacks the ability to hydrolyze 4-methylumbelliferyl-β-D-glucuronide (MUG) and does not grow at 45 °C in the presence of 0.15% bile salts (cannot be isolated by using standard fecal coliform methods that include incubation at 45 °C). Among the virulence factors are periplasmic catalase and shiga-like toxins. Shiga-like toxin (SLT-1) is an iron-regulated toxin that catalytically inactivates 60S ribosomal subunits of eukaryotic cells. It cleaves N-glycoside bond of adenine in 28S rRNA of the 60S ribosome unit to prevent EF-1-dependent aminoacyl tRNA binding, thereby inhibiting protein synthesis. |
Approved | Approved::Yes |
Keyword | WBRKeyword::Escherichia coli, WBRKeyword::Gastroenteritis, WBRKeyword::Shiga-like toxin |
Linked Question | Linked:: |
Order in Linked Questions | LinkedOrder:: |