WBR292

Author	PageAuthor::Gerald
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Gastrointestinal
Prompt	[[Prompt::A 26-year-old male presents to the clinic with abdominal cramps, general malaise, fever, and profound diarrhea 3 hours after a potluck dinner. Three of his family members also have similar symptoms. Stool samples show numerous polymorphonuclear leukocytes and are positive for growth on a selective medium under CO2 incubation at 42°C. The causal agent is also found to possess an enzyme that catalyzes the transport of electrons from NADPH to oxygen. Which of the following descriptions best explains the pathogenesis of the diarrheal ailment?]]
Answer A	AnswerA::ADP-ribosylation of the Gs alpha subunit proteins using nicotinamide adenine dinucleotide (NAD).
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) thus inhibiting protein synthesis.
Answer B Explanation	AnswerBExp::Exotoxin A from Pseudomonas aeruginosa involves ADP-ribosylation of elongation factor 2 (EF-2).
Answer C	AnswerC::Invasion of colonic mucosa with disruption of epithelial cells.
Answer C Explanation	AnswerCExp::Campylobacter jejuni infection involves invasion of colonic mucosa with disruption of epithelial cells.
Answer D	AnswerD::Activation of guanylyl cyclase that enhances intestinal secretion.
Answer D Explanation	AnswerDExp::Heat-stable toxin (STa) of ETEC involves activation of guanylyl cyclase that enhances intestinal secretion.
Answer E	AnswerE::Preformed toxin that act on central autonomous nervous system.
Answer E Explanation	AnswerEExp::Staphylococcus aureus, Bacillus cereus, and Clostridium botulinum produce preformed toxins in ingested food.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Campylobacter jejuni is a curved, helical-shaped, non-spore forming, Gram-negative, microaerophilic bacteria. It is one of the most common causes of human gastroenteritis in the world. It has been linked with subsequent development of Guillain-Barré syndrome, which usually develops two to three weeks after the initial illness. C. jejuni is commonly associated with poultry, and it naturally colonizes the digestive tract of many bird species. Campylobacter is grown on specially selective agar plates at 42°C, the normal avian body temperature, rather than at 37°C, the temperature at which most other pathogenic bacteria are grown. Since the colonies are oxidase positive, they will usually only grow in scanty amounts on the plates. Microaerophilic conditions are required for luxurious growth. A selective blood agar medium (Skirrow's medium) can be used. Greater selectivity can be gained with an infusion of a cocktail of antibiotics: vancomycin, polymixin-B, trimethoprim and actidione. Important oxidase-positive pathogens: Campylobacter Helicobacter Legionella Neisseria Pseudomonas Vibrio Educational Objective: Campylobacter jejuni grows at 42°C and causes intestinal disease by invasion of the colonic mucosa. References: First Aid 2014 page 140]]
Approved	Approved::Yes
Keyword	WBRKeyword::Campylobacter jejuni, WBRKeyword::Bacteria, WBRKeyword::Gram negative, WBRKeyword::Gastroenteritis, WBRKeyword::Microbiology, WBRKeyword::Toxin
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