WBR0086

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Will Gibson, Jad Al Danaf, Rim Halaby, M.D. [2])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 38-year-old male presents to the emergency department with a 2-day history of fever, headache, generalized body weakness, mild abdominal pain, diarrhea and vomiting. He had just returned from a trip to Sweden 5 days prior to the onset of his symptoms. He reports that during his travel, he had tried raw milk for the first time in his life and loved its taste. Physical examination is unremarkable. Laboratory culture of his blood reveals a gram-positive rod with tumbling motility. Which of the following is the most likely causative organism?]]
Answer A	AnswerA::Actinomyces israelii
Answer A Explanation	[[AnswerAExp::Actinomyces israelii is a gram positive rod that forms long branching filaments resembling fungi. It causes oral/facial abscesses that drain through sinus tracts in skin.]]
Answer B	AnswerB::Listeria monocytogenes
Answer B Explanation	[[AnswerBExp::Listeria monocytogenes is a gram positive rod with a characteristic tumbling motility. Infection is typically acquired commonly through ingestion of unpasteurized milk/cheese and deli meats or by vaginal delivery.]]
Answer C	AnswerC::Nocardia asteroides
Answer C Explanation	[[AnswerCExp::Nocardia is a gram positive rod and weakly acid-fast aerobe found in soil. It causes pulmonary infections in immunocompromised patients.]]
Answer D	AnswerD::Salmonella typhi
Answer D Explanation	[[AnswerDExp::Salmonella typhi is a gram negative rod that causes typhoid fever.]]
Answer E	AnswerE::Shigella
Answer E Explanation	[[AnswerEExp::Shigella is a gram negative non-motile rod causing enterocolitis or shigellosis, a severe form of dysentery.]]
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient in this vignette is suffering from an infection caused by Listeria monocytogenes. L. monocytogenes is a facultative intracellular gram positive rod that displays a characteristic "tumbling" motility when viewed on light microscopy. It is beta hemolytic and has a blue-green sheen on blood agar. Listeriosis is relatively rare and occurs primarily in newborn infants, elderly patients, and patients who are immunocompromised. Transmission is either food-borne (unpasteurized dairy) or by vaginal transmission during birth. It can cause amnionitis, septicemia, neonatal meningitis, meningitis in immunocompromised patients, or mild gastroenteritis in healthy individuals. Educational Objective: Listeria monocytogenes is a gram positive rod with "tumbling" motility on light microscopy. In healthy adults, it usually causes mild gastrointestinal symptoms. References: First Aid 2014 page 133, CDC.gov [http://www.cdc.gov/pulsenet/pathogens/listeria.html) Listeriosis: CDC (http://www.cdc.gov/listeria/definition.html]]]
Approved	Approved::Yes
Keyword	WBRKeyword::Microbiology, WBRKeyword::Listeria, WBRKeyword::Listeria monocytogenes, WBRKeyword::Bacteria, WBRKeyword::Abdominal pain, WBRKeyword::Diarrhea, WBRKeyword::Infection, WBRKeyword::Food poisoning
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