WBR0086

Author	PageAuthor::Ogheneochuko Ajari MB.BS, MS
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 38-year-old male presented to the emergency department with a 2-day history of fever, headache, generalized body weakness, diarrhea and vomiting. He had just returned from a trip to Africa 5 days prior to his symptoms. Physical examination is unremarkable. Laboratory culture revealed a gram-positive rod with tumbling motility. Which of the following is the causative organism?]]
Answer A	AnswerA::Actinomyces israelii
Answer A Explanation	AnswerAExp::Actinomyces israelii is a gram-positive rod forming long branching filaments resembling fungi. It causes oral/facial abscesses that drain through the sinus tract in skin.
Answer B	AnswerB::Listeria monocytogenes
Answer B Explanation	AnswerBExp::Listeria monocytogenes is a gram-positive rod with a characteristic tumbling motility with the infection acquired commonly by the ingestion of unpasteurized milk/cheese and deli meats or by vaginal delivery.
Answer C	AnswerC::Nocardia asteroides
Answer C Explanation	AnswerCExp::Nocardia asteroides is a gram-positive rod and weakly acid-fast aerobe 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/shigellosis, a most severe form of dysentery.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The patient in this vignette is suffering from an infection caused by Listeria monocytogenes. It is a facultative intracellular gram positive-rod, non-spore forming with a characteristic tumbling motility when viewed on light microscopy. It is beta hemolytic and has a blue-green sheen on blood agar. Transmission is either foodborne (where it grows in cold environments and it could be acquired by ingestion of contaminated soft cheeses, deli meats, cabbages (coleslaw), hotdogs) or by vaginal transmission during birth. It can cause amnionitis, septicemia, neonatal meningitis, meningitis in immunocompromised patients, mild gastroenteritis in healthy individuals. Educational Objective: References: ]]
Approved	Approved::Yes
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