WBR0086
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]] |
|---|---|
| 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, diarrhea and vomiting. He had just returned from a trip to Africa 5 days prior to the onset of his symptoms. Physical examination is unremarkable. Laboratory culture 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 asteroides 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/shigellosis, 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. 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. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Listeria, WBRKeyword::Listeria monocytogenes, WBRKeyword::Bacteria, WBRKeyword::Abdominal pain, WBRKeyword::Diarrhea, WBRKeyword::Infection, WBRKeyword::Food poisoning |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |