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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Infectious Disease
|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?
|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?
|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.
|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.
|AnswerA=Actinomyces israelii
|AnswerA=Actinomyces israelii
|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.
|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.
|AnswerB=Listeria monocytogenes
|AnswerB=Listeria monocytogenes
|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.
|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.
|AnswerC=Nocardia asteroides
|AnswerC=Nocardia asteroides
|AnswerCExp=Nocardia asteroides is a gram-positive rod and weakly acid-fast aerobe in soil. It causes pulmonary infections in immunocompromised patients.
|AnswerCExp=[[Nocardia asteroides]] is a gram-positive rod and weakly acid-fast aerobe found in soil. It causes pulmonary infections in immunocompromised patients.
|AnswerD=Salmonella typhi
|AnswerD=Salmonella typhi
|AnswerDExp=Salmonella typhi is a gram-negative rod that causes typhoid fever.
|AnswerDExp=[[Salmonella typhi]] is a gram-negative rod that causes [[typhoid fever]].
|AnswerE=Shigella
|AnswerE=Shigella
|AnswerEExp=Shigella is a gram-negative non-motile rod causing enterocolitis/shigellosis, a most severe form of dysentery.
|AnswerEExp=[[Shigella]] is a gram-negative non-motile rod causing enterocolitis/shigellosis, severe form of dysentery.
|EducationalObjectives=Listeria monocytogenes is a gram-positive rod with "tumbling" motility on light microscopy.
|References=First Aid 2014 page 133
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=Microbiology, Listeria, Listeria monocytogenes, Bacteria, Abdominal pain, Diarrhea, Infection, Food poisoning
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 01:34, 21 March 2014
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.
References: First Aid 2014 page 133]]

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::
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