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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Ochuko}}
|QuestionAuthor= {{Ochuko}} (Reviewed by Will Gibson, [[user: Jad Al Danaf|Jad Al Danaf]],  {{Rim}}, and Yazan Daaboul)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Head and Neck, Infectious Disease
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|MainCategory=Microbiology
|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?
|SubCategory=Head and Neck, Infectious Disease
|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.
|Prompt=A 38-year-old healthy man presents to the emergency department (ED) for  fever, abdominal pain, vomiting, and watery diarrhea. He states that his symptoms have been present for the past 2 days and are progressively worsening. He recently returned from a trip to South America. He reports that during his travel, he ingested unpasteurized milk. Physical examination in the ED is unremarkable. Following appropriate management, the patient is prescribed antibiotics and is then discharged home. Two days later, his stool cultures reveal a gram-positive rod with tumbling motility. Which of the following organisms is most likely responsible for the patient's condition?
|AnswerA=Actinomyces israelii
|Explanation=''[[Listeria monocytogenes]]'' is a ubiquitious gram-positive facultatively-intracellular glucose-fermenting motile pathogen that causes [[listeriosis]]. It is a foodborne pathogen that is often found in dairy products, meat, fruits, and vegetables, and is also transmitted by cattle. It infects refrigerated foods due to its unusual ability to slowly grow at low temperatures: -18 °C to 10 °C.  This characteristic feature also makes the organism difficult to grow on regular cultures using usual incubation temperatures. Generally, it grows on blood agar, showing a narrow band of beta-hemolysis. ''L. monocytogenes'' induces its own uptake into non-phagocytic cells. It has the capacity to migrate in a "tumbling motility" fashion via a unique actin-polymerization process (rocket tails). Primarily, ''L. monocytogenes'' first enters the host through the intestine and directly affects the liver before involving other organs. It grows in the cytosol of infected cells and escapes phagocytosis by secretion of cholesterol-dependent cytolysin listeriolysin O (LLO).
|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.
 
|AnswerB=Listeria monocytogenes
Manifestations of listeriosis may not be directly observed following infection. Many patients remain asymptomatic for prolonged period of time. ''L. monocytogenes'' may cause meningitis or granulomatosis infantiseptica in newborns and the elderly. It may also be responsible for septicemia in adults, especially among patients with immunocompromised states, such as patients on immunosuppression (eg transplant recipients) or patients with hematologic malignancies (eg. leukemia) or receiving antineoplastic therapy. Pregnant women are also especially susceptible to ''L. monocytogenes'', who may suffer from amnionitis or spontaneous abortions. Even patients with other diseases, such as reduced gastric acidity, cirrhosis, hemochromatosis, and chronic renal failure, are at higher risk of L. monocytogenes infection. Otherwise, healthy children and adults rarely suffer from listeriosis. Manifestations may range from an asymptomatic course or febrile gastroenteritis to meningoencephalitis.
|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.
|AnswerA=''Actinomyces israelii''
|AnswerC=Nocardia asteroides
|AnswerAExp=''[[Actinomyces israelii]]'' is a [[gram-positive]] anaerobic rod that forms long branching filaments resembling [[fungi]]. It characteristically crosses tissue planes and causes oral/facial [[abscesses]] that drain through sinus tracts in skin.
|AnswerCExp=Nocardia asteroides is a gram-positive rod and weakly acid-fast aerobe in soil. It causes pulmonary infections in immunocompromised patients.
|AnswerB=''Listeria monocytogenes''
|AnswerD=Salmonella typhi
|AnswerBExp=''[[Listeria monocytogenes]]'' is a [[gram-positive]] rod with a characteristic tumbling motility. Infection is typically acquired commonly through ingestion of unpasteurized milk/cheese, poorly prepared meats.
|AnswerDExp=Salmonella typhi is a gram-negative rod that causes typhoid fever.
|AnswerC=''Nocardia asteroides''
|AnswerE=Shigella
|AnswerCExp=''[[Nocardia|Nocardia asteroides]]'' is a [[gram-positive]] rod and weakly acid-fast aerobe found in soil. It causes a clinical presentation similar to that of tuberculosis: Subacute pulmonary infections in immunocompromised patients.
|AnswerEExp=Shigella is a gram-negative non-motile rod causing enterocolitis/shigellosis, a most severe form of dysentery.
|AnswerD=''Trichomonas spp.''
|AnswerDExp=Trichomoniasis is a sexually transmitted infection caused by ''Trichomonas vaginalis''. It is an anaerobic, flagellated parasite that has a characteristic "cork-screw" motility.
|AnswerE=''Shigella spp.''
|AnswerEExp=[[Shigella]] is a [[gram-negative]], non-motile rod causing [[enterocolitis]] or [[shigellosis]], a severe form of dysentery.
|EducationalObjectives=''[[Listeria monocytogenes]]'' is a [[gram-positive]] rod with "tumbling" motility on light microscopy. In healthy adults, it usually causes symptoms of febrile gastroenteritis.
|References=Ramaswamy V, Sresence VM, Rejitha JS, et al. ''Listeria'' - review of epidemiology and pathogenesis. J Microbiol Immunol Infect. 2007;40:4-13.
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
}}
}}

Latest revision as of 23:17, 27 October 2020

 
Author [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Will Gibson, Jad Al Danaf, Rim Halaby, M.D. [2], and Yazan Daaboul)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::Head and Neck, SubCategory::Infectious Disease
Prompt [[Prompt::A 38-year-old healthy man presents to the emergency department (ED) for fever, abdominal pain, vomiting, and watery diarrhea. He states that his symptoms have been present for the past 2 days and are progressively worsening. He recently returned from a trip to South America. He reports that during his travel, he ingested unpasteurized milk. Physical examination in the ED is unremarkable. Following appropriate management, the patient is prescribed antibiotics and is then discharged home. Two days later, his stool cultures reveal a gram-positive rod with tumbling motility. Which of the following organisms is most likely responsible for the patient's condition?]]
Answer A AnswerA::''Actinomyces israelii''
Answer A Explanation [[AnswerAExp::Actinomyces israelii is a gram-positive anaerobic rod that forms long branching filaments resembling fungi. It characteristically crosses tissue planes and 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, poorly prepared meats.]]
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 a clinical presentation similar to that of tuberculosis: Subacute pulmonary infections in immunocompromised patients.]]
Answer D AnswerD::''Trichomonas spp.''
Answer D Explanation AnswerDExp::Trichomoniasis is a sexually transmitted infection caused by ''Trichomonas vaginalis''. It is an anaerobic, flagellated parasite that has a characteristic "cork-screw" motility.
Answer E AnswerE::''Shigella spp.''
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::Listeria monocytogenes is a ubiquitious gram-positive facultatively-intracellular glucose-fermenting motile pathogen that causes listeriosis. It is a foodborne pathogen that is often found in dairy products, meat, fruits, and vegetables, and is also transmitted by cattle. It infects refrigerated foods due to its unusual ability to slowly grow at low temperatures: -18 °C to 10 °C. This characteristic feature also makes the organism difficult to grow on regular cultures using usual incubation temperatures. Generally, it grows on blood agar, showing a narrow band of beta-hemolysis. L. monocytogenes induces its own uptake into non-phagocytic cells. It has the capacity to migrate in a "tumbling motility" fashion via a unique actin-polymerization process (rocket tails). Primarily, L. monocytogenes first enters the host through the intestine and directly affects the liver before involving other organs. It grows in the cytosol of infected cells and escapes phagocytosis by secretion of cholesterol-dependent cytolysin listeriolysin O (LLO).

Manifestations of listeriosis may not be directly observed following infection. Many patients remain asymptomatic for prolonged period of time. L. monocytogenes may cause meningitis or granulomatosis infantiseptica in newborns and the elderly. It may also be responsible for septicemia in adults, especially among patients with immunocompromised states, such as patients on immunosuppression (eg transplant recipients) or patients with hematologic malignancies (eg. leukemia) or receiving antineoplastic therapy. Pregnant women are also especially susceptible to L. monocytogenes, who may suffer from amnionitis or spontaneous abortions. Even patients with other diseases, such as reduced gastric acidity, cirrhosis, hemochromatosis, and chronic renal failure, are at higher risk of L. monocytogenes infection. Otherwise, healthy children and adults rarely suffer from listeriosis. Manifestations may range from an asymptomatic course or febrile gastroenteritis to meningoencephalitis.
Educational Objective: Listeria monocytogenes is a gram-positive rod with "tumbling" motility on light microscopy. In healthy adults, it usually causes symptoms of febrile gastroenteritis.
References: Ramaswamy V, Sresence VM, Rejitha JS, et al. Listeria - review of epidemiology and pathogenesis. J Microbiol Immunol Infect. 2007;40:4-13. 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
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