WBR0298

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Dermatology, SubCategory::Infectious Disease
Prompt	[[Prompt::A 15-year old female with insulin dependent diabetes mellitus was admitted to the hospital for complaints of fever, ulcer on the nail bed of the left index finger and discharge. Her diabetes is said to be moderately controlled. She had been chronically biting her fingernails and fingertips and 5 days prior to presentation, the fingertip became tender, swollen and erythematous. It later developed pus and decreased range of movement. Physical examination revealed a low-grade fever of 38.8C. Laboratory findings include HbA1c level of 8.6% and a gram stain after a wide excision and drainage of the pus revealed gram-negative rods that corrodes agar with a bleach-like odor. Which of the following is the likely causative organism?]]
Answer A	AnswerA::Eikenella corrodens
Answer A Explanation	AnswerAExp::Correct. See explanation
Answer B	AnswerB::Capnocytophaga canimorsus
Answer B Explanation	AnswerBExp::Incorrect. Capnocytophega canimorsus is a fastidious, slow-growing Gram-negative rod that is transmitted from dog bite wounds. It typically causes cellulitis.
Answer C	AnswerC::Bartonella henselae
Answer C Explanation	[[AnswerCExp::Incorrect. Bartonella henselae is a gram negative rod or bacilli with a polar flagellum causing cat scratch disease and bacillary angiomatosis in immunocompromised patients and infection is typically transmitted from cats and dog bites, scratches, fleas]]
Answer D	AnswerD::Pasteurella multocida
Answer D Explanation	AnswerDExp::Incorrect. Pasteurella multocida is a Gram-negative, nonmotile, penicillin-sensitive coccobacillus causing cellulitis and osteomyelitis from animal bites particularly cat and dog bites
Answer E	AnswerE::Kingella kingae
Answer E Explanation	[[AnswerEExp::Incorrect. Kingella kingae is a fastidious gram-negative aerobic coccobacilli. It is best known as a cause of septic arthritis, osteomyelitis, spondylodiscitis, bacteraemia, and endocarditis, and less frequently lower respiratory tract infections and meningitis]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The causative organism of these symptoms in this patient is Eikenella corrodens. Eikenella corrodens is a fastidious gram-negative facultative anaerobic bacillus. It corrodes agar with a bleach-like odor. E. corrodens is a commensal of the human mouth and upper respiratory tract. It is an unusual cause of infection and when it is cultured, it is most usually found mixed with other organisms. Infections most commonly occur in patients with cancers of the head and neck, but it is also the common in human bite infections, especially "reverse bite" or "fight bite", or "clenched fist injuries". It also causes infections in insulin-dependent diabetics and intravenous drug users who lick their needles. It is one of the HACEK group of infections which are a cause of culture-negative endocarditis. E. corrodens infections are typically indolent (the infection does not become clinically evident until a week or more after the injury). They also mimic anaerobic infection in being extremely foul-smelling. HACEK group: Hemophilus influenza, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae Educational Objective Eikenella corrodens, a gram-negative rod that corrodes agar with a bleach-like odor causes human bite infections seen in insulin dependent diabetes mellitus References: First AID for the USMLE step 1 Pg 154 Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Gram-negative rod corroding agar; human bite
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