WBR0298

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Alison Leibowitz)]]
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 presents to the hospital for complaints of a fever, ulcer on the nail bed of the left index finger, and discharge. She has been habitually biting her fingernails and fingertips, and 5 days prior to presentation, the fingertip became tender, swollen, and erythematous. The fingertip is observed to be excreting pus and the finger has a decreased range of movement. Physical examination reveals a low-grade fever of 38.8 °C. Laboratory findings include a HbA1c level of 8.6% and a Gram-staining of the pus that demonstrates Gram-negative rods, with bleach like odor, corroding the agar. Which of the following organisms is the likely the cause of the patient's symptoms?]]
Answer A	[[AnswerA::Eikenella corrodens]]
Answer A Explanation	AnswerAExp::See explanation
Answer B	AnswerB::Capnocytophaga canimorsus
Answer B Explanation	AnswerBExp::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::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::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::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 organism likely causing the patient's symptoms isEikenella corrodens. Eikenella corrodens is a fastidious, Gram-negative, facultative anaerobic bacillus, which corrodes agar with a bleach-like odor. Eikenella corrodens is a commensal of the human mouth and upper respiratory tract. Eikenella corrodens, is usually observed to be mixed with other organisms when cultured. Infections most commonly occur in patients with cancers of the head and neck, but can also occur in human bite infections, such as reverse bites or fight bites. Eikenella corrodens also can cause 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. Eikenella 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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