WBR0298

Author	[[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [2])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 12-year-old girl with a medical history of type 1 diabetes mellitus presents to the emergency department (ED) with a painful and swollen left index finger for the past 3 days. Her mother explains that the patient habitually bites her fingernails and fingertips, and she often causes the fingertips to bleed. In the ED, the patient's temperature is 36.8 °C (98.24 °F), blood pressure is 122/78 mmHg, and heart rate is 78/min. On physical examination, the left index finger is edematous and tender to touch; it has an ulcerated lesion with a foul-smelling pus discharge under the nail bed. Lab tests are remarkable for an HbA1c of 8.6%, elevated ESR, and a WBC count within normal range. Two days later, cultures of the fingertip pus grow gram-negative rods that have a bleach-like odor and appear to corrode the surface of the agar medium. Which of the following organisms is responsible for this patient's infection?]]
Answer A	AnswerA::''Eikenella sp.''
Answer A Explanation	[[AnswerAExp::Eikenella corrodens may infect immunocompromised pediatric patients who have been exposed to human oral secretions. E. corrodens is a slow-growing, non-mobile, facultative, gram-negative bacillus that grow on blood agar in 5% carbon dioxide and has a bleach-like odor. It is unique in the way the bacteria appears to corrode the surface of the agar medium, demonstrating agar pitting and greenish discolorations that surround the colonies.]]
Answer B	AnswerB::''Capnocytophaga sp.''
Answer B Explanation	[[AnswerBExp::Capnocytophega canimorsus is a fastidious, slow-growing, gram-negative rod that is often transmitted by dog bites. It typically causes cellulitis.]]
Answer C	AnswerC::''Bartonella sp.''
Answer C Explanation	[[AnswerCExp::Bartonella henselae is a gram-negative rod with a polar flagellum. It can cause cat scratch disease and bacillary angiomatosis in immunocompromised patients. Bartonella henselae is typically transmitted by cat and dog bites, scratches, and fleas.]]
Answer D	AnswerD::''Pasteurella sp''
Answer D Explanation	[[AnswerDExp::Pasteurella multocida is a non-motile, gram-negative coccobacillus that may cause cellulitis and osteomyelitis following exposure to animal bites (cat or dog bite). Pasteurella multocida is penicillin-sensitive.]]
Answer E	AnswerE::''Kingella sp.''
Answer E Explanation	[[AnswerEExp::Kingella kingae is a fastidious, aerobic, gram-negative coccobacilli that may cause septic arthritis, osteomyelitis, spondylodiscitis, bacteremia, endocarditis, and less frequently, lower respiratory tract infections and meningitis.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::Eikenella corrodens is an opportunistic pathogen that commonly infects the adult population. However, cases of pediatric infections with E. corrodens are described among patient with a history of immunocompromised states (malignancies or uncontrolled insulin-dependent diabetes mellitus), trauma, head and neck infections, or visceral disease. E. corrodens is a slow-growing, non-mobile, facultative, gram-negative bacillus that grows on blood agar in 5% carbon dioxide. It has a unique bleach-like odor and typically appears to corrode the surface of the agar medium, demonstrating agar pitting and greenish discolorations that surround the bacterial colonies. E. corrodens normally colonizes the human oral cavity, the GI tract, and the genital tract. It is associated with the development of sinusitis, pulmonary disease, arthritis, endocarditis, abdominal infections, bone infections, and infections following human bite wounds. Similar to the patient in the vignette, children may be at high risk of E. corrodens infection when immunocompromised (uncontrolled type 1 diabetes mellitus) and are exposed to human oral secretions (habitual fingertip biting). Children who are infected with E. corrodens may present with symptoms of local acute inflammation. In patients with no E. corrodens sepsis, physical examination may include normal vital signs and findings that are typically similar to that of the patient in the vignette: local edema, erythema, tenderness, ulceration, pus formation, and foul-smelling discharge. Patients classically have no elevations in WBC count but often demonstrate increase in ESR, a biomarker of inflammation. E. corrodens is usually treated with any of penicillin G, ceftriaxone, amoxicillin, clavulonic-acid, TMP-SMX, or fluoroquinolones. Educational Objective: Eikenella corrodens may infect immunocompromised pediatric patients who have been exposed to human oral secretions. E. corrodens is a slow-growing, non-mobile, facultative, gram-negative bacillus that grow on blood agar in 5% carbon dioxide and has a bleach-like odor. It is unique in the way the bacteria appears to corrode the surface of the agar medium, demonstrating agar pitting and greenish discolorations that surround the bacterial colonies. References: Paul K, Patel SS. Eikenella corrodens infections in children and adolescents: case reports and review of the literature. Clin Infect Dis. 2001;33(1):54-61. First Aid 2014 page 142]]
Approved	Approved::Yes
Keyword	WBRKeyword::Gram-negative, WBRKeyword::Bite, WBRKeyword::Bacteria, WBRKeyword::Microbiology, WBRKeyword::Eikenella corrodens, WBRKeyword::Rod, WBRKeyword::Gram negative, WBRKeyword::Gram negative rod, WBRKeyword::Human bite, WBRKeyword::Agar, WBRKeyword::Bleach-like odor, WBRKeyword::Human oral secretions, WBRKeyword::Fingertip, WBRKeyword::Fingernails, WBRKeyword::Diabetes mellitus, WBRKeyword::Eikenella sp.
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