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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor=Gerald Chi
|QuestionAuthor=Gerald Chi (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
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|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|SubCategory=Dermatology
|SubCategory=Dermatology
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
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|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|SubCategory=Dermatology
|SubCategory=Dermatology
|Prompt=A 55-year-old male comes to the clinic after being bitten by his wife. On examination, there is a 3-inch-long, deep puncture wound on his arm that is lined by human teeth marks. Cultures obtained at surgical debridement reveals growth of a fastidious, gram-negative facultative anaerobic bacillus. If antibiotic therapy is indicated, which of the following drugs should be used in this case?
|Prompt=A 55-year-old man presents to the emergency department after being bitten by his brother during a domestic dispute. On physical examination, the physician notices a 3 by 3 inch wound on his arm lined by human teeth marks. What is the most appropriate agent to prevent infection of the wound in this case?
|Explanation=E. corrodens is a pleomorphic bacillus that sometimes appears coccobacillary and typically creates a depression in the agar on which it is growing. It grows in aerobic and anaerobic conditions, but requires an atmosphere enhanced by 3–10% carbon dioxide. 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 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 ("needle-licker's osteomyelitis"). 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.
|Explanation=Human bite wounds can be divided into 2 different types: occlusive injuries, defined as a wound from a direct bite, or clenched-fist injuries, defined as a wound from a fist striking teeth. Bacteria associated with human bite injuries are usually part of the oral flora and include viridans streptococci, staphylococci, anaerobic organisms (Fusobacterium nucleatum, Prevotella, peptostreptococci), and Eikenella corrodens. E. corrodens is a facultatively anaerobic, pleomorphic bacillus that requires ample carbon dioxide concentrations to thrive. E. corrodens is part of the normal flora of the oral cavity and the upper respiratory tract. E. corrodens infections are common in untreated human bite wounds, especially clenched fist injuries. E. corrodens infections typically progress slowly and can manifest clinically one to two weeks after inoculation. Complications include osteomyelitis, loss of joint function, and bacteremia with endocarditis. General treatment of human bite wounds includes irrigation and topical wound cleansing, however, unlike animal bites, prophylactic antimicrobials should be administered to all patients regardless of the wound appearance. Antibiotic regimens should cover: E. corrodens, S. aureus, Haemophilus species, and anaerobes. Notably, E. corrodens is resistant to first-generation cephalosporins, macrolides, clindamycin, and aminoglycosides. Adequate agents include amoxicillin-clavulanate, ampicillin-sulbactam, carbapenems, and doxycyline. Intravenous antibiotics are preferred in clenched-fist injuries.
|AnswerA=Cefazolin
|AnswerA=Cefazolin
|AnswerAExp=Incorrect - Agents lacking activity against Eikenella corrodens should generally be avoided. These include erythromycin, clindamycin, beta-lactamase-resistant penicillins, and first-generation cephalosporins.
|AnswerAExp=Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Cefazolin does not cover anaerobic organisms or Eikenella species.
|AnswerB=Dicloxacillin
|AnswerB=Dicloxacillin
|AnswerBExp=Incorrect - Agents lacking activity against Eikenella corrodens should generally be avoided. These include erythromycin, clindamycin, beta-lactamase-resistant penicillins, and first-generation cephalosporins.
|AnswerBExp=Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Dicloxacillin lacks  Eikenella coverage.
|AnswerC=Erythromycin
|AnswerC=Erythromycin
|AnswerCExp=Incorrect - Agents lacking activity against Eikenella corrodens should generally be avoided. These include erythromycin, clindamycin, beta-lactamase-resistant penicillins, and first-generation cephalosporins.
|AnswerCExp=Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Erythromycin lacks coverage for all three.
|AnswerD=Clindamycin
|AnswerD=Clindamycin
|AnswerDExp=Incorrect - Agents lacking activity against Eikenella corrodens should generally be avoided. These include erythromycin, clindamycin, beta-lactamase-resistant penicillins, and first-generation cephalosporins.
|AnswerDExp=Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Although clindamycin has anerobic and staphylococcal coverage, it does not cover Eikenella.
|AnswerE=Amoxicillin-Clavulanate
|AnswerE=Amoxicillin-Clavulanate
|AnswerEExp=Correct - Amoxicillin-Clavulanate may be used as the primary regimen for human bite wounds caused by E. corrodens infeciton.
|AnswerEExp=Amoxicillin-Clavulanate may be used for post-exposure prophylaxis in cases of human bite wounds. It has adequate coverage for Eikenella Corrodens, Staphylococcus aureus (MSSA), and anaerobic organisms.
|EducationalObjectives=Prophylactic antimicrobials should be administered to all patients with human bite injuries. Antibiotic regimens should cover: E. corrodens, S. aureus, Haemophilus species, and anaerobes. Adequate agents include amoxicillin-clavulanate, ampicillin-sulbactam, carbapenems, and doxycyline.
|References=Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005;41(10):1373-406.<br>
Decker MD. Eikenella corrodens. Infect Control. 1986;7(1):36-41.
 
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=Eikenella corrodens
|WBRKeyword=Eikenella corrodens, Human bite injuries, Bite injuries, Clenched fist injuries, Antibiotics, Prophylaxis, Emergency,
|Approved=No
|Approved=Yes
}}
}}

Revision as of 18:07, 12 August 2015
Author PageAuthor::Gerald Chi (Reviewed by Serge Korjian)
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category SubCategory::Dermatology
Prompt [[Prompt::A 55-year-old man presents to the emergency department after being bitten by his brother during a domestic dispute. On physical examination, the physician notices a 3 by 3 inch wound on his arm lined by human teeth marks. What is the most appropriate agent to prevent infection of the wound in this case?]]
Answer A AnswerA::Cefazolin
Answer A Explanation AnswerAExp::Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Cefazolin does not cover anaerobic organisms or Eikenella species.
Answer B AnswerB::Dicloxacillin
Answer B Explanation AnswerBExp::Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Dicloxacillin lacks Eikenella coverage.
Answer C AnswerC::Erythromycin
Answer C Explanation AnswerCExp::Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Erythromycin lacks coverage for all three.
Answer D AnswerD::Clindamycin
Answer D Explanation [[AnswerDExp::Agents that lack anaerobic coverage as well as coverage against Eikenella corrodens, Haemophilus species, and Staphylococcus aureus are not appropriate for prophylaxis. Although clindamycin has anerobic and staphylococcal coverage, it does not cover Eikenella.]]
Answer E AnswerE::Amoxicillin-Clavulanate
Answer E Explanation AnswerEExp::Amoxicillin-Clavulanate may be used for post-exposure prophylaxis in cases of human bite wounds. It has adequate coverage for Eikenella Corrodens, Staphylococcus aureus (MSSA), and anaerobic organisms.
Right Answer RightAnswer::E
Explanation [[Explanation::Human bite wounds can be divided into 2 different types: occlusive injuries, defined as a wound from a direct bite, or clenched-fist injuries, defined as a wound from a fist striking teeth. Bacteria associated with human bite injuries are usually part of the oral flora and include viridans streptococci, staphylococci, anaerobic organisms (Fusobacterium nucleatum, Prevotella, peptostreptococci), and Eikenella corrodens. E. corrodens is a facultatively anaerobic, pleomorphic bacillus that requires ample carbon dioxide concentrations to thrive. E. corrodens is part of the normal flora of the oral cavity and the upper respiratory tract. E. corrodens infections are common in untreated human bite wounds, especially clenched fist injuries. E. corrodens infections typically progress slowly and can manifest clinically one to two weeks after inoculation. Complications include osteomyelitis, loss of joint function, and bacteremia with endocarditis. General treatment of human bite wounds includes irrigation and topical wound cleansing, however, unlike animal bites, prophylactic antimicrobials should be administered to all patients regardless of the wound appearance. Antibiotic regimens should cover: E. corrodens, S. aureus, Haemophilus species, and anaerobes. Notably, E. corrodens is resistant to first-generation cephalosporins, macrolides, clindamycin, and aminoglycosides. Adequate agents include amoxicillin-clavulanate, ampicillin-sulbactam, carbapenems, and doxycyline. Intravenous antibiotics are preferred in clenched-fist injuries.

Educational Objective: Prophylactic antimicrobials should be administered to all patients with human bite injuries. Antibiotic regimens should cover: E. corrodens, S. aureus, Haemophilus species, and anaerobes. Adequate agents include amoxicillin-clavulanate, ampicillin-sulbactam, carbapenems, and doxycyline.
References: Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005;41(10):1373-406.
Decker MD. Eikenella corrodens. Infect Control. 1986;7(1):36-41.]]

Approved Approved::Yes
Keyword WBRKeyword::Eikenella corrodens, WBRKeyword::Human bite injuries, WBRKeyword::Bite injuries, WBRKeyword::Clenched fist injuries, WBRKeyword::Antibiotics, WBRKeyword::Prophylaxis, WBRKeyword::Emergency
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