WBR0473
Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]] |
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Exam Type | ExamType::USMLE Step 1 |
Main Category | MainCategory::Microbiology |
Sub Category | SubCategory::Cardiology |
Prompt | [[Prompt::A 67-year-old woman presents to the emergency department for unremitting high-grade fever and left leg pain. The patient explains that she had a left total knee replacement 5 months ago. The patient is admitted and blood cultures are withdrawn. The next day, blood cultures grow a non-motile organism. Which of the following pathogens is most likely responsible for the patient's condition?]] |
Answer A | AnswerA::''Streptococcus bovis'' |
Answer A Explanation | AnswerAExp::''S. bovis'' infection is often associated with colon cancer. |
Answer B | AnswerB::''S. pyogenes'' |
Answer B Explanation | AnswerBExp::''S. pyogenes''' commonly cause impetigo and pharyngitis. They are not classically associated with prosthetic infections following total knee replacement. |
Answer C | AnswerC::Neisseria gonorrhea |
Answer C Explanation | AnswerCExp::''N. gonorrhea'' is a sexually transmitted infection that can cause infectious arthritis. |
Answer D | AnswerD::''Pseudomonas aeruginosa'' |
Answer D Explanation | AnswerDExp::''P. aeruginosa'' may be an infectious cause of a complicated total knee replacement. However, ''P. aeroginosa'' is a motile organism. |
Answer E | AnswerE::''Staphylococcus epidermidis'' |
Answer E Explanation | AnswerEExp::''S. epidermidis'' is a gram-positive, catalase-positive, coagulase-negative non-motile organism that is commonly associated with infections following prosthetic implant due to its ability to form antibiotic-resistant biofilms. |
Right Answer | RightAnswer::E |
Explanation | [[Explanation::Infection of an implanted foreign prosthetic material is a relatively common complication. Staphylococcus epidermidis infection is a particularly significant complication that is associated with prosthetic material. S. epidermidis is a gram-positive coagulase-negative non-motile organism that causes biofilms that grow on surgical implants or catheters. S. epidermidis is a catalase-positive, coagulase-negative, facultative anaerobe. It has a weak positive reaction to nitrate reduction test. Also, S. epidermidis is sensitive to novobiocin. In contrast, S. aureus is coagulase-positive and S. saprophyticus is novobiocin-resistant. An important virulence factor of S. epidermidis is its surface proteins that lead to the formation of antibiotic-resistant biofilms on plastic devices. Treatment of S. epidermidis usually requires administration of antibiotics along with surgical removal of the implanted device. Educational Objective: S. epidermidis is a gram-positive, catalase-positive, coagulase-negative non-motile organism that is commonly associated with infections following prosthetic implant due to its ability to form antibiotic-resistant biofilms. |
Approved | Approved::Yes |
Keyword | WBRKeyword::Staphylococcus, WBRKeyword::Epidermidis, WBRKeyword::Staphylococcus epidermidis, WBRKeyword::Total knee replacement, WBRKeyword::Biofilms, WBRKeyword::Prosthetic device, WBRKeyword::Prosthetic implant, WBRKeyword::Gram, WBRKeyword::Catalase, WBRKeyword::Coagulase, WBRKeyword::Motile, WBRKeyword::Organism, WBRKeyword::Bacteria, WBRKeyword::Bacterial infection, WBRKeyword::Fever, WBRKeyword::Leg pain |
Linked Question | Linked:: |
Order in Linked Questions | LinkedOrder:: |