WBR0381
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| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Genitourinary |
| Prompt | [[Prompt::A 45-year-old woman presents to the emergency department with complaints of fever and flank pain for the past day. Upon further questioning, the patient admits to recent-onset dysuria and urinary frequency, for which she did not seek medical care. In the ED, her temperature is 38.9 °C (102 °F), her heart rate is 96/min, and blood pressure is 116/88 mmHg. Physical examination is remarkable for a positive Murphy’s punch sign (costovertebral angle tenderness). Urinalysis demonstrates hematuria and pyuria with casts. Urine samples are then sent for culture and antibiotic therapy is initiated. The next day, eosin methylene blue (EMB) agar demonstrates the growth of a specific bacterial strain as displayed in the image below. Which of the following virulence factors is implicated in this patient’s condition?
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| Answer A | AnswerA::Capsule |
| Answer A Explanation | AnswerAExp::The capsule is a virulence factor of ''E. coli'' that is implicated in pneumonia and neonatal meningitis. It has no significant role in acute pyelonephritis. |
| Answer B | AnswerB::P fimbriae |
| Answer B Explanation | [[AnswerBExp::E. coli is a a lactose-fermenting gram-negative, catalase-positive rod, which grows on EMB agar and appears as green metallic sheen. Expression of the virulence factor P fimbriae is important in the pathogenesis of acute pyelonephritis and cystitis.]] |
| Answer C | AnswerC::Lipopolysaccaride (LPS) endotoxin |
| Answer C Explanation | AnswerCExp::The LPS endotoxin is a virulence factor of ''E. coli'' that is implicated in septic shock. |
| Answer D | AnswerD::Streptolysin O |
| Answer D Explanation | AnswerDExp::Streptolysin O is a hemolytic toxin of group A streptococci; it is not usually found in ''E. coli''. |
| Answer E | AnswerE::Erythrogenic toxin |
| Answer E Explanation | [[AnswerEExp::Erythrogenic toxin is produced by Streptococcus pyogenes and is implicated in scarlet fever. The toxin itself is encoded in a lysogenic phage by specialized transduction.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient is diagnosed with acute pyelonephritis. The patient's history of recent dysuria and urinary frequency with worsening symptoms (flank pain and fever), along with costovertebral angle tenderness on physical examination and pyuria with casts on urinalysis, is highly suggestive of acute pyelonephritis (of note, Murphy punch sign is an alternative name for costovertebral angle tenderness and should not be confused with Murphy sign, which is a physical examination sign of cholecystitis). Escherichia coli (E. coli) that express P fimbriae are the most common causative agent of acute pyelonephritis and cystitis. E. coli is a lactose-fermenting gram-negative, catalase-positive rod that grows on selective EMB agar. As depicted in the image above, metallic green sheen is characteristic of E. coli strains grown on EMB. E. coli contains several virulence factors, such as P fimbriae, which are proteinaceous appendages on bacterial surfaces that mediate the adhesion of E. coli to the apical surface of the uroepithelium (bind to Gal-alpha[1 to 4] Gal disaccaride). The presence of P fimbriae is crucial for E. coli ascending along the urogenital tract. Educational Objective: E. coli is a lactose-fermenting, catalase-positive, gram-negative rod, which grows on EMB agar and appears as green metallic sheen. The virulence factor responsible for pyelonephritis in E. coli is P fimbriae. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Fimbriae, WBRKeyword::P fimbriae, WBRKeyword::E. coli, WBRKeyword::Escherichia coli, WBRKeyword::Acute pyelonephritis, WBRKeyword::Pyelonephritis, WBRKeyword::Cystitis, WBRKeyword::Dysuria, WBRKeyword::Urinary frequency, WBRKeyword::Pathogenesis, WBRKeyword::Pathophysiology, WBRKeyword::Mechanism of action |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
