WBR0381

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Genitourinary
Prompt	[[Prompt::A 45-year-old female presents to the ER with complaints of a fever and flank pain that began on the same day. Upon further questioning, the patient admits to recent onset dysuria and urinary frequency, for which she did not seek medical care. Her temperature is 38.9 °C, her heart rate 96 beats per minute, and blood pressure 116/88 mmHg. Physical examination reveals a positive Murphy’s punch sign (costovertebral angle tenderness). You diagnose her with acute pyelonephritis and take urine cultures and initiate appropriate antibiotic therapy. 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? ]]
Answer A	AnswerA::Capsule
Answer A Explanation	AnswerAExp::The capsule is a virulence factor of ''E. coli'' that causes pneumonia and meningitis in neonates. It has no significant role in acute pyelonephritis.
Answer B	AnswerB::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.
Answer C	AnswerC::Lipopolysaccaride (LPS) endotoxin
Answer C Explanation	AnswerCExp::The LPS endotoxin is a virulence factor of ''E. coli'' that causes 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::Escherichia coli (E. coli), the most common causative agent of acute pyelonephritis, is a lactose-fermenting gram-negative, catalase-positive rod, whivh grows on the 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 fimbriae, adhesions that are implicated in cystitis and acute pyelonephritis. Fimbriae are present in nearly all strains of E. coli that cause pyelonephritis. Educational Objective: E. coli is a lactose-fermenting gram-negative, catalase-positive rod, which grows on EMB agar and appears as green metallic sheen. The virulence factor responsible for pyelonephritis in E. coli is its fimbriae. References: Stapleton A. Novel mechanism of P-fimbriated Escherichia coli virulence in pyelonephritis. J Am Soc Nephrol. 2005;16(12):3458-3460.]]
Approved	Approved::Yes
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