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Urinary Tract Infection (Uti) 2

Urinary tract infection (UTI)
microbiology

Question

Vignette: A 45-year-old woman presents to the clinic with complaints of frequent urination, lower abdominal pain, and a burning sensation during urination for the past two days. Her temperature is 38.5°C (101.3°F). Urine analysis shows numerous leukocytes, moderate leukocyte esterase, and positive nitrite. Gram staining of the urine sample shows gram-negative rods. Which of the following is the most likely causative organism?

Choices

A) Escherichia coli

B) Klebsiella pneumoniae

C) Proteus mirabilis

D) Staphylococcus saprophyticus

E) Streptococcus agalactiae

Answer

A) Escherichia coli

Explanation

The patient's symptoms of frequent urination, lower abdominal pain, and dysuria, along with the laboratory findings of pyuria and bacteriuria, are indicative of a urinary tract infection (UTI). In sexually active women, the most common cause of UTIs is Escherichia coli, accounting for up to 70-95% of all uncomplicated UTIs. E. coli is a gram-negative rod that can be identified by its ability to ferment lactose on MacConkey agar, producing pink colonies. It is also a nitrite producer, which is what gives a positive nitrite test in urine analysis. Nitrite is not commonly found in urine; its presence suggests that bacteria have converted urinary nitrate to nitrite. Other gram-negative rods such as klebsiella pneumoniae and Proteus mirabilis can also cause UTIs but are not as common as E. coli. staphylococcus saprophyticus and streptococcus agalactiae are gram-positive cocci and are less common causes of UTI, particularly in non-pregnant women.

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