Updated: 4/21/2015

Microbiology of Urinary Tract Infections

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Topic
 
 Bugs causing UTIs
Bug (Bacteria only)
Comments
E. coli #1 leading cause of UTI 
S. saprophyticus #2 leading cause of UTI, common in young, sexually active women
K. pneumoniae  
Proteus  
P. aeruginosa  Common cause in patients with indwelling catheters
Serratia  
Enterobacter cloacae  
E. faecalis  
  • Urinary tract infections
    • cystitis ("bladder infection")
      • dysuria
      • polyuria
      • suprapubic pain
      • WBCs in urine
        • no casts
      • systemic symptoms (e.g. fever) uncommon
    • pyelonephritis (infection reaches upper urinary tract or kidney)
      • fever
      • chills
      • flank pain / costovertebral angle (CVA) tenderness
      • WBC casts in urine
      • hematuria
  • Diagnosis
    • positive leukocyte esterase test = bacterial UTI
    • positive Nitrite test = Gram-Negative bacterial UTI
  • Predisposing factors
    • urinary catheterization
    • diabetes
    • pregnancy
    • kidney surgery
    • congenital defects
    • vesicoureteral reflux (urine flows from bladder back to ureters)
    • BPH
  • Epidemiology
    • women affected 10x more frequently than men
      • shorter urethra
      • proximity of urethra to anus
      • colonization of vagina by fecal flora
    • leading cause of UTIs is urinary catheters
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Questions (3)

(M1.MC.15.75) A 22-year-old sexually active female presents to the emergency department in severe pain. She states that she has significant abdominal pain that seems to worsen whenever she urinates. This seems to have progressed over the past day and is accompanied by increased urge and frequency. The emergency room physician obtains a urine dipstick which demonstrates the following:

Urine:
Specific gravity: 1.010
Leukocyte esterase: Positive
Protein: Trace
pH: 7.2
RBC: Negative
Nitrite: Negative.

A urease test is performed which is positive. What is most likely cause of UTI in this patient?
Tested Concept

QID: 106729
1

Klebsiella pneumoniae

12%

(23/200)

2

Staphylococcus saprophyticus

31%

(62/200)

3

Proteus mirabilis

26%

(51/200)

4

Escherichia coli

24%

(47/200)

5

Serratia marcescens

1%

(2/200)

M 2 D

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(M1.MC.15.75) A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms? Tested Concept

QID: 106704
1

Proteus mirabilis

2%

(1/47)

2

Klebsiella pneumoniae

2%

(1/47)

3

Escherichia coli

77%

(36/47)

4

Staphylococcus saprophyticus

11%

(5/47)

5

Enterobacter cloacae

2%

(1/47)

M 1 D

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Evidence (3)
Topic COMMENTS (6)
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