What is the appropriate treatment for a patient with a urinary tract infection caused by Escherichia coli, given the antibiotic susceptibility testing results?

Treatment of Urinary Tract Infection Caused by Escherichia coli Based on Antibiotic Susceptibility Testing

Based on the antibiotic susceptibility results, nitrofurantoin is the most appropriate treatment for this urinary tract infection caused by Escherichia coli. 1

Interpretation of Urinalysis and Culture Results

• The urinalysis shows clear evidence of a urinary tract infection with:

  • Positive leukocyte esterase (3+)
  • Elevated WBCs (≥60/HPF)
  • Presence of bacteria (many)
  • Positive protein (1+) and blood (1+) 1

• The urine culture confirms a significant infection with >100,000 CFU/mL of Escherichia coli, which is the most common causative organism in urinary tract infections 1

• The antibiotic susceptibility testing shows:

  • Susceptible to: nitrofurantoin, cefazolin, cefepime, ceftazidime, ceftriaxone, imipenem, meropenem, piperacillin/tazobactam, trimethoprim/sulfamethoxazole
  • Resistant to: ciprofloxacin, levofloxacin, gentamicin
  • Intermediate susceptibility to: amoxicillin/clavulanate, ampicillin/sulbactam 1

Treatment Recommendations

First-line Treatment Options

1. Nitrofurantoin

   • Highly effective against this E. coli isolate (susceptible)
   • Recommended as first-line therapy for uncomplicated UTIs by guidelines
   • Achieves high concentrations in urine
   • Low risk of collateral damage to intestinal flora 1, 2

2. Trimethoprim/Sulfamethoxazole (TMP-SMX)

   • Susceptible based on testing
   • Effective for uncomplicated UTIs
   • Should be considered if nitrofurantoin is contraindicated 1

3. Cefazolin

   • Susceptible based on testing (MIC = 2)
   • Appropriate for treatment of this infection 1, 3

Duration of Treatment

• For uncomplicated UTI: 5-7 days of treatment is recommended 1
• For complicated UTI: 7-14 days of treatment is recommended (14 days for men when prostatitis cannot be excluded) 1
• If the patient becomes hemodynamically stable and afebrile for at least 48 hours, a shorter treatment duration (7 days) may be considered 1

Factors to Consider in Treatment Selection

• Local resistance patterns: The susceptibility testing shows fluoroquinolone resistance, which is becoming increasingly common in E. coli 1, 2

• Biofilm formation: E. coli can form biofilms which may contribute to persistence and recurrence of infection, making appropriate antibiotic selection and adequate treatment duration important 4, 5

• Virulence factors: E. coli possesses various virulence factors that enable it to cause UTIs, including adhesins, toxins, and iron-acquisition systems 4, 6

• Patient factors: Consider any history of allergies, renal function, pregnancy status, and other comorbidities when selecting antibiotics 1

Treatment Algorithm

1. For uncomplicated UTI:

   • First choice: Nitrofurantoin 100 mg twice daily for 5-7 days 1, 2
   • Alternative: TMP-SMX 160/800 mg twice daily for 5-7 days (if no contraindications) 1

2. For complicated UTI (presence of structural abnormalities, male gender, immunosuppression, diabetes, pregnancy, or healthcare-associated infection):

   • First choice: Cefazolin or other susceptible cephalosporin for 7-14 days 1
   • Alternative: TMP-SMX for 7-14 days 1

3. For catheter-associated UTI:

   • If catheter has been in place for >2 weeks, replace catheter before initiating antimicrobial therapy 1
   • Treat with susceptible antibiotic for 7 days if symptoms promptly resolve, or 10-14 days if response is delayed 1

Common Pitfalls to Avoid

• Fluoroquinolone use: Despite their historical popularity, fluoroquinolones should be avoided in this case due to demonstrated resistance (ciprofloxacin and levofloxacin) 1

• Untreated asymptomatic bacteriuria: Asymptomatic bacteriuria should not be treated except in specific circumstances (pregnancy, before urological procedures) 1

• Inadequate treatment duration: Too short a course may lead to treatment failure and recurrence, while unnecessarily prolonged treatment increases risk of resistance 1

• Failure to address underlying factors: Any anatomical or functional abnormalities contributing to the UTI should be addressed to prevent recurrence 1