What is the appropriate treatment for a patient with a urinary tract infection (UTI) caused by Escherichia coli (E. coli) with a colony count of greater than 100,000 CFU/mL?

Treatment of E. coli Urinary Tract Infection with Antibiotic Resistance

Based on the urinalysis and culture results showing E. coli resistant to multiple antibiotics, nitrofurantoin is the recommended treatment for this urinary tract infection.

Analysis of the Urinalysis and Culture Results

The urinalysis shows multiple abnormal findings consistent with a urinary tract infection:

• Cloudy appearance
• Acidic pH (<5.0)
• 2+ occult blood
• 2+ protein
• 2+ leukocyte esterase
• Packed WBCs
• Many bacteria

The urine culture confirms:

• 100,000 CFU/mL of Escherichia coli

• Resistance to multiple antibiotics including:
  • Amoxicillin/clavulanate (I)
  • Ampicillin/sulbactam (I)
  • Cefazolin (R)
  • Cefepime (R)
  • Ceftazidime (R)
  • Ceftriaxone (R)
  • Ciprofloxacin (R)
  • Levofloxacin (R)
  • Trimethoprim/sulfa (R)
• Susceptibility to:
  • Gentamicin (S)
  • Imipenem (S)
  • Meropenem (S)
  • Nitrofurantoin (S)
  • Piperacillin/tazobactam (S)

Treatment Recommendation

First-line Treatment

• Nitrofurantoin 100 mg PO twice daily for 5 days 1, 2
  • Nitrofurantoin is susceptible per culture results
  • Achieves high urinary concentrations
  • Recommended by guidelines for uncomplicated UTIs
  • Low resistance rates compared to other oral options

Alternative Options (if nitrofurantoin is contraindicated)

1. Gentamicin - single daily dose (based on weight) for 5-7 days 1

   • Consider renal function before prescribing
   • Avoid if patient has renal impairment or is taking other nephrotoxic drugs

2. Fosfomycin 3g single dose 1, 2

   • Consider if susceptibility testing is available and confirms susceptibility

3. Carbapenems (imipenem or meropenem) 1

   • Reserve for severe infections or treatment failures
   • Should be avoided if possible due to antimicrobial stewardship concerns

Treatment Considerations

Duration of Therapy

• 5 days of nitrofurantoin is recommended for uncomplicated UTIs 1, 2
• Longer duration (7-14 days) may be needed if:
  • Symptoms of pyelonephritis are present
  • Patient has complicated UTI factors (structural abnormalities, immunocompromised)
  • Delayed clinical response 1

Monitoring and Follow-up

• Clinical improvement should be seen within 48-72 hours
• Consider follow-up urine culture only if:
  • Symptoms persist after completing therapy
  • Recurrent infections occur
  • Patient is at high risk for complications

Important Cautions

• Nitrofurantoin should not be used if:
  • CrCl <30 mL/min (inadequate urinary concentrations)
  • Symptoms of pyelonephritis/upper UTI are present (poor tissue penetration)
  • Patient is pregnant near term

Special Considerations for This Case

1. The E. coli isolate shows an ESBL (Extended-Spectrum Beta-Lactamase) pattern with resistance to multiple cephalosporins
2. Fluoroquinolones and trimethoprim-sulfamethoxazole are not options due to resistance
3. Nitrofurantoin remains effective against many ESBL-producing organisms and achieves high urinary concentrations
4. Carbapenems should be reserved for severe infections or treatment failures to preserve antimicrobial effectiveness 1

Practical Advice

• Ensure adequate hydration during treatment
• Complete the full course of antibiotics even if symptoms improve
• Advise patient about potential side effects of nitrofurantoin (nausea, discoloration of urine)
• Consider symptomatic relief with phenazopyridine if dysuria is severe

This treatment approach balances effectiveness against the resistant organism while practicing good antimicrobial stewardship by avoiding unnecessary use of broad-spectrum agents.