What is the recommended antibiotic treatment for a patient with a urinary tract infection (UTI) showing significant bacterial loads of Escherichia coli (E. coli) and Staphylococcus aureus (Staph aureus)?

Treatment of UTI with E. coli and Staphylococcus aureus

For a urinary tract infection with significant bacterial loads of E. coli (70,000 CFU/mL) and Staphylococcus aureus (>100,000 CFU/mL), empiric treatment with ciprofloxacin is recommended, followed by targeted therapy based on culture and sensitivity results.

Initial Assessment and Management

Significance of Mixed Infection

• The presence of both E. coli and S. aureus in significant quantities represents a true polymicrobial UTI, which is uncommon in uncomplicated cases
• S. aureus in urine is clinically significant and associated with:
  • Higher risk of subsequent bacteremia (13% of patients) 1
  • Potential for persistent colonization (58% remain positive at ≥2 months) 1
  • Risk of invasive staphylococcal infection up to 12 months later 1

Empiric Antibiotic Selection

1. First-line recommendation: Ciprofloxacin

   • Effective against both E. coli and S. aureus 2
   • FDA-approved for UTIs caused by both organisms 2
   • Dosing: 500 mg orally twice daily for uncomplicated UTI or 750 mg twice daily for complicated UTI

2. Alternative option: Trimethoprim-sulfamethoxazole (TMP-SMX)

   • Effective against many urinary pathogens including E. coli 3
   • Consider local resistance patterns before using

Duration of Therapy

• 7 days is the recommended duration for patients with prompt symptom resolution 4
• 10-14 days for patients with delayed response 4
• Consider longer course (10-14 days) due to:
  • Presence of S. aureus, which increases risk of complications 4, 1
  • Polymicrobial nature of the infection

Special Considerations

Catheter-Associated UTI Considerations

• If infection is catheter-associated and catheter has been in place for ≥2 weeks:
  • Replace catheter before starting antibiotics if continued catheterization is necessary 4
  • Obtain culture from newly placed catheter 4

Follow-up Management

1. Repeat urine culture after completion of therapy to confirm clearance of both organisms
2. Monitor for signs of bacteremia or metastatic infection, particularly with S. aureus
3. Consider urologic evaluation to rule out structural abnormalities, especially in:
   • Males
   • Patients with recurrent UTIs
   • Patients with S. aureus in urine (unusual pathogen)

Antibiotic Stewardship Considerations

• De-escalate to targeted therapy based on culture and sensitivity results 4
• Avoid prolonged courses beyond recommended duration 4, 5
• Consider local resistance patterns when selecting empiric therapy 6

Cautions and Pitfalls

• Do not dismiss S. aureus as a contaminant in this case due to the high colony count (>100,000 CFU/mL)
• S. aureus bacteriuria can lead to subsequent invasive infection, with 8% of patients developing late-onset bacteremia 1
• Resistance transfer between E. coli and S. aureus can occur in the urinary tract, potentially complicating treatment 7
• Ensure adequate source control if there are complicating factors such as obstruction or abscess 4

By following these recommendations, you can effectively treat this polymicrobial UTI while minimizing the risk of complications and recurrence.