What is the recommended treatment for a patient with a urine culture showing Enterobacter cloacae (E. cloacae) infection, with known antibiotic susceptibility results?

Treatment of Urinary Tract Infection Caused by Enterobacter cloacae

For a urinary tract infection caused by Enterobacter cloacae with the provided susceptibility results, ceftriaxone is the recommended first-line treatment due to its demonstrated susceptibility and excellent clinical efficacy for complicated UTIs.

Understanding the Pathogen and Susceptibility Results

The urine culture shows >100,000 CFU/mL of Enterobacter cloacae, indicating a significant infection. The susceptibility testing reveals:

• Resistant to: Amoxicillin/clavulanate, Ampicillin, Cefazolin
• Susceptible to: Ceftazidime, Ceftriaxone, Cefuroxime, Ciprofloxacin, Gentamicin, Imipenem, Levofloxacin, Meropenem, Piperacillin/tazobactam, Tetracycline, Tobramycin, Trimethoprim/sulfamethoxazole
• Intermediate susceptibility to: Nitrofurantoin

Treatment Recommendations

First-line Options:

1. Ceftriaxone 1-2g IV/IM daily for 7-10 days

   • Excellent susceptibility profile for this isolate
   • Recommended by guidelines for complicated UTIs caused by Enterobacteriaceae 1
   • High urinary concentration and once-daily dosing

2. Alternative options (if parenteral therapy not preferred):

   • Ciprofloxacin 500mg PO twice daily for 7-10 days
   • Levofloxacin 750mg PO daily for 7-10 days 2
   • Trimethoprim/sulfamethoxazole 160/800mg PO twice daily for 7-10 days

Special Considerations:

• Avoid amoxicillin/clavulanate and ampicillin as the organism is resistant
• Avoid nitrofurantoin due to intermediate susceptibility and poor tissue penetration beyond the bladder
• Carbapenems (imipenem, meropenem) should be reserved for more severe infections or when other options cannot be used 3

Treatment Duration

• Complicated UTI: 7-10 days of therapy 1
• Uncomplicated UTI: 5-7 days may be sufficient if symptoms resolve quickly
• Male UTIs are considered complicated by definition and typically require 7-14 days of treatment 1

Monitoring and Follow-up

• Clinical improvement should be seen within 48-72 hours
• Follow-up urine culture is not routinely recommended if symptoms resolve
• If symptoms persist beyond 72 hours, consider:
  • Repeat urine culture
  • Imaging to rule out complications (abscess, obstruction)
  • Possible switch to alternative antibiotic

Rationale for Recommendation

Enterobacter cloacae is an important nosocomial pathogen that has emerged as a clinically significant cause of UTIs 4. This organism is known for its ability to develop resistance, particularly through production of AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs).

Ceftriaxone is preferred because:

1. The isolate shows clear susceptibility
2. It achieves high urinary concentrations
3. It has demonstrated efficacy against Enterobacter species in clinical studies
4. Once-daily dosing improves compliance
5. It has less ecological impact on gut flora compared to fluoroquinolones

Studies have shown that appropriate antibiotic therapy based on susceptibility results significantly reduces the risk of treatment failure and breakthrough bacteremia in patients with Enterobacter infections 5.

Potential Pitfalls

1. Inducible resistance: Enterobacter species can develop resistance to cephalosporins during therapy through induction of AmpC β-lactamases. Monitor closely for clinical response.

2. Biofilm formation: E. cloacae has strong adhesion to urinary tract tissues 6, which may complicate treatment in patients with indwelling catheters or structural abnormalities.

3. Underlying conditions: Always evaluate for and address any urological abnormalities, obstruction, or foreign bodies that may contribute to persistent infection.

4. Empiric therapy: While awaiting culture results, empiric therapy should cover common uropathogens including potentially resistant Gram-negative organisms in patients with risk factors for resistance.

By following these evidence-based recommendations and selecting an appropriate antibiotic based on susceptibility testing, successful treatment of E. cloacae UTI can be achieved with minimal risk of treatment failure or recurrence.