What is the recommended treatment for Serratia marcescens (Gram-negative bacteria) urinary tract infection (UTI)?

Treatment of Serratia marcescens Urinary Tract Infection

For Serratia marcescens UTI, the recommended first-line treatment is cefotaxime or gentamicin, as these antibiotics have demonstrated the lowest resistance rates (0.6%) against this organism. 1

Antimicrobial Options for Serratia marcescens UTI

First-line Options:

• Aminoglycosides:
  • Gentamicin (excellent susceptibility profile with only 3/26 isolates showing resistance) 2
  • Amikacin (superior susceptibility with 0/21 isolates showing resistance) 2

Alternative Options:

• Carbapenems:

  • Meropenem (excellent bladder penetration) 3
  • Imipenem-cilastatin-relebactam for resistant strains 4

• Fluoroquinolones:

  • Levofloxacin (FDA-approved for complicated UTIs including those caused by Serratia marcescens) 5
  • Ciprofloxacin (should be reserved for cases where first-line agents cannot be used) 3

• Other options:

  • Trimethoprim-sulfamethoxazole (cotrimoxazole) for uncomplicated UTIs, though resistance has been observed (10/27 isolates) 2
  • Third-generation cephalosporins (note: resistance rates to ceftriaxone and ceftazidime were 22.7% and 19.6%, respectively) 1

For Resistant Strains:

• Ceftazidime-avibactam 2.5g IV q8h 4, 3
• Meropenem-vaborbactam 4g IV q8h 4, 3

Treatment Algorithm

1. For uncomplicated Serratia marcescens UTI:

   • Gentamicin or amikacin (if renal function permits)
   • Alternative: Trimethoprim-sulfamethoxazole (if susceptible)

2. For complicated Serratia marcescens UTI:

   • Gentamicin or amikacin plus third-generation cephalosporin 2
   • Alternative: Carbapenem (meropenem) monotherapy

3. For resistant Serratia marcescens UTI:

   • Ceftazidime-avibactam or meropenem-vaborbactam 4, 3

Duration of Treatment

• Uncomplicated UTI: 5-7 days
• Complicated UTI: 7-10 days
• Pyelonephritis: 10-14 days 3

Important Considerations

• Obtain culture and susceptibility testing before initiating treatment to guide appropriate antibiotic selection 3
• S. marcescens has intrinsic resistance to several antibiotics including penicillins, nitrofurantoin, and colistin 2
• Avoid nitrofurantoin despite it being a common first-line agent for other UTIs, as S. marcescens is inherently resistant 2
• Aminoglycoside monotherapy may be sufficient for uncomplicated UTIs, but combination therapy with a third-generation cephalosporin is recommended for invasive infections 2
• Monitor renal function when using aminoglycosides due to potential nephrotoxicity
• S. marcescens infections are often nosocomial and frequently associated with urinary catheters, so catheter removal or replacement should be considered when appropriate 6

Pitfalls to Avoid

• Failing to obtain cultures before initiating antibiotics
• Using nitrofurantoin, which is ineffective against S. marcescens
• Underestimating the potential for antibiotic resistance in S. marcescens
• Prescribing unnecessarily long courses of antibiotics, which increases the risk of adverse effects and resistance development 3
• Neglecting to address underlying factors such as urinary catheters or structural abnormalities that may contribute to infection persistence

By following this treatment approach and considering the unique resistance patterns of S. marcescens, clinicians can effectively manage UTIs caused by this organism while minimizing the risk of treatment failure and further resistance development.