What is the treatment for Citrobacter (a type of gram-negative bacteria) koseri Urinary Tract Infection (UTI)?

Treatment of Citrobacter koseri Urinary Tract Infection

For Citrobacter koseri UTI, treatment should be based on antimicrobial susceptibility testing with fluoroquinolones, aminoglycosides, or carbapenems as preferred options depending on infection severity and resistance patterns.

Initial Assessment and Classification

• Determine if the UTI is uncomplicated (limited to bladder/cystitis) or complicated (involving upper urinary tract/pyelonephritis or with complicating factors)
• Obtain urine culture and susceptibility testing before initiating therapy
• Assess for risk factors for resistance (recent hospitalization, previous antibiotic exposure, immunocompromised state)

Treatment Algorithm

Uncomplicated C. koseri UTI (Cystitis)

1. First-line options (pending susceptibility):

   • Fluoroquinolones (e.g., Levofloxacin 750mg daily for 5 days) 1
   • Single-dose aminoglycoside (if susceptible) 2

2. Alternative options (based on susceptibility):

   • Trimethoprim-sulfamethoxazole (160/800mg twice daily for 5-7 days) if susceptible 3
   • Nitrofurantoin (100mg twice daily for 5-7 days) - only for lower UTI and if susceptible 4
   • Fosfomycin (3g single dose) - only for lower UTI and if susceptible 4

Complicated C. koseri UTI (Pyelonephritis or with complicating factors)

1. First-line options:

   • Fluoroquinolones (e.g., Levofloxacin 750mg daily for 7-10 days) 1
   • Carbapenems (e.g., Meropenem-vaborbactam 4g IV q8h or Imipenem-cilastatin-relebactam 1.25g IV q6h) 2

2. Alternative options (based on susceptibility):

   • Ceftazidime-avibactam 2.5g IV q8h (for resistant strains) 2
   • Aminoglycosides (e.g., Amikacin, Gentamicin) - consider in combination for severe infections 2
   • Piperacillin-tazobactam (3.375-4.5g IV every 6 hours) 4

Special Considerations

For Multidrug-Resistant C. koseri

• Ceftazidime-avibactam 2.5g IV q8h is recommended for complicated UTI caused by carbapenem-resistant Enterobacterales (CRE) 2
• Meropenem-vaborbactam 4g IV q8h or imipenem-cilastatin-relebactam 1.25g IV q6h are recommended for complicated UTI caused by CRE 2
• Plazomicin 15 mg/kg IV q12h is recommended for complicated UTI due to CRE 2

Duration of Therapy

• Uncomplicated lower UTI: 5-7 days
• Complicated UTI: 7-10 days
• Severe infections or bacteremia: 10-14 days 4

Monitoring and Follow-up

• Clinical improvement should be seen within 48-72 hours
• For patients whose symptoms don't resolve by end of treatment or recur within 2 weeks, repeat urine culture with susceptibility testing 4
• No routine post-treatment cultures needed if symptoms resolve

Important Caveats

• C. koseri has inherent resistance to ampicillin and may develop resistance to beta-lactams and aminoglycosides 5, 6
• Fluoroquinolones should be used judiciously due to increasing resistance rates and risk of adverse effects 7
• Nitrofurantoin and fosfomycin should only be used for lower UTI (cystitis), not for pyelonephritis or systemic infection 4
• Aminoglycosides are particularly effective for UTIs due to their high concentration in urine, but monitor renal function when using 2
• For severe infections, consider combination therapy until susceptibility results are available 7

The choice of antibiotic should ultimately be guided by local resistance patterns and individual susceptibility testing results, as C. koseri can develop multiple resistance mechanisms 7, 6.