What is the recommended treatment for a urinary tract infection (UTI) caused by Aerococcus urinae?

Treatment of Urinary Tract Infection Caused by Aerococcus urinae

For urinary tract infections caused by Aerococcus urinae, penicillin, amoxicillin, or nitrofurantoin should be used as first-line treatment options based on their demonstrated efficacy and safety profiles. 1, 2

Recommended Treatment Algorithm

First-Line Options:

1. Nitrofurantoin

   • Dosage: 100mg twice daily
   • Duration: 5-7 days
   • Considerations: Preferred for uncomplicated lower UTIs; achieved clinical and microbiological success in 71-76% of A. urinae UTI cases 2

2. Amoxicillin/Penicillin

   • Amoxicillin dosage: 500mg three times daily
   • Duration: 7 days for uncomplicated cases
   • Considerations: Excellent activity against A. urinae with low MICs 3

3. Fosfomycin

   • Dosage: 3g single dose
   • Considerations: Convenient single-dose administration for uncomplicated lower UTIs 4

For Complicated UTIs:

1. Intravenous Options:

   • Penicillin G or Ampicillin
   • Ceftriaxone: 1-2g daily 5
   • Duration: 7-14 days 6

2. For Severe Infections (bacteremia, endocarditis, spondylodiscitis):

   • Combination therapy with penicillin/amoxicillin plus gentamicin is recommended
   • Duration: At least 2 weeks of IV therapy followed by oral step-down therapy 3, 7

Treatment Selection Based on Clinical Presentation

Uncomplicated Lower UTI:

• Nitrofurantoin or amoxicillin as first-line therapy
• Fosfomycin as an alternative single-dose option
• Duration: 5-7 days

Complicated UTI:

• Intravenous therapy with penicillin/ampicillin or ceftriaxone
• Consider adding an aminoglycoside for synergistic effect
• Duration: 7-14 days 6

Bacteremia or Invasive Infection:

• Combination therapy with penicillin/ampicillin plus gentamicin
• Time-kill studies demonstrate rapid bactericidal activity with this combination 3
• Duration: 2-4 weeks depending on clinical response and infection site

Important Considerations

Antimicrobial Susceptibility Testing

• Always perform susceptibility testing as part of urine culture when A. urinae is isolated 1, 5
• A. urinae generally shows low MICs to penicillins, cephalosporins, and vancomycin 3

Risk Factors to Assess

• Advanced age (median age 82 years in recent cohort) 5
• Urologic conditions (cancer, retention, indwelling catheters) 1
• Multiple comorbidities

Monitoring and Follow-up

• Assess clinical response within 48-72 hours
• Obtain follow-up urine culture to confirm microbiological cure in complicated cases
• Evaluate for underlying urological abnormalities, especially in patients without obvious predisposing factors 7

Special Situations

Penicillin Allergy

• Vancomycin is the most appropriate alternative
• Consider adding gentamicin for synergistic effect in severe infections 3

Urosepsis

• Recent data shows A. urinae can cause urosepsis if untreated 5
• Prompt initiation of appropriate antimicrobial therapy is critical
• Consider combination therapy with penicillin/ampicillin plus gentamicin

Prevention of Recurrence

• Address underlying urological abnormalities
• Consider increased fluid intake and other non-antimicrobial preventive measures for patients with recurrent UTIs 4

A. urinae is an emerging pathogen increasingly recognized in UTIs, particularly in older adults with comorbidities. Prompt identification and targeted antimicrobial therapy based on susceptibility testing are essential to prevent progression to invasive disease.