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

Treatment of Aerococcus Species UTI

Nitrofurantoin 100 mg orally every 6 hours for 7 days is the recommended first-line treatment for uncomplicated Aerococcus urinae cystitis, achieving clinical and microbiological cure in approximately 71-76% of cases. 1

Organism-Specific Considerations

Aerococcus urinae vs. Aerococcus sanguinicola

• A. urinae is the more common species causing UTI and responds better to standard oral antibiotics 1, 2
• A. sanguinicola has lower cure rates with nitrofurantoin (42-50% clinical success) and may require alternative agents 1
• Both species are frequently misidentified as streptococci or staphylococci on routine culture, leading to underdiagnosis 2
• MALDI-TOF mass spectrometry provides accurate identification when available 2

Treatment Algorithm by Clinical Presentation

Uncomplicated Cystitis (Lower UTI)

First-line options:

• Nitrofurantoin 100 mg orally every 6 hours for 7 days - most validated option for A. urinae 1
• Pivmecillinam - effective specifically for A. urinae cystitis 1
• Amoxicillin 500 mg orally every 8 hours for 7 days - alternative based on susceptibility 3

Key clinical pitfall: Nitrofurantoin shows significantly reduced efficacy for A. sanguinicola compared to A. urinae, so species identification matters 1

Complicated UTI or Pyelonephritis

• Ciprofloxacin demonstrated success in patients with pyelonephritis caused by aerococci 1
• Treatment duration should extend to 10-14 days for complicated infections 4
• Avoid empiric fluoroquinolones if local resistance exceeds 10% or recent fluoroquinolone exposure 4

Critical caveat: Uncertainty exists about fluoroquinolone effectiveness on aerococci despite clinical success in some studies, so obtain susceptibility testing 2

Catheter-Associated Aerococcal UTI

• Replace the catheter if it has been in place ≥2 weeks before initiating treatment 4
• Obtain urine culture from the freshly placed catheter prior to antibiotics 4
• Treatment duration: 7 days for prompt symptom resolution, 10-14 days for delayed response 4
• Consider 5-day levofloxacin 750 mg for non-severely ill patients with CA-UTI 4

Invasive Infections (Bacteremia/Endocarditis)

• Penicillin or ampicillin PLUS an aminoglycoside for serious infections 2, 5
• This combination is critical for endocarditis, which carries significant mortality risk 2, 5
• Close monitoring required as aerococci can cause fatal invasive disease, especially in elderly men with urologic abnormalities 2, 3

Antibiotics to Avoid

Do NOT use as empiric therapy:

• Trimethoprim-sulfamethoxazole - uncertain effectiveness against aerococci 2
• First and second-generation cephalosporins - generally ineffective 4
• Fluoroquinolones have unpredictable activity despite some clinical success 2

Essential Pre-Treatment Steps

• Always obtain urine culture with susceptibility testing before initiating therapy, as resistance patterns are unpredictable 4, 3
• Differentiate true infection from colonization - do not treat asymptomatic bacteriuria 4
• Consider patient risk factors: aerococcal UTI predominantly affects elderly patients with urologic abnormalities, chronic retention, or indwelling catheters 2, 3

Special Population Considerations

Elderly men with multimorbidity:

• Higher risk for progression to bacteremia 2, 3
• Prompt culture-specific treatment critical to prevent invasive disease 3
• Evaluate for urologic malignancy or obstruction as predisposing factors 3

Patients with urologic cancer or chronic retention:

• Consider longer treatment duration (10-14 days) even for apparent cystitis 4
• Address underlying urologic abnormality as definitive management 4