Treatment of Aerococcus urinae Infections
For uncomplicated urinary tract infections caused by Aerococcus urinae, treat with penicillin, amoxicillin, or nitrofurantoin; for bacteremia and endocarditis, use ampicillin or penicillin G (with or without gentamicin) for 2-4 weeks and 4-6 weeks respectively, with consideration for valve replacement in endocarditis cases.
Uncomplicated Urinary Tract Infections
For simple UTIs caused by A. urinae, the treatment approach is straightforward:
- First-line agents: Penicillin, amoxicillin, or nitrofurantoin 1
- Duration: Standard UTI treatment courses (typically 7-14 days based on clinical response)
- Key consideration: A. urinae demonstrates 100% susceptibility to penicillin G and 98.9% susceptibility to ceftriaxone 2, making beta-lactams highly reliable
Critical caveat: A. urinae is inherently resistant to sulphamethoxazole, and there are methodological problems determining trimethoprim sensitivity 3. Additionally, fluoroquinolone resistance is common (only 76.8% susceptibility to levofloxacin 2), so avoid empiric fluoroquinolone use despite their typical role in complicated UTIs per general guidelines 4.
Complicated Urinary Tract Infections
For complicated UTIs (males, elderly, urologic abnormalities, indwelling catheters):
- Preferred agent: Ampicillin is the safest treatment option 3
- Alternative: Ceftriaxone given high susceptibility rates
- Duration: 14 days minimum, adjusted based on clinical response
- Avoid: Fluoroquinolones due to resistance patterns, despite their recommendation in general cUTI guidelines 4
Bacteremia Without Endocarditis
When A. urinae causes bloodstream infection without endocarditis:
- Treatment regimen: Ampicillin or penicillin G
- Duration: 2 weeks of therapy demonstrated good outcomes 5
- Mortality: 30-day all-cause mortality is 17%, 3-month mortality 24% 5
- Source control: Essential—address underlying urologic pathology (obstruction, retention, catheter removal)
Infective Endocarditis
Endocarditis caused by A. urinae requires aggressive management:
Antibiotic Therapy
Recommended regimen (adapting from AHA guidelines for similar organisms 6):
- Penicillin G 24 million units/24h IV continuously or in 4-6 divided doses for 4-6 weeks
- Plus gentamicin 3 mg/kg/24h IV/IM in single daily dose for 2 weeks (synergy demonstrated 3)
- Alternative: Ampicillin 2g IV every 4 hours plus gentamicin (same dosing)
- For penicillin allergy: Vancomycin 30 mg/kg/24h IV in 2 divided doses for 6 weeks (gentamicin not needed with vancomycin 6)
Duration Considerations
The evidence shows variability:
- Traditional approach: 6 weeks for native valve, per AHA guidelines for similar organisms 6
- Emerging data: 4 weeks may be sufficient with good outcomes 5
- Practical recommendation: Use 4-6 weeks based on clinical response, vegetation size, and complications
Surgical Intervention
Indications for valve replacement:
- Severe valvular regurgitation (common with A. urinae endocarditis 7, 8)
- Large vegetations (>10mm)
- Septic embolization (occurs in approximately one-third of cases 5, 7)
- Heart failure
- Persistent bacteremia despite appropriate antibiotics
Important caveat: Cerebral septic emboli with hemorrhagic transformation may temporarily contraindicate cardiopulmonary bypass 7. In such cases, extend antibiotic therapy duration and delay surgery 2-4 weeks if hemodynamically stable.
Risk Stratification for Endocarditis
When A. urinae bacteremia is identified, assess endocarditis risk using the DENOVA score:
- Score ≥3: 100% sensitive, 89% specific for endocarditis 5
- Additional high-risk features: Symptoms >7 days (OR 105), septic emboli (OR 71), younger age (<70 years) 5
- Perform echocardiography (preferably TEE) in all bacteremic patients, especially with DENOVA ≥3
Patient Population Considerations
A. urinae infections predominantly affect:
- Elderly males (median age 80-82 years) 2, 5
- Urologic risk factors: Benign prostatic hypertrophy, chronic retention, indwelling catheters, recurrent UTIs 7
- Endocarditis patients: Tend to be younger (median 66 years) than those with simple bacteremia 5
Diagnostic Pitfalls
- A. urinae is frequently misidentified as "other Gram-positive cocci" or confused with streptococci/staphylococci 2, 3
- MALDI-TOF mass spectrometry has dramatically improved identification 2, 3
- Always request species-level identification and susceptibility testing when Gram-positive cocci are isolated from urine or blood cultures in elderly males with urologic conditions
Prognosis
Despite the advanced age and comorbidities of affected patients, prognosis is relatively favorable: