Treatment of Aerococcus urinae UTI
For uncomplicated cystitis caused by Aerococcus urinae, amoxicillin or amoxicillin-clavulanate (500-875mg twice daily) is the recommended first-line treatment for 7 days, with nitrofurantoin as an effective alternative option. 1, 2
First-Line Antibiotic Selection
For Uncomplicated Cystitis (Lower UTI)
- Amoxicillin or amoxicillin-clavulanate 500-875mg twice daily is the preferred first-line agent, as A. urinae demonstrates 100% susceptibility to ampicillin/amoxicillin and these agents achieve excellent urinary concentrations 3, 4
- Nitrofurantoin is a highly effective alternative, achieving clinical and microbiological cure in 71% and 76% of A. urinae cystitis cases respectively in prospective studies 2
- Fosfomycin 3g single dose can be considered as an alternative option 1
- Nitroxoline demonstrates high activity (MIC50/90 1/2 mg/L) with 97.6% of A. urinae isolates susceptible, though clinical validation is needed 4
For Complicated UTI or Pyelonephritis
- Parenteral ceftriaxone 75 mg/kg every 24 hours or cefotaxime 150 mg/kg per day divided every 6-8 hours should be used for severe infections requiring hospitalization 1
- Ciprofloxacin achieved success in pyelonephritis cases in observational studies, though 10.9% resistance rates have been documented 2, 4
- A. urinae shows 100% susceptibility to penicillin, ampicillin, meropenem, rifampicin, and vancomycin 4
Treatment Duration
- 7 days is the standard duration for uncomplicated cystitis 1
- 7-14 days is recommended for complicated UTI or pyelonephritis, with 14 days considered when upper tract involvement or delayed response occurs 5, 1
- Courses shorter than 7 days are inferior and should be avoided 1
- A 3-day regimen may be considered only in women aged ≤65 years with catheter-associated UTI after catheter removal, though this is not specifically validated for A. urinae 5
Pre-Treatment Considerations
- Always obtain urine culture with susceptibility testing before initiating treatment to confirm diagnosis and guide therapy, as resistance patterns can vary 1, 6
- If an indwelling catheter has been in place for ≥2 weeks and is still indicated, replace it at the onset of treatment to hasten symptom resolution 5
- Remove catheters as soon as clinically appropriate, as catheterization is a major risk factor for aerococcal UTI 7
Special Populations and Severe Infections
For patients with endocarditis or bacteremia (rare but serious complications):
- Penicillin or vancomycin combined with gentamicin demonstrates rapid bactericidal activity, as monotherapy with penicillin or vancomycin shows slow or no bactericidal effect 3
- High-level aminoglycoside resistance has not been documented in A. urinae isolates 3
Critical Pitfalls to Avoid
- Do not treat asymptomatic bacteriuria with A. urinae, as this fosters antimicrobial resistance without clinical benefit 1
- Avoid fluoroquinolone monotherapy if local resistance exceeds 10% or if the patient has recent fluoroquinolone exposure, given documented resistance rates of 10.9% 4
- Do not use inadequate treatment duration (less than 7 days for uncomplicated cases), as this leads to treatment failure 1
- Failing to obtain pre-treatment cultures can lead to inadequate treatment, particularly important given A. urinae's potential to progress to urosepsis in untreated cases 1, 6
Clinical Context
A. urinae predominantly affects older adults (median age 82 years) with multimorbidity, chronic urinary retention, or indwelling catheters 7, 6. While most infections are monomicrobial (73.9%), untreated cases can precipitate into urosepsis, making prompt culture-specific treatment critical 6.