Antibiotics Effective Against Aerococcus urinae
Penicillins (ampicillin, amoxicillin) are the first-line antibiotics for Aerococcus urinae infections, with nitrofurantoin being an excellent alternative for uncomplicated urinary tract infections. 1, 2
First-Line Treatment Options
- Penicillins: Aerococcus urinae isolates consistently show low MICs (minimum inhibitory concentrations) to penicillin and amoxicillin, making these antibiotics highly effective first-line options 1
- Nitrofurantoin: Demonstrates good in vitro activity against A. urinae and achieves clinical and microbiological success in 71-76% of urinary tract infections caused by this organism 3, 4
- Pivmecillinam: Effective for A. urinae cystitis based on clinical outcomes 3
For Severe Infections (Bacteremia, Endocarditis)
- Penicillin or ampicillin combined with gentamicin: This combination shows rapid bactericidal activity in time-kill studies and is recommended for serious infections like endocarditis 1, 5
- Vancomycin with gentamicin: Alternative combination for penicillin-allergic patients with severe infections 1
Alternative Options
- Ciprofloxacin: Effective for pyelonephritis caused by A. urinae, though approximately 10.9% of isolates show resistance 3, 4
- Cephalosporins: Cefepime shows good in vitro activity against A. urinae 1
- Vancomycin: Effective alternative for penicillin-allergic patients 1
- Rifampicin: Demonstrates good in vitro activity 1, 4
Treatment Considerations
- Antibiotic susceptibility testing is important due to increasing antibiotic resistance patterns, particularly for fluoroquinolones 2, 4
- Higher doses may be required for severe infections; for example, high-dose ampicillin (18-30g IV daily) or amoxicillin (500mg every 8 hours) may be necessary for adequate treatment 5
- A. urinae vs. A. sanguinicola: Treatment efficacy differs between these species - nitrofurantoin is more effective against A. urinae (76% microbiological cure) than A. sanguinicola (50% microbiological cure) 3
Special Populations
- Elderly patients with multimorbidity: A. urinae infections are more common in older adults with underlying conditions such as chronic urinary retention, indwelling catheters, or urologic cancers 2
- Patients with endocarditis: Combination therapy with penicillin or vancomycin plus gentamicin is strongly recommended due to the high mortality associated with A. urinae endocarditis 1, 5
Common Pitfalls
- Misidentification: A. urinae may be misidentified as alpha-hemolytic streptococci or enterococci in clinical laboratories 2
- Underestimating severity: What appears as a simple UTI can progress to bacteremia or endocarditis, particularly in elderly patients with comorbidities 5
- Monotherapy for severe infections: Time-kill studies show that penicillin or vancomycin alone exhibit slow or no bactericidal activity against A. urinae, highlighting the importance of combination therapy with aminoglycosides for serious infections 1