Treatment of Aerococcus urinae UTI
For a urine specimen growing Aerococcus urinae, treat with ampicillin or amoxicillin as first-line therapy, or nitrofurantoin for uncomplicated cystitis, with treatment duration of 7-14 days based on infection severity. 1, 2, 3
Organism Recognition and Clinical Context
- Aerococcus urinae is an emerging uropathogen primarily affecting elderly patients with multimorbidity, chronic urinary retention, or indwelling catheters 1, 3
- This organism has historically been misidentified as streptococci, leading to underrecognition, but modern MALDI-TOF mass spectrometry has improved detection 3
- While most infections are mild UTIs, serious complications including urosepsis and infective endocarditis can occur, particularly in older males with underlying urinary tract conditions 1, 4, 3
First-Line Treatment Options
For uncomplicated cystitis:
- Nitrofurantoin 100 mg orally every 6 hours for 7 days achieves clinical cure in 71% and microbiological cure in 76% of A. urinae UTI cases 2
- Ampicillin or amoxicillin 500 mg orally every 8 hours for 7-14 days is highly effective, as A. urinae demonstrates 100% susceptibility to these agents 1, 5, 3
For complicated UTI or pyelonephritis:
- Ampicillin remains the preferred agent given universal susceptibility 5, 3
- Ciprofloxacin may be considered for pyelonephritis, though resistance rates of approximately 11% exist 2, 5
Alternative and Adjunctive Therapies
- Pivmecillinam achieves success in A. urinae cystitis cases 2
- Nitroxoline demonstrates high activity (MIC50/90 1/2 mg/L) and 97.6% of isolates would be susceptible using EUCAST breakpoints, though clinical validation is needed 5
- Penicillin combined with an aminoglycoside shows synergy and is recommended for serious infections such as endocarditis or urosepsis 4, 3
Critical Treatment Considerations
- Always obtain urine culture with antibiotic susceptibility testing before initiating therapy, as resistance patterns vary and prompt culture-specific treatment prevents clinical progression 1
- A. urinae shows 100% susceptibility to benzylpenicillin, ampicillin, meropenem, rifampicin, nitrofurantoin, and vancomycin 5
- Resistance to ciprofloxacin occurs in 10.9% of isolates, making fluoroquinolones less reliable empirically 5
- A. urinae is resistant to sulphamethoxazole, and trimethoprim sensitivity testing has methodological problems, so avoid trimethoprim-sulfamethoxazole 3
Treatment Duration
- For uncomplicated cystitis: 7 days is appropriate 2
- For complicated UTI or when using parenteral therapy: extend to 14 days based on clinical response 6
- For serious invasive infections (endocarditis, urosepsis): prolonged therapy with combination regimens is necessary 4
Common Pitfalls to Avoid
- Do not dismiss A. urinae as a contaminant or misidentify it as Streptococcus species - this delays appropriate treatment 3
- Avoid empiric fluoroquinolone monotherapy given the 11% resistance rate 5
- Do not use trimethoprim-sulfamethoxazole, as A. urinae is inherently resistant to sulphamethoxazole 3
- Recognize that elderly patients with multimorbidity are at highest risk for invasive disease requiring more aggressive management 1, 3