What is Aerococcus urinae?

Aerococcus urinae: An Emerging Urinary Tract Pathogen

Aerococcus urinae is a gram-positive coccus that is an emerging cause of urinary tract infections (UTIs), particularly in elderly patients with underlying urological conditions, and can lead to serious invasive infections including bacteremia and endocarditis with significant morbidity and mortality. 1, 2

Microbiology and Identification

• Aerococcus urinae is a gram-positive coccus that grows in clusters or tetrads and can be easily misidentified as streptococci or staphylococci in routine laboratory testing 2
• The introduction of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has significantly improved the accuracy and speed of identifying Aerococcus species in clinical laboratories 2
• A. urinae is one of seven species in the Aerococcus genus, with A. urinae and A. sanguinicola being the most clinically relevant human pathogens 2

Clinical Significance and Epidemiology

• A. urinae is isolated in a small proportion of urinary specimens but is increasingly recognized as a significant uropathogen 2
• The incidence of A. urinae bacteremia is estimated at approximately three cases per million inhabitants per year 3
• Patient demographics and risk factors include:
  • Predominantly affects elderly patients (median age 72 years) 4
  • Higher prevalence in males, particularly those over 70 years of age 3
  • Strong association with underlying urological conditions (75-79% of cases) 4, 3
  • Other risk factors include chronic kidney disease, heart disease, diabetes mellitus, and dementia 4

Clinical Presentations

• Urinary tract infections: A. urinae can cause both uncomplicated and complicated UTIs 1
• Bacteremia: Often originates from a urinary tract focus, though the organism is rarely isolated from urine cultures in bacteremic patients 3
• Severe sepsis: Approximately 56% of patients with A. urinae bacteremia develop severe sepsis 3
• Infective endocarditis: A serious complication with high mortality (70%) and significant morbidity, including neurological complications 5
• Other reported infections: Balanitis and soft tissue infections 5

Diagnosis

• Urine culture remains the gold standard for identifying A. urinae in UTIs 6
• For accurate identification, MALDI-TOF MS is recommended due to the risk of misidentification with conventional methods 2
• In patients with suspected invasive infection, blood cultures should be obtained 3
• Echocardiography should be considered in patients with A. urinae bacteremia to rule out endocarditis 5

Antimicrobial Susceptibility and Treatment

• A. urinae is generally susceptible to:
  • Penicillin and amoxicillin (100% susceptibility) 4
  • Carbapenems (100% susceptibility) 4
  • Vancomycin (100% susceptibility) 4
  • Nitrofurantoin (95.8% susceptibility) 4
  • Fosfomycin (91.7% susceptibility) 4
• Variable susceptibility to:
  • Fluoroquinolones (ciprofloxacin 83.3%, levofloxacin 79.2%) 4
• For uncomplicated UTIs, nitrofurantoin is an appropriate option 1
• For invasive infections including bacteremia and endocarditis:
  • Beta-lactam antibiotics (particularly penicillin) are the treatment of choice 3
  • For endocarditis, combination therapy with an aminoglycoside should be considered 2
  • Surgical valve replacement may be necessary in cases of endocarditis 5

Clinical Outcomes and Prognosis

• UTIs: Generally good response to appropriate antibiotic therapy 4
• Bacteremia without endocarditis: Favorable prognosis with appropriate treatment 2
• Endocarditis: High mortality rate (70%) and significant morbidity among survivors, including neurovascular complications 5

Emerging Concerns

• Increasing antibiotic resistance has been reported, including ciprofloxacin-resistant isolates 3
• The incidence of A. urinae infections may be underestimated due to misidentification in routine laboratory testing 2
• Prompt and culture-specific treatment is essential to prevent progression to invasive disease 1