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Cocos Gram-positivos

Aerococcus urinae

Gram-positive cocci in tetrads

Identification & Growth

Identification

  • Catalase-negative, alpha-hemolytic, PYR-negative, LAP-positive
  • Frequently mistaken for viridans streptococci or Enterococcus

Growth Conditions

  • Blood agar and CLED agar, 35–37 °C, CO2, 24–48 h; small alpha-hemolytic colonies

Clinical Significance

  • UTI in the elderly and men with outflow obstruction; urosepsis and endocarditis

Intrinsic Resistance

  • Resistant to trimethoprim-sulfamethoxazole in vivo despite an apparent in vitro zone

Bench Alerts

  • Do not dismiss as a contaminant in a monomicrobial urine culture with pyuria
  • MALDI-TOF resolves identification

Clinical Notes

Clinical presentations

  • Causes urinary tract infection, predominantly in elderly patients with structural or functional genitourinary abnormalities.
  • Can progress to bacteremia and, more rarely, infective endocarditis, especially from an untreated urinary source.

Specimens and collection

  • Midstream or catheter urine is the standard specimen, requiring correlation with symptoms to avoid overvaluing asymptomatic colonization.
  • Blood cultures should be obtained in patients with systemic signs of infection to exclude urinary-source bacteremia.
  • Echocardiogram is recommended in confirmed bacteremia, considering this organism's potential to cause endocarditis.

Epidemiology and at-risk populations

  • Predominantly affects elderly men with benign prostatic hyperplasia or other structural urinary tract abnormalities.
  • Frequently underdiagnosed due to incorrect laboratory identification as a streptococcus or staphylococcus of uncertain significance.

Resistance and therapeutic implications

  • Generally susceptible to penicillin and beta-lactams, which form the basis of urinary infection and bacteremia treatment.
  • Intrinsic resistance to trimethoprim-sulfamethoxazole limits its empiric use for urinary infection caused by this organism.
  • Susceptibility testing should be performed on blood isolates due to potential clinical severity and scarcity of resistance data.

Bench and reporting notes

  • Gram-positive cocci in tetrads, catalase-negative, may be mistaken for coagulase-negative staphylococci or viridans streptococci on microscopy.
  • Mass spectrometry (MALDI-TOF) significantly improves identification accuracy compared to conventional biochemical methods.
  • Characteristic honey/caramel-like odor in urine culture may be an additional clue for presumptive identification.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Aerococcus urinae in the lab?

Aerococcus urinae is identified through catalase-negative, alpha-hemolytic, pyr-negative, lap-positive, frequently mistaken for viridans streptococci or enterococcus.

What are the intrinsic resistances of Aerococcus urinae?

This organism is naturally resistant to resistant to trimethoprim-sulfamethoxazole in vivo despite an apparent in vitro zone. These drugs should not be reported as susceptible.

Where is Aerococcus urinae commonly found?

It is typically associated with uti in the elderly and men with outflow obstruction; urosepsis and endocarditis.

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