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Cocos Gram-positivos

Staphylococcus warneri

Gram-positive cocci in clusters

Identification & Growth

Identification

  • Coagulase-negative, novobiocin-susceptible, urease-positive

Growth Conditions

  • Blood agar, 35–37 °C, 24–48 h

Clinical Significance

  • Blood culture contaminant; rarely endocarditis and shunt infection

Intrinsic Resistance

  • No activity of aztreonam, colistin or nalidixic acid

Bench Alerts

  • Always interpret together with the number of positive bottles and time to positivity

Clinical Notes

Clinical presentations

  • Coagulase-negative staphylococcus associated with catheter-related bacteremia and prosthetic valve endocarditis in immunocompromised hosts.
  • Can cause orthopedic device and ventriculoperitoneal shunt infections.
  • Rarely implicated in postsurgical endophthalmitis.

Specimens and collection

  • Paired blood cultures (peripheral and catheter-drawn) allow differential time-to-positivity to distinguish infection from contamination.
  • Catheter tip should be cultured by Maki's semiquantitative roll-plate method when removed.
  • Multiple positive samples with a matching antibiogram increase the likelihood of clinical significance.

Epidemiology and at-risk populations

  • Colonizes human skin and mucosa, being a frequent blood culture contaminant.
  • Increased risk in patients with central venous catheters and prostheses.
  • Neonates in the ICU are an at-risk population for coagulase-negative staphylococcal bacteremia.

Resistance and therapeutic implications

  • Oxacillin/methicillin resistance is common, mediated by mecA, requiring confirmation with cefoxitin disk diffusion.
  • Methicillin-resistant isolates are reported as resistant to all beta-lactams except ceftaroline.
  • Vancomycin remains the therapeutic mainstay for confirmed invasive infections.

Bench and reporting notes

  • MALDI-TOF species identification is recommended, as manual biochemical tests have poor discrimination among coagulase-negative staphylococci.
  • Correlate with clinical data before treating, given the high potential for specimen contamination.
  • Cefoxitin disk diffusion testing is a reliable surrogate for mecA/mecC detection.

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 Staphylococcus warneri in the lab?

Staphylococcus warneri is identified through coagulase-negative, novobiocin-susceptible, urease-positive.

What are the intrinsic resistances of Staphylococcus warneri?

This organism is naturally resistant to no activity of aztreonam, colistin or nalidixic acid. These drugs should not be reported as susceptible.

Where is Staphylococcus warneri commonly found?

It is typically associated with blood culture contaminant; rarely endocarditis and shunt infection.

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