Staphylococci, coagulase negative


  • Coagulase-negative staphylococci (CoNS) are aerobic, Gram-positive coccus, occurring in clusters.
    • Predominantly found on the skin and mucous membranes.
    • Heterogeneous group
    • Catalase positive but coagulase negative (S. aureus is coagulase positive).
  • Major pathogens:
    • S. epidermidis: colonies typically small, white-beige (about 1-2 mm in diameter).
    • S. haemolyticus: colonies typically small, golden yellow (about 1-2 mm in diameter).
    • S. lugdunensis: colonies are usually sticky, smooth, glossy, yellow-orange (2-4 mm).
      • Perhaps the most virulent of CoNS; it behaves similarly to S. aureus.
    • Over 40 recognized species of CoNS capable of causing human disease.
      • Others seen on occasion: Staphylococcus auricularis, Staphylococcus capitis, Staphylococcus hominis, Staphylococcus saprophyticus, and Staphylococcus simulans.
  • Many strains with a propensity to produce biofilm, allowing for adherence to medical devices.
  • Susceptibility profile for CoNS. Breakpoints vary by species.
    • Vancomycin (CLSI): MIC cutoffs
      • Sensitive: ≤ 4 mg/L
      • Intermediate: 8-16 mg/L
      • Resistant: ≥ 32 mg/L
      • Note: EUCAST states resistance is MIC > 4 mg/L
    • Oxacillin (CLSI)
      • S. epidermidis sensitive if ≤ 0.25 mg/L and Resistant if ≥ 0.5 mg/L.
      • S. lugdunensis sensitive if ≤ 2 mg/L and resistant if ≥ 4 mg/L.
    • Usually resistant to penicillin and typically (> 80%) to methicillin (oxacillin, nafcillin).
      • mecA gene encodes for low-affinity penicillin-binding protein.
      • Resistance can be heterotypic, so usually like to see multiple isolates determined as susceptible to beta-lactams, as only a minority of isolates typically express resistance phenotypes.
    • Linezolid resistance described but remains rare.

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Last updated: July 4, 2021