Staphylococci, coagulase negative

Paul G. Auwaerter, M.D., John G. Bartlett, M.D.
Staphylococci, coagulase negative is a topic covered in the Johns Hopkins ABX Guide.

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MICROBIOLOGY

  • Coagulase-negative staphylococci (CoNS) are aerobic, Gram-positive coccus, occurring in clusters.
    • Predominantly found on 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:
    • S. lugdunensis:
    • Over forty recognized species of CoNS capable of causing human disease.
  • Many strains with propensity to produce biofilm, allowing for adherence to medical devices.
  • Susceptibility profile for CoNS:
    • Vancomycin (CLSI): MIC cutoffs
      • Sensitive: ≤ 4 mg/L
      • Intermediate: 8-26 mg/L
      • Resistant: ≥ 32 mg/L
      • Note: EUCAST states resistance is MIC > 4 mg/L
      • Vancomycin resistance usually due to cell-wall thickening mechanisms.
    • Oxacillin:
      • Sensitive: ≤ 0.25 mg/L
      • Resistant: > 0.5 mg/L
      • Note: for S. lugdunesis sensitive if ≤ 2 mg/L and resistant for 4 mg/L.
    • Usually resistant of penicillin and typically (80%) to methicillinor oxacillin.
      • 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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MICROBIOLOGY

  • Coagulase-negative staphylococci (CoNS) are aerobic, Gram-positive coccus, occurring in clusters.
    • Predominantly found on 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:
    • S. lugdunensis:
    • Over forty recognized species of CoNS capable of causing human disease.
  • Many strains with propensity to produce biofilm, allowing for adherence to medical devices.
  • Susceptibility profile for CoNS:
    • Vancomycin (CLSI): MIC cutoffs
      • Sensitive: ≤ 4 mg/L
      • Intermediate: 8-26 mg/L
      • Resistant: ≥ 32 mg/L
      • Note: EUCAST states resistance is MIC > 4 mg/L
      • Vancomycin resistance usually due to cell-wall thickening mechanisms.
    • Oxacillin:
      • Sensitive: ≤ 0.25 mg/L
      • Resistant: > 0.5 mg/L
      • Note: for S. lugdunesis sensitive if ≤ 2 mg/L and resistant for 4 mg/L.
    • Usually resistant of penicillin and typically (80%) to methicillinor oxacillin.
      • 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: September 3, 2016