LAB WORK

• Gram +, catalase +, coagulase +

TREATMENT
CONSULT ID FOR ANY STAPH AUREUS BACTEREMIA. PO ANTIBIOTICS ARE INADEQUATE TREATMENT FOR STAPH AUREUS BACTEREMIA AT ANY POINT IN THERAPY. STAPH AUREUS IN A BLOOD CULTURE IS NEVER A CONTAMINANT.

• Vancomycin drug of choice
  • MICs are increasing recently but still within susceptible range (1-2 mcg/mL)
  • If MIC > 2 mcg/mL on susceptibility testing, consider ID consult and these alternatives:
    • Daptomycin
      • Frequently used in skin infections or MRSA bacteremia
      • DO NOT USE IN PNEUMONIA (inactivated by lung surfactant)
    • Linezolid
      • Indicated for MRSA PNA and skin infections
    • Tigecycline
      • Indicated for complicated SSTI, complicated intra-abdominal infections, and CAP
      • DO NOT USE FOR BACTEREMIA (suboptimal blood concentrations)
• Agents for community-acquired MRSA skin infections only
  • Tetracyclines
  • Bactrim
  • Clindamycin

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CLINICAL TIPS & CONTROVERSIES

• Clindamycin Use
  • S. aureus (and other Gram positive organisms) may carry the MLSb phenotype; if present, can lead to inducible resistance to lincosamides (Clindamycin), macrolides, and streptogramins (Synercid)
    • To detect this, labs can do a "D-test"
• Persistent MRSA Bacteremia
  • May be observed even if appropriate antibiotics on board
  • Questionable if connected to increasing vancomycin MICs
  • Ensure proper source control
  • Guidelines recommend alternative treatment in this case, such as:
    • Daptomycin 10 mg/kg IV q24h PLUS (Bactrim, linezolid, or a beta lactam)
    • Daptomycin 10 mg/kg IV q24h PLUS either gentamicin 1 mg/kg IV q8h or rifampin 600 mg IV/PO in single or divided doses
• Vancomycin MIC "Creep" (Increasing MICs During Treatment)
  • May be attributed to variations among testing systems
    • Microscan, BD-Phoenix, E-test associated with higher MICs
    • Vitek 2, Sensititre associated with lower MICs​