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Table 1 Laboratory processing result interpretation of positive blood cultures containing Gram positive cocci in clusters

From: Can the Xpert MRSA/SA BC assay be used as an antimicrobial stewardship tool? A prospective assay validation and descriptive impact assessment study in a South African setting

  Culture-based methods Xpert MRSA/SA BC
Species identification Methicillin susceptibility determination Species identification Methicillin susceptibility determination
Methicillin-resistant Staphylococcus aureus DNAse and MSA positive; OR DNAse and MSA discrepanta AND S. aureus on VITEK 2 Cefoxitin resistant on disk diffusion testingb Detection of spa gene Detection of mecA and the SCCmec-orfX region
Methicillin-susceptible Staphylococcus aureus DNAse and MSA positive; OR DNAse and MSA discrepanta AND S. aureus on VITEK 2 Cefoxitin susceptible on disk diffusion testingb Detection of spa gene Absence of mecA
Coagulase-negative staphylococci DNAse and MSA negative; OR DNAse and MSA discrepant AND no agglutination using Pastorex Staph Plus; OR CoNS species on VITEK 2 Cefoxitin disk diffusion testing resultb Absence of spa gene Presence (resistant) or absence (susceptible) of mecA
  1. DNAse Deoxyribonuclease, MSA Mannitol Salt Agar, CoNS Coagulase-negative staphylococcus
  2. aPastorex Staph Plus-tested isolates exhibiting agglutination were all subjected to VITEK 2 confirmation. Isolates with no agglutination were considered coagulase-negative staphylococci, or were subjected to VITEK 2 identification at the discretion of the clinical microbiologist
  3. bCefoxitin category determined by clinical breakpoints outlined in the Clinical and Laboratory Standards Institute M100 document (2016)