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

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

	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 discrepant^a AND S. aureus on VITEK 2	Cefoxitin resistant on disk diffusion testing^b	Detection of spa gene	Detection of mecA and the SCCmec-orfX region
Methicillin-susceptible Staphylococcus aureus	DNAse and MSA positive; OR DNAse and MSA discrepant^a AND S. aureus on VITEK 2	Cefoxitin susceptible on disk diffusion testing^b	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 result^b	Absence of spa gene	Presence (resistant) or absence (susceptible) of mecA

DNAse Deoxyribonuclease, MSA Mannitol Salt Agar, CoNS Coagulase-negative staphylococcus
^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
^bCefoxitin category determined by clinical breakpoints outlined in the Clinical and Laboratory Standards Institute M100 document (2016)

ISSN: 1471-2334