Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Rapid Differentiation of Staphylococcus from Positive Blood Cultures Using The Xpert® MRSA/SA BC Assay (#114)

Rifky Balgahom 1 , Saroja Dhungel 1 , Timothy Gilbey 1 , Sandra Jones 1 2 , Harsha Samarasekara 1 , James M Branley 1 3
  1. Department of Microbiology and Infectious Diseases, NSW Health Pathology, Nepean Hospital, Penrith, NSW
  2. Department of Microbiology, NSW Health Pathology, Wollongong Hospital, Wollongong, NSW
  3. Infectious Diseases and Microbiology, University of Sydney, Penrith, NSW

Sepsis is a life-threatening condition and one of the leading causes of death in hospital patients worldwide. Timely recognition and management of patients is of paramount importance as delays are associated with high morbidity and mortality. This study evaluated the utility of the Cepheid® Xpert® MRSA/SA BC Assay to rapidly differentiate between Staphylococcus aureus, Methicillin-resistant S. aureus (MRSA) from other Gram positive cocci (including Coagulase negative Staphylococcus (CoNS)) from positive blood cultures where Gram positive cocci in clusters were seen in Gram stain.

Positive Blood Cultures in which Gram positive cocci in clusters were seen in Gram stain from March 2016 - July 2018 were included in the study (n=100). Samples were tested using the Xpert® MRSA/SA BC Assay for the spa, mecA and SCCmec genes according to the manufacturer’s instructions and compared to results obtained from in-house mecA/nuc PCR, Vitek 2 Susceptibility testing (bioMérieux) and conventional bacterial culture. Isolates were identified by MALDI-TOF MS (Bruker).

The correct call of S. aureus (23%), MRSA (15%) or S. aureus negative (58%) was obtained from 96% of specimens tested. Three (3) false negative (3%) and one (1) false positive MRSA result (1%) was obtained.

The Xpert® MRSA/SA BC Assay was able to rapidly differentiate between S. aureus and MRSA from other Gram positive cocci in a reliable manner with the potential to significantly decrease morbidity and mortality in septic patients with S. aureus bacteraemia.