Evaluation of the BD Max StaphSR Assay for Detecting Methicillin-Resistant Staphylococcus aureus (MRSA) and Methicillin-Susceptible S. aureus (MSSA) in ESwab-Collected Wound Samples

Staphylococcus aureus is the most common pathogen involved in skin and soft tissue infections, and it is the principal cause of surgical site infections (1–3). Most of the laboratory methods for detecting S. aureus and methicillin-resistant S. aureus (MRSA) from wounds require incubation time and do not support rapid decisions for selection of the most appropriate procedural or therapeutic interventions (4–6). Therefore, wound infections often have negative impacts on patient outcomes— most commonly a delay or deterioration of wound healing potentially leading to sepsis (4, 7). The BD Max StaphSR assay (BD Diagnostic Systems, Québec, Canada) performed on the BD Max system (BD Diagnostic Systems, Sparks, MD) is an FDA-cleared molecular test for detection of S. aureus DNA and MRSA DNA from nasal swab specimens collected from patients at risk of infection due to nasal colonization (8, 9). The BD Max is an automated sample-in and answer-out instrument that combines sample extraction, PCR setup, and real-time PCR on a walkaway platform. This PCR-based test can provide results in approximately 2.5 h. The objective of this study was to evaluate the BD Max StaphSR assay for the detection of S. aureus and MRSA from ESwab (Copan Diagnostics, Murrieta, CA)-collected wound samples and to compare the results to culture, our standard of care procedure. ESwab-collected wound samples are not FDA cleared for use with the BD Max StaphSR assay. A total of 250 ESwab-collected wound samples were included in this study. All samples were tested by two different protocols: the standard of care traditional culture and the BD Max StaphSR assay on the BD Max system. For the standard of care culture, all ESwab-collected wound samples were inoculated onto BBL Trypticase soy agar with 5% sheep blood (blood agar), MacConkey II agar, chocolate II agar, Columbia CNA (colistin-nalidixic acid) agar with 5% sheep blood, and thioglycolate (THIO) broth (BD Diagnostic Systems, Sparks, MD). Swabs were rolled on the first quadrant of each medium, and plates were streaked for isolation using the 4-quadrant technique. Swabs were then wrung out in THIO. Culture plates and THIO were incubated at 35°C and observed for growth at 24 and 48 h. Bacterial colonies were identified by matrixassisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry, the Vitek2 GP identification card, and/or the Pastorex Staph-Plus latex agglutination test (Bio-Rad, Hercules, CA). The BD Max StaphSR assay protocol entailed transferring an aliquot of 200 l from the transport medium of the residual ESwab-collected sample into a BD Max Accepted manuscript posted online 14 June 2017 Citation Silbert S, Gostnell A, Kubasek C, Widen R. 2017. Evaluation of the BD Max StaphSR assay for detecting methicillinresistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in ESwab-collected wound samples. J Clin Microbiol 55:2865–2867. https://doi.org/10 .1128/JCM.00641-17. Editor Betty A. Forbes, Virginia Commonwealth University Medical Center Copyright © 2017 Silbert et al. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license. Address correspondence to Suzane Silbert, [email protected]. LETTER TO THE EDITOR