Evaluation of the BD Max StaphSR Assay for Rapid Identification of Staphylococcus aureus and Methicillin-Resistant S. aureus in Positive Blood Culture Broths

Abstract

bWe evaluated the performance of the BD Max StaphSR assay for the direct detection of Staphylococcus aureus from blood culture medium. In a two-center trial, 155 blood cultures from the BD Bactec FX system and 212 from the bioMérieux BacT/Alert system were tested; 170 bottles yielded S. aureus, and all were identified correctly by the BD Max StaphSR assay. The assay required approximately 2.5 h, thus allowing rapid identification of blood cultures flagged positive. The BD Max StaphSR assay (BD, Quebec, Canada) is a fully automated, qualitative, in vitro diagnostic test for the direct detection of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in patients at risk for nasal colonization. The test uses real-time PCR for the amplification of three DNA targets, i.e., SCCmec right-extremity junction (MREJ), thermostable nuclease (nuc), and methicillin resistance (mecA and mecC). Positivity for MREJ and mecA/mecC is required for the result "MRSA," and detection of nuc or MREJ without mecA/mecC is interpreted as "positive for S. aureus." The BD Max StaphSR assay was shown to have excellent sensitivity (96.4%) and specificity (93.6%), compared to combined direct and enriched cultures, for detection of S. aureus from anterior nares samples (1). In this study, we tested the performance of the StaphSR assay with a different sample type, namely, positive blood culture medium with Gram-positive cocci in clusters.Bloodstream infections often result in the need for intensive care and are associated with high mortality rates and large economic burdens (2). S. aureus is one of the main causes of bloodstream infections (3, 4). Rapid identification of positive blood cultures is a prerequisite for timely targeted treatment of patients with sepsis (5-7). Quick differentiation of S. aureus from coagulase-negative Staphylococcus (CoNS) can reduce the costs of patient care and decrease hospitalization times (8). The use of molecular assays for direct detection of S. aureus in blood culture bottles has been shown to allow rapid diagnosis of S. aureus septicemia, which might improve patient treatment (6, 9, 10). The recently introduced BD Max system allows fully automated realtime PCR, but the currently available BD Max StaphSR assay is CE marked and FDA cleared only for use with nasal swabs (11).In a first stage, we tested the use of the StaphSR assay with blood culture bottles (Bactec Plus Aerobic/F or Bactec Plus Anaerobic/F) that had been artificially inoculated with 1,000 CFU of MRSA, methicillin-susceptible S. aureus (MSSA), or methicillinresistant coagulase-negative Staphylococcus (MR-CoNS). After bottles were flagged positive, aliquots from those bottles were tested by inoculating the sample buffer tube (SBT) of the assay.The blood culture bottles were tested again after an additional 18 to 24 h of incubation, to mimic delayed analysis and to ensure that high DNA levels did not result in competition with any of the PCR target amplifications. We tested three volumes, i.e., 15, 50, and 100 l. All spiked blood cultu...

Evaluation of BD MAX Staph SR Assay for Differentiating Between Staphylococcus aureus and Coagulase-Negative Staphylococci and Determining Methicillin Resistance Directly From Positive Blood Cultures

“…In this study, we obtained Ct values from BD and found that the Ct value distribution for the nuc gene was clearly separate, and the highest Ct value among the S. aureus was 25.6 including mixed infections. This is in line with another study where the Ct values for the nuc target were <27 for all MRSA-positive blood cultures [8]; therefore, we selected a Ct value <27 to indicate positivity.…”

Diagnosis of bloodstream infections from positive blood cultures and directly from blood samples: recent developments in molecular approaches

“…The BD Max TM StaphSR Assay (BD Diagnostic Systems, Qu ebec, Canada) is a CE marked and FDA approved, fully automated diagnostic test which was developed for detection of S. aureus and MRSA in patients at risk for nasal colonization [34]. The test is based on a multiplex real-time PCR and differentiates S. aureus and MRSA by detecting the presence of the nuc and mecA/C genes, and the SCCmec-orfX junction within approximately 2.5 hours [34]. Although the BD Max TM StaphSR Assay was designed for rapid screening of nasal swabs, the performance of the test was also analysed for detecting S. aureus and MRSA from positive BCs [34e36].…”

Performance of BD Max StaphSR for Screening of Methicillin-Resistant Staphylococcus aureus Isolates among a Contemporary and Diverse Collection from 146 Institutions Located in Nine U.S. Census Regions: Prevalence of mecA Dropout Mutants

“…However, six out of eight isolates in fact carried the mecA gene, which would provide a corrected specificity rate of 99.8%. Other studies performed in the United States and Europe have reported sensitivity and specificity rates of Ն94.3% and Ն97.7%, respectively (29,30). However, it is important to mention that these studies evaluated the performance of the BD Max StaphSR from nasal swab samples or directly from blood specimens.…”