Laboratory Evaluation of the BD MAX MRSA Assay

Abstract

A comparison between the BD MAX MRSA and Xpert MRSA assays was performed using 239 nares samples. A 97.9% overall agreement between the two molecular assays was observed. The BD MAX MRSA assay proved to be a reliable alternative for a highly automated system to detect methicillin-resistant Staphylococcus aureus (MRSA) in patient nares samples. Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of community and hospital-acquired infections (1, 2). Screening for MRSA colonization to help identify patients at greater risk for MRSA infection and to allow for initiation of isolation precautions has become standard practice in many institutions (3-7). Molecular amplification methods for MRSA screening of hospitalized patients provides rapid results and have been demonstrated to be more sensitive than culture-based methods (8-15). The BD MAX MRSA assay (BD Diagnostics, Québec, Canada) is a molecular test performed on the BD MAX system (BD Diagnostics, Sparks, MD). 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. The objective of this study was to compare the BD MAX MRSA assay to the only other fully automated walkaway MRSA PCR assay, the Xpert MRSA (Cepheid, Sunnyvale, CA), performed on the GeneXpert instrument (Cepheid).A total of 239 nares samples were collected from August to September 2012 from all patients admitted to any intensive care unit (ICU) at Tampa General Hospital (TGH), using two individually collected traditional swabs (LQ Stuart; BD BBL). One of the swabs was used for the Xpert MRSA assay, and the other was tested by the BD MAX MRSA assay; both assays were performed in parallel on both instruments according to the manufacturer's instructions without the technician having knowledge of the result from either instrument. For the Xpert MRSA assay, samples were placed in the Xpert assay buffer and transferred to the Xpert MRSA cartridge for PCR on the GeneXpert 16 system (Cepheid). For the BD MAX MRSA assay, samples were placed in the BD MAX MRSA sample buffer tube, which was subjected to vortex mixing for 60 s on a multiposition vortex. Sample tubes were placed in the BD MAX system along with the extraction reagent strip and PCR cartridges. The BD MAX MRSA sample buffer supports MRSA viability, which allowed a limited set of samples to be tested by an in-housevalidated mecA and femA PCR, using previously published primers/probes (1), to address discrepant samples.The limit of detection (LOD) of each assay was assessed using a positive-control strain (MRSA, ATCC 33591). Initially, a 0.5-McFarland-standard suspension of the strain was prepared in saline using fresh colonies from a blood agar plate. The suspension was followed by a series of 10-fold dilutions in saline. Five dilutions (1 ϫ 10 3 to 1 ϫ 10 7 CFU/ml) were tested in triplicate by both the Xpert MRSA and the BD MAX MRSA assay. The highest dilution (i.e., lowest concentration) at which all three replicates were positive was cons...

Comparative Evaluation of Two PCR-Based Methods for Detection of Methicillin-Resistant Staphylococcus aureus (MRSA): Xpert MRSA Gen 3 and BD-Max MRSA XT

“…Previous studies have addressed the laboratory efficiency of both platforms using earlier assay versions and have found discrepancies in the turnaround times depending on the number of assays processed and the maximum capacity of the instrument (13). Overall, the hands-on time requirements per sample with the two methods were found to be comparable in our experience.…”

“…However, the sequences of the primers and probes in the two assays are likely distinct, and the extraction processes rely on different principles. The performances of the assays of the previous generations have recently been found to be similar (13), but the release of updated versions warrants a renewed comparison. Moreover, the MRSA clones isolated in Europe and the United States are epidemiologically different and assay performances could be different (14,15).…”

Comparison of time-motion analysis of conventional stool culture and the BD MAX™ Enteric Bacterial Panel (EBP)

“…A number of molecular platforms have been evaluated for specific specimen types, including stool, and potential pathogens in clinical laboratory settings and have been shown to be highly sensitive and specific when compared to conventional methods [ 3 – 5 ]. The BD MAX platform has been evaluated for the detection of MRSA and more recently stool pathogens [ 8 , 9 ]. Recently, several investigators have recognized that beyond scientific validation, these platforms need to be evaluated for their impact on the operations and the time to reportable results in clinical laboratories [ 7 , 10 – 12 ].…”

Using multiplex PCR as a diagnostic tool to detect methicillin resistant Staphylococcus aureus

“…The sensitivity, specificity, and positive and negative predictive values of the assay were found as 84.3%, 99.2%, 88.4%, and 98.9%, respectively. In a report by Widen et al [12], BD MAX and Xpert MRSA assays were compared and good agreement (97.9%) was demonstrated. They concluded that the BD MAX MRSA assay was a reliable alternative automated system for the detection of MRSA from nares samples.…”