Comparison of the BD Max Methicillin-Resistant Staphylococcus aureus (MRSA) Assay and the BD GeneOhm MRSA Achromopeptidase Assay with Direct- and Enriched-Culture Techniques Using Clinical Specimens for Detection of MRSA

Abstract

We evaluated the new, fully automated molecular BD Max methicillin-resistant Staphylococcus aureus (MRSA) assay for detection of methicillin-resistant S. aureus in a low-prevalence (4.1%) setting. Sensitivity, specificity, and positive and negative predictive values were 93.9%, 99.2%, 83.8%, and 99.7%, respectively. The assay reported fewer unresolved results than the BD GeneOhm MRSA ACP assay. M olecular tests for the rapid detection of methicillin-resistantStaphylococcus aureus (MRSA) (10) are used in routine screening programs (6,24,25). Despite intrinsic limitations due to SCCmec variability (4,14,22,23), they are considered an important cornerstone in preventing spread of MRSA in health care facilities (2,7,12). Implementation of MRSA screening programs in hospitals demands greater automation to manage the increased volume of tests (24,25). The BD Max system (Becton, Dickinson Diagnostics, Sparks, MD) is a new, fully automated assay system for commercial and user-developed in vitro molecular diagnostic tests. It combines cell lysis, nucleic acid extraction, PCR setup, amplification, and detection in a single machine, thereby facilitating use of molecular tests. The aim of this study was to evaluate the BD Max MRSA assay, compared with the widely used BD GeneOhm MRSA achromopeptidase (ACP) assay (5,11,17,18,20), using direct and enriched culture as the reference method for detection of MRSA.The study was conducted at the 2,000-bed tertiary care University Hospital Heidelberg from October 2011 to January 2012. Screening swabs (BBL CultureSwab, liquid Stuart; BD) collected from patients admitted to intermediate and intensive care units, from patients admitted from external hospitals, and from surgical patients with wound infections were used. The primary specimen was nasal (91.2%; n ϭ 734) as approved for the test, but perianal (3.7%; n ϭ 30), wound (3.2%; n ϭ 26), and some other swabs were also included. Eight hundred five swabs from 690 individual patients were analyzed by using the BD GeneOhm MRSA ACP assay, BD Max MRSA test, and direct and enrichment culture. Swabs were first placed in 600 l BD GeneOhm MRSA ACP sample buffer and vortexed for 1 min. Ninety microliters was used for the BD GeneOhm MRSA ACP assay run on a SmartCycler II PCR system (Cepheid, Sunnyvale, CA). For the new BD Max MRSA assay, 200 l of the ACP sample buffer was inoculated into the BD Max sample buffer tube. Tubes were loaded into a rack containing the BD Max MRSA unitized reagent strips, extraction and master mix reagents. The BD Max executes the entire test in a fully automated mode. Each day an external positive control (90 l of the hydrated BD GeneOhm MRSA positive control) was included. A negative water control was tested on a weekly basis. Unresolved samples from both molecular tests were reanalyzed once from the sample buffer tube. From the remaining ACP sample buffer, 100 l was removed and directly streaked onto cefoxitin-containing BBL CHROMagar MRSA agar plates (BD), which were inspected after 24 h and 48 h. Moreover, 100 l ...

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

“…More recently, livestock-associated MRSA carrying variant mecC genes further complicated the epidemiology of MRSA by increasing its molecular diversity (5). Microbiology laboratories usually define MRSA phenotypically, but the underlying genetic structures responsible for this phenotype are constantly changing (6)(7)(8), and the molecular assays designed several years back are not necessarily relevant to the epidemiology observed today (9)(10)(11). A recent comparison of culture and a commercial molecular assay performed in a high-prevalence environment showed the molecular assay to be slightly less sensitive than enriched culture using ChromID MRSA agar but also showed that the results were not significantly different, although the molecular assay yielded results in hours instead of days (12).…”

Development of a Real-Time PCR Protocol Requiring Minimal Handling for Detection of Vancomycin-Resistant Enterococci with the Fully Automated BD Max System

“…Running the assay in the type 1 format requires commercial primers/probes as well as the BD MMK (SPC) polymerase and would result in a cost of $31/sample. In addition to the savings for the assay reagents, additional benefit would come from reduced handling times, which should be about 15 min for 8 samples, as published for the respective assays of methicillin-resistant S. aureus (BD GeneOhm MRSA versus BD Max MRSA) (34). A limitation of the study is that it was done at only one center.…”

Duration of Contact Precautions for Acute-Care Settings

“…If positive, the specimen is assigned positive screen status. [99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114] This methodology (called "partial verification") introduces bias in favor of PCR. 115 For MRSA, Yam et al 99 tested 1,246 nares swab specimens with the Lightcycler MRSA Advanced (Roche Molecular Diagnostics, Basel Switzerland), a laboratory developed test (LDT) PCR and, in parallel, cultured all specimens.…”