Evaluation of BD Max StaphSR and BD Max MRSA XT Assays Using ESwab-Collected Specimens

Abstract

The BD Max MRSAXT and the BD Max StaphSR assays were validated for the detection of methicillin-resistant Staphylococcus aureus (MRSA) in ESwab samples. In addition, the BD Max StaphSR assay was evaluated for its ability to detect and differentiate S. aureus and MRSA in the same sample. A total of 255 ESwab samples collected from the anterior nares of patients were tested by each of three BD Max assays, including the BD Max MRSA first-generation assay. The results were compared to those of direct and enrichment culture. Additionally, a challenge panel comprising 14 control strains was evaluated to determine the ability of these assays to correctly identify MRSA and also appropriately differentiate S. Staphylococcus aureus is a leading cause of health care-associated infections. Infection due to S. aureus imposes a high and increasing burden on health care resources and increases morbidity and mortality. Nasal carriage of S. aureus has been identified as a risk factor for the development of infections in various settings. This has been studied extensively in surgical patients (general, orthopedic, and thoracic surgery), patients on hemodialysis, patients on continuous ambulatory peritoneal dialysis (CAPD), HIV-infected patients, and patients in intensive care units (1, 2). Methicillin-resistant S. aureus (MRSA) is an important cause of community-acquired and hospital-acquired infections (3, 4). MRSA can colonize the nares, skin, and other body sites, serving as a reservoir for infection and transmission in health care environments (5-7). Screening for MRSA colonization in order to help identify patients at greater risk for MRSA infection and to allow for the initiation of isolation precautions has become standard practice in many institutions (5,6,(8)(9)(10).MRSA screening using molecular amplification methods provides faster results than culture and has been demonstrated to be more sensitive (11-15). However, most of the molecular commercially available rapid tests are based on the detection of a sequence indicating the integration of the staphylococcal cassette chromosome mec element (SCCmec) within the chromosome and do not specifically target the methicillin resistance gene mecA (16). S. aureus isolates with an SCCmec lacking the mecA gene have been described and can be incorrectly identified as MRSA by assays that do not specifically target the mecA gene (17). False-positive results can lead to unnecessary and expensive isolation and treatment of patients. In addition, MRSA strains with the newly discovered methicillin resistance gene mecC account for 3 to 4% of all new MRSA cases in Denmark (18) and cannot be detected by assays that do not detect the mecC gene (19). These false-negative results can lead to uncontrolled transmission of undetected MRSA strains.The BD Max StaphSR and the BD Max MRSAXT assays (BD Diagnostics, Québec, Canada) performed on the BD Max system (BD Diagnostics, Sparks, MD) are next-generation automated qualitative in vitro diagnostic tests able to detect MRSA strains harboring the m...

Multicenter Evaluation of the Xpert MRSA NxG Assay for Detection of Methicillin-Resistant Staphylococcus aureus in Nasal Swabs

“…False-positive detection of MRSA can lead to unnecessary isolation and increased costs. Previous evaluations of the specificity of commercial assays for the molecular detection of MRSA in nasal swabs indicate that most assays exhibit a specificity of Ն95% (22,31,32). The MRSA NxG assay evaluated in this study showed similar performance characteristics, with an overall specificity of 97.2%.…”

Methicillin-Resistant Staphylococcus aureus Harboring mecC Still Eludes Us in East London, United Kingdom

“…Despite the limited reports of mecC in human isolates, a number of commercial S. aureus PCR assays, available in the UK, now include a mecC target (9,14,15). Similarly, various research groups have designed mecC primers for their S. aureus PCR assays, which we also found to be the most appropriate method when selecting a mecC target for our established S. aureus PCR (16)(17)(18).…”

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.…”