Comparison of the Velogene Rapid MRSA Identification Assay, Denka MRSA-Screen Assay, and BBL Crystal MRSA ID System for rapid identification of methicillin-resistant Staphylococcus aureus Judy Arbique, Kevin Forward, David Haldane, Ross Davidson* Division of Microbiology, Queen Elizabeth II Health Sciences Centre, Room 309, 5788 University Ave, Halifax, Nova Scotia B3H-1V8, Canada Abstract Early detection of methicillin-resistant S.aureus (MRSA) is critical for both the management of infected patients, and the timely institution of appropriate infection control measures. Although detection of the mecA gene by PCR remains the gold standard, this technology is inaccessible for many laboratories. Therefore, we sought to evaluate several new rapid identification systems and compare them to PCR. A total of 71 methicillin-susceptible S. aureus (MSSA), 25 borderline oxacillin-resistant S. aureus (BORSA), and 213 MRSA were selected for study. S.aureus was identified using standard methods. Initial screening was performed on a Mueller-Hinton agar plate with 6 mg/L of oxacillin. MRSA strains were identified using PCR with primers specific for the mecA gene. PCR was used as the reference method. All isolates were tested using the BBL Crystal MRSA ID System (Becton Dickinson Microbiology Systems, Maryland, USA), the MRSA-Screen Assay (Denka Seiken Co., Ltd., Tokyo, Japan), and the Velogene Rapid MRSA Identification Assay (ID Biomedical Corp, Vancouver, BC). With minor modifications, all assays were performed according to manufacturers’ instructions. Overall, the 3 commercial assays performed well. The sensitivity and specificity of the BBL, Denka, and Velogene systems were 99%/100%, 99%/100%, and 96%/100% respectively. The advantages of the phenotypic tests—BBL Crystal Kit and Denka MRSA-Screen Assay include lower cost per test, shelf-life, ease of use, and rapid turn-around times. Advantages of the Velogene Rapid MRSA include ability to perform genotypic high-volume testing without the equipment requirements and technical complexity involved with PCR. Turn-around times ranged from 15 min for the Denka MRSA-Screen Assay, 2 h for the Velogene Rapid MRSA, and 4 h for the BBL Crystal. The BBL Crystal, Denka MRSA-Screen, and Velogene Rapid MRSA identification systems are rapid, easy to perform, and provide accurate identification of MRSA. These rapid kits offer an acceptable alternative for smaller, non-reference, laboratories and reduce the dependency on PCR in larger laboratories for routine confirmation. © 2001 Elsevier Science Inc. All rights reserved. 1. Introduction Methicillin resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial infection and is a serious infec- tion control concern. Traditionally, MRSA are detected by growth after 24 h at 35°C on Mueller-Hinton agar contain- ing 6 mg/L of oxacillin (MHO), (NCCLS, 2000). Problems may be encountered with strains expressing low-level ox- acillin resistance, since MHO screening plates may not distinguish borderline oxacillin-resistant S. aureus (BORSA) strains from true MRSA (NCCLS, 2000). Be- cause of this, additional testing must be performed before confirming isolates as MRSA. Detection of the mecA gene by PCR remains the gold standard; however, this technol- ogy is not available in many laboratories; confirmation may take more than a day; and the technique is relatively expen- sive. Recently, several commercial kits have become available which offer rapid confirmation of suspected MRSA. Two of these kits—the BBL® Crystal™ MRSA ID System (Becton Dickinson Microbiology Systems, Maryland, USA), and the MRSA-Screen™ Assay (Denka Seiken Co., Ltd., Tokyo, Japan) are phenotypic tests. The BBL Crystal kit contains 4 g/mL oxacillin and uses an oxygen-sensitive fluorescent indicator, which in the presence of oxygen is quenched and colorless when viewed with long-wave ultra-violet light. Oxacillin-resistant organisms utilize oxygen in the suspen- sion broth allowing fluorescence to be observed. Oxacillin- susceptible organisms do not consume the available oxygen, and the fluorescent indicator is quenched. The MRSA-Screen utilizes a latex-coated monoclonal antibody to detect penicillin binding protein 2' (PBP2'), a * Corresponding author. Tel.: +1-902-473-5520; fax: +1-902-473- 4432. E-mail address: plmrjd@qe2-hsc.ns.ca (R. Davidson). www.elsevier.com/locate/diagmicrobio Diagnostic Microbiology and Infectious Disease 40 (2001) 5–10 0732-8893/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0732-8893(01)00245-0