Development and Validation of a Molecular Beacon Probe–Based Real-Time Polymerase Chain Reaction Assay for Rapid Detection of Methicillin Resistance in Staphylococcus aureus

Abstract

Context.—A rapid, real-time, duplex, fluorescent molecular beacon probe–based polymerase chain reaction (PCR) assay was recently developed for the detection of methicillin-resistant Staphylococcus aureus. Objective.—To describe the development and validation of this unique assay. Design.—Prospective laboratory analysis. Setting.—Urban health region/centralized diagnostic microbiology laboratory. Bacterial Strains.—One hundred eighty-one previously characterized clinical and American Type Culture Collection isolates, including 50 strains each of methicillin-resistant and methicillin-sensitive S aureus, plus 50 strains of coagulase-negative staphylococci and 31 nonstaphylococcal isolates to ensure assay specificity. Intervention.—Assays were performed on purified genomic DNA extracted from growing bacterial colonies. Two sets of oligonucleotide primers were used to specifically amplify the mecA and nuc genes, followed by detection of amplicons using fluorophore-labeled molecular beacon probes. Assays were performed on the Mx4000 Multiplex Quantitative PCR System (Stratagene Inc, La Jolla, Calif). Main Outcome Measures.—(1) Assay sensitivity and specificity, and (2) analytical sensitivity. Results.—The assay demonstrated 100% sensitivity and 100% specificity, and accurately characterized isolates as methicillin-resistant S aureus, methicillin-sensitive S aureus, or methicillin-resistant coagulase-negative staphylococci, with test results available in 2.5 hours. The analytical sensitivity of the assay was determined to be between 6 and 60 genomic equivalents. Conclusions.—This assay is rapid, accurate, easy to perform, and is compatible with other real-time PCR instruments, making it a suitable alternative to conventional PCR methodologies.