Application of loop-mediated isothermal amplification technique to rapid and direct detection of methicillin-resistant Staphylococcus aureus (MRSA) in blood cultures

Staphylococcus aureus is the most important pathogen in nosocomial infections, including bloodstream infections. Prompt identification of S. aureus from blood cultures and detection of methicillin resistance are essential in cases of suspected sepsis. A novel nucleic acid amplification technique, loop-mediated isothermal amplification (LAMP), which amplifies DNA under isothermal conditions (63°C) with high specificity, efficiency, and rapidity, was applied to detect methicillin-resistant S. aureus (MRSA) directly from positive blood culture bottles. MRSA-LAMP, which targets the spa gene, encoding S. aureus-specific protein A, and the mecA gene, encoding penicillin-binding protein-2′ for methicillin resistance, could detect MRSA within 2 h after the blood culture signal became positive. The diagnostic values of LAMP, compared to a duplex real-time polymerase chain reaction (Drt-PCR) assay, were 92.3% and 96.2% sensitivity, 100% and 100% specificity, 100% and 100% positive predictive value (PPV), and 96.9% and 98.4% negative predictive value (NPV), respectively. These two methods had almost the same results, but the LAMP method is more cost-effective and provides excellent availability for rapid examination in a hospital clinical laboratory. Therefore, the LAMP assay appears to be a sensitive and reliable new method to diagnose MRSA bloodstream infection for appropriate antibiotic therapy.