IVDT_In Vitro Diagnostics Technology

IVD Technology, November/December 2012

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MOLECULAR DIAGNOSTICS Point-of-Care Molecular Diagnostic Testing A target-dependent activation step is combined with isothermal amplifi cation, helicase-dependant amplifi cation, and DNA array-based detection on modifi ed silicon chips to create a visually detectable signal. BY LARRY REA, BRIAN HICKE, WES LINDSEY, MICHAEL MCMAHON, CHARLES OWEN, AND ROBERT JENISON improved patient outcomes. Current culture-based methods for diagnosing HAI are either slow or poorly sensi- tive/specifi c; therefore, broad-spectrum antimicrobial therapy is often initi- ated when there is clinical suspicion of infection. Th is approach may not be eff ective when dealing with inherently resistant organisms and can result in iatrogenic infections. Amplifi cation and detection of nucleic acids (molecu- lar diagnostics) has improved diagnosis for many indications, and sample-to- result technology is of great demand in the clinical diagnostics laboratory, improving workfl ow and effi ciency. Early sample-to-result platforms were highly complex instruments in a centralized laboratory that required specialized technicians to operate, such as the TIGRIS system and ProbeTec systems used for STD pathogen screening and blood screen- ing. To optimize effi ciency and cost, these platforms perform tests in large batches, resulting in slower turnaround time for individual samples. An addi- tional limitation for these approaches is the inability to multiplex, limiting information and increasing cost. Cepheid has pioneered a user-friendly, multiplex-capable instrument, Gen- A ppropriate early treat- ment of hospital-acquired infections (HAI) has been associated with lower treatment costs and ivdtechnology.com eXpert, using real-time PCR technol- ogy. However, limited multiplexing capabilities still do not allow for infor- mation-rich, panel-based testing, and high expense is a burden on hospital laboratory budgets. Nanosphere has addressed multiplexing by coupling target or signal amplifi cation with DNA probe array–based technology in the Verigene SP system; however, its approach requires multiple instru- ments and disposables. Th e complexity and slower speed of either of these approaches make them unacceptable for the point-of-care setting. To address requirements for improved turnaround time, better ease-of-use, and lower cost, Great Basin has developed a molecular diag- nostics approach combining a novel target-dependent activation step with the isothermal amplifi cation method, helicase-dependant amplifi cation (HDA), and DNA array-based detec- tion on modifi ed silicon chips to cre- ate a visually detectable signal. Th is approach is executed in a sample-to- result format using a single low-cost disposable run on an electromechani- cally simple instrument. Recently, a test developed to detect toxigenic Clostridium diffi cile on this platform received 510(k) clearance by FDA. Herein, we describe application of this technology to the detection of staphy- lococcal species and the methicillin- resistance determinant mecA directly from positive blood cultures. bpHDA Amplifi cation Technology PCR technology has demonstrated excellence for amplifi cation of multiple DNA target sequences. However, the technology is limited by the speed of thermal cycling by the instruments. Isothermal amplifi cation methods have appeal due to the simplicity of automa- tion; using a heater at a single tem- perature makes thermal management much easier. Additionally, because the speed of amplifi cation is limited only by the speed of the enzymes, turn- around time may be improved. How- ever, none of the described isothermal methods, which include helicase- IVD TECHNOLOGY | NOVEMBER/DECEMBER 2012 17 DAFT_LION_STUDIO/ISTOCKPHOTO.COM

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