Conventional PCR Detection MethodsPCR product detection was traditionally performed by direct visualization of the product using agarose gel electrophoresis with DNA-binding fluorescent dyes such as ethidium bromide. Gel-based methods, although laborious and dependent on subjective result interpretation, are still widely used in diagnostic virology, particularly for PCR-based sequencing and typing (10). In addition, gel-based visualization of PCR product remains an effective way for troubleshooting problems encountered using alternative detection methods. Thus, most diagnostic laboratories maintain gel-based methods to some extent.Enzyme immunoassays, including the enzyme-linked immunosorbent assay (ELISA), provided the first key advancement in PCR detection methodology. Briefly, the PCR-ELISA system used a colorimetric microtiter plate probe-based capture system whereby a 5 biotinylated oligonucleotide probe targeting a DNA sequence internal to the primers was used to capture Lennette's Laboratory Diagnosis of Viral Infections Downloaded from informahealthcare.com by Kainan University on 05/16/15For personal use only.
MOLECULAR AMPLIFICATION METHODS IN DIAGNOSTIC VIROLOGY
21PCR product to streptavidin-coated wells (11). A major advantage of the PCR-ELISA over gel-based techniques is that it is objective, minimizing the potential for interpretation errors. In addition, the technology is particularly suitable for multiplex PCR reactions (discussed below) (12). PCR-ELISA was extensively used in "home-brew" assays as well as in several commercial assays targeting a variety of important viral pathogens, including human immunodeficiency virus (7) and hepatitis C virus (13). However, the PCR-ELISA technology has now been largely superseded by real-time PCR.
Real-Time PCR DetectionThe advent of real-time PCR probably represents the greatest leap in DNA amplification technology since the development of PCR itself, and real-time PCR has been the key advancement in revolutionizing diagnostic virology. Briefly, real-time PCR is achieved through the use of fluorescent detection technology. Fluorescent molecules are added to a PCR reaction mix and interact with the PCR product to produce an increase in fluorescent signal when PCR amplification occurs. Monitoring of the fluorescent output is achieved through real-time PCR instrumentation, which measures the fluorescent signal during or following each thermal cycle. Thus, PCR amplification is monitored in "real-time," providing numerous advantages over conventional detection methods. From a practical perspective, real-time PCR removes the need for a separate detection step, which significantly reduces PCR result turnaround times and decreases staff hands on time. Also, the system is closed (i.e., reactions do not need to be opened for detection), reducing the potential for carryover contamination. The technology also provides an additional key performance characteristic, in that it has an extremely broad dynamic range for virus detection making it highly suitable for viral quan...