Udo Reischl

Institute of Medical Microbiology and Hygiene, University of Regensburg, Franz-Josef-Strauß-Allee 11, 93053 Regensburg, Germany

Received 06/18/96; Accepted 07/19/96; On-line 08/01/96

3. PCR, THE ALL-PURPOSE TOOL IN NUCLEIC ACID-BASED DIAGNOSTICS.

Polymerase chain reaction (PCR), originally introduced by Saiki et al. (7) and subsequently automated by Mullis and Faloona (8), has emerged as a powerful tool in clinical medicine for the exponential in vitro amplification of specific sequences of interest from minute quantities of DNA or RNA and was rapidly applied to the diagnosis of pathogens in clinical material.

This method utilizes the essential portion of the cellular DNA replication machinery (DNA polymerase) in combination with two synthetic oligonucleotides (primers) to reproduce a specific target segment of the DNA in vitro. The reaction is cycled to produce an exponential increase in the target sequence yielding about 10⁶ copies within a few hours (Figure 3). Due to its fundamental principle, PCR has been described as a technique that finds a genetic needle in a haystack and then builds its own haystack of needles.

Because each species has DNA sequences that are unique, it is possible to select PCR-primers that specifically identify infectious agents like bacterial, viral, fungal, and parasitic microorganisms (see (9) for a comprehensive collection of laboratory protocols). Thus, presence of multiple microorganisms can be tested for in one clinical sample and results can be obtained usually within several hours (Figure 3 and Figure 4).

Figure 3: Schematic representation of the polymerase chain reaction (PCR).

Figure 4: Illustration of the exponential nature of the amplification of target by PCR (reproduction with kind permission of Dr. Wehrle, Hoffmann-La Roche AG, Grenzach, Germany).