Final answer:
The specificity of the PCR process for detecting a particular microbe or virus is provided by the use of primers, which are short DNA sequences that match specific parts of the target DNA or RNA.
Step-by-step explanation:
The reagent that makes the Polymerase Chain Reaction (PCR) specific for a particular microbe or virus is the pair of primers used in the process. Primers are short pieces of DNA that are complementary to each end of the target DNA sequence of the microbe or virus. During PCR, these primers bind or anneal to the specific sequences of the target viral DNA, which allows for the amplification of that particular segment of DNA. If the targeted viral DNA is present in the sample, the PCR will result in the amplification of a DNA fragment of a specific size. In the case of RNA viruses, reverse transcriptase PCR (RT-PCR) is used, where the enzyme reverse transcriptase synthesizes cDNA from the RNA template before the PCR amplification.