The use of mimics as internal standards to avoid false negatives in diagnostic PCR.

The PCR laboratories may face not only the frequently documented false positive results, but also unexpected false negatives. The latter are mostly due to inhibitory effects of some ingredients and/ or to pipetting errors. In order to reveal the errors, it is advisable to apply standard molecules as indicators of the efficacy of the reactions. In the present paper a rapid and simple method is presented to create internal standards for two test PCR assays. One of the assays detects proviral DNA of bovine leukemia virus (BLV-PCR), the other assay amplifies cDNA of feline infectious peritonitis virus (FIPV-RT-PCR). The internal standard molecules, termed 'mimics', were constructed to have the same primer-binding nucleotide sequences as the viral nucleic acids, but to flank a heterologous DNA fragment of different size. As heterologous DNA, a part of human beta-acin gene was used for the mimic construction. The identical primer-binding nucleotide sequences allowed co-amplification of the viral nucleic acid and the mimic in the same tube, and simultaneously, the size differences allowed easy discrimination between their PCR products. By running a rapid agarose gel electrophoresis after co-amplification, the presence or absence of the mimic PCR products provided proper information on the efficacy of the PCR in each reaction tube. We came to the conclusion that 5 to 20 mimic molecules, co-amplified with the samples, significantly increased the reliability of the diagnostic PCR assays.