A simple modification of PCR thermal profile applied to evade persisting contamination.

The polymerase chain reaction (PCR), one of the most commonly applied methods of diagnostics and molecular biology has a frustrating downside known as the false positive signal or contamination. Several solutions to avoid and to eliminate PCR contaminations have been worked out to date but the implementation of these solutions to laboratory practice may be laborious and time consuming. A simple approach to circumvent the problem of persisting PCR contamination is reported. The principle of this approach lies in shortening the steps of denaturation, annealing, and elongation in the PCR thermal cycle. The modification leads to the radical decline of false positive signals obtained for the no-template controls without affecting the detection of target PCR products. In the model experiments presented here, the signal of negative control was shifted by about ten cycles up above those for the examined samples so that it could be neglected. We do not recommend this solution in PCR diagnostics, where the sensitivity of detection is of the highest priority. However, the approach could be useful to pass by the problem of persisting contamination in quantitative PCR, where the range of quantitation is usually much above the limits of detection.