Success Story: Addressing a Key Challenge for PCR-Based Forensic Tests

National Institute of Justice and DNA Polymerase Technologies

Date

April 2016

Overview

Polymerase Chain Reaction (PCR) inhibitors are present in blood, soil, and reagents, and represent a key challenge for PCR-based forensic tests, resulting in false negatives and poor sensitivity of results. Partial Short Tandem Repeat (STR) profiles obtained in the presence of PCR inhibitors appear similar to degraded DNA profiles, which is a major concern for downstream analysis and reporting results obtained from forensic samples. Thermofisher’s AmpliTaq Gold®, a DNA polymerase enzyme that is widely used in forensic DNA testing, is sensitive to PCR inhibitors and can completely inhibit a PCR reaction in the presence of less than 0.1% whole blood. Therefore, current DNA typing protocols must be adapted to achieve a high degree of purity of the evidentiary sample. In general, DNA extraction procedures can be time-consuming or labor-intensive, can cause DNA loss, and may fail to completely remove common inhibitors. Additionally, multiple sample manipulations may increase the risk of cross-contamination. This NIJ funded research examined the effects of PCR inhibitors on the DNA polymerase enzyme from alternative Thermus aquaticus (Taq) mutants and explored an approach to eliminate the need to extract and purify DNA prior to PCR. Removing this step decreases the required time, lowers the cost, and increases the efficiency of forensic DNA typing.

“DNA Polymerase Technologies has done impressive work engineering Taq mutants and in determining the proper combination of PCR enhancer cocktails to assess STR profiles in challenging samples."

- Robert Bever, Ph.D. | Laboratory Director Mitotyping Technologies,
A Division of American International Biotechnology