Improvement of short tandem repeat analysis of samples highly contaminated by humic acid

We investigated several methods for obtaining successful short tandem repeat (STR) results from high-humic acid (HA)-content samples. DNA purification efficiency was tested for QIAquick® PCR Purification, QIAamp® DNA Investigator and Prepfiler™ Forensic DNA Extraction kits. HA-removal capacity of Inhibitor Remover and InhibitEX® Tablet was tested. Experiments on overcoming HA effects on STR amplification were conducted using an AmpliTaq Gold® DNA Polymerase and a TaKaRa Ex Taq™ Hot Start Version (Ex Taq HS) with BSA addition. QIAquick kit was most efficient in HA removal and Ex Taq HS showed high resistance to HA. Increasing the amounts of Taq polymerases and BSA addition were shown to be efficient in overcoming PCR inhibition, but BSA addition was superior to the former method. Inhibitor Remover and InhibitEX® Tablet did not positively affect the STR results. This study will help achieve better STR results with high-HA-content samples.