ABSTRACT
The thermostable DNA polymerase is probably the most important target of PCR-inhibitory substances.1 It is well known that the polymerization activity of DNA polymerases varies with temperature, ionic strength, pH, buffer ions, sulfydryl content, and other chemical agents.2 Another reason for the failure of PCR amplification is the status of the nucleic acids. For instance, any large or small molecule that binds to ssDNA or dsDNA may alter the melting temperature (Tm).3 This type of PCR inhibition can be caused by the presence of human immunoglobulin G, making the target nucleic acids unavailable to PCR.4 Other causes of PCR inhibition are chelation of Mg2+ 5 or interference by ions such as Ca2+ which compete with Mg2+ in binding to the DNA polymerase.6 Heme and lactoferrin inhibit PCR through their ability to release iron ions.7 Thus, the PCR inhibitors may act through one or more of the following mechanisms:8 (1) inactivation of the thermostable DNA polymerase, (2) degradation or capture of the nucleic acids, (3) interference with the cell lysis step, and (4) interference one of the reaction components.
