PCR inhibitors

Many compounds also contained in the PCR template beside the target DNA can interfere with the polymerisation of nucleotides by the Taq or a related polymerase. This may result in false negative results, i.e. no PCR product even though the template is present.

Inhibitors from the purification process

• alcohols like ethanol and 2-propanol (isopropanol) from DNA template precipitation (Qiagen test of sequencing inhibition by Welters et al. 1997)
• organic solvents like phenol from phenol/chloroform purification (PMID 8136148)
• salts like KCl, NaCl from precipitation
• detergents like SDS,.. from membrane lysis (PMID 2223070)

Inhibitors from the source tissue

• components of blood: heme, hemoglobin, lactoferrin, immunoglobin G (IgG)
• liver, digestive tract, feces: bile salts, polysaccharides
• connective tissue, skin: collagen, melanin
• urine: urea

See Rådström et al. 2004 (PMID 14764939) for a review on how to avoid inhibition from tissue components.