Abstract
In a recent study, immunoglobulin G in human plasma was identified as a major inhibitor of diagnostic PCR (W. Abu Al-Soud, L. J. Jönsson, and P. Rådström. J. Clin. Microbiol. 38:345–350, 2000). In this study, two major PCR inhibitors in human blood cells were purified using size exclusion and anion-exchange chromatographic procedures. Based on N-terminal amino acid sequencing and electrophoretic analysis of the purified polypeptides, hemoglobin and lactoferrin were identified as PCR-inhibitor components in erythrocytes and leukocytes, respectively. When different concentrations of hemoglobin or lactoferrin were added to PCR mixtures of 25 μl containing 10 different thermostable DNA polymerases and 1 ng of
Listeria monocytogenes
DNA as template DNA, Ampli
Taq
Gold,
Pwo
, and
Ultma
were inhibited in the presence of ≤1.3 μg of hemoglobin and ≤25 ng of lactoferrin, while
rTth
and
Tli
were found to resist inhibition of at least 100 μg of hemoglobin. In addition, the quantitative effects of seven low-molecular-mass inhibitors, present in blood samples or degradation products of hemoglobin, on real-time DNA synthesis of
rTth
using the LightCycler Instrument were investigated. A reaction system based on a single-stranded poly(dA) template with an oligo(dT) primer annealed to the 3′ end was used. It was found that the addition of 0.25 to 0.1 mg of bile per ml, 2.5 mM CaCl
2
, 0.25 mM EDTA, 5 μM FeCl
3
, and 0.01 IU of heparin per ml reduced the fluorescence to approximately 76, 70, 46, 17, and 51%, respectively. Finally, the effects of nine amplification facilitators were studied in the presence of hemoglobin and lactoferrin. Bovine serum albumin (BSA) was the most efficient amplification facilitator, so that the addition of 0.4% (wt/vol) BSA allowed Ampli
Taq
Gold to amplify DNA in the presence of 20 instead of 1 μg of hemoglobin and 500 instead of 5 ng of lactoferrin. Including 0.02% (wt/vol) gp32, a single-stranded-DNA binding protein, in the reaction mixture of Ampli
Taq
Gold was also found to reduce the inhibitory effects of hemoglobin and lactoferrin.