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Journal of Clinical Microbiology, February 2001, p. 485-493, Vol. 39, No. 2
0095-1137/01/$04.00+0   DOI: 10.1128/JCM.39.2.485-493.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Purification and Characterization of PCR-Inhibitory Components in Blood Cells

Waleed Abu Al-Soud and Peter Rådström*

Applied Microbiology, Center for Chemistry and Chemical Engineering, Lund Institute of Technology, Lund University, SE-221 00 Lund, Sweden

Received 28 February 2000/Returned for modification 24 August 2000/Accepted 23 October 2000

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, AmpliTaq 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 CaCl2, 0.25 mM EDTA, 5 µM FeCl3, 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 AmpliTaq 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 AmpliTaq Gold was also found to reduce the inhibitory effects of hemoglobin and lactoferrin.

* Corresponding author. Mailing address: Applied Microbiology, Center for Chemistry and Chemical Engineering, Lund Institute of Technology, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. Phone: (46)46 222 34 12. Fax: (46)46 222 42 03. E-mail: Peter.Radstrom{at}tmb.lth.se.

Journal of Clinical Microbiology, February 2001, p. 485-493, Vol. 39, No. 2
0095-1137/01/$04.00+0   DOI: 10.1128/JCM.39.2.485-493.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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