Serum inhibitors for PCR - DNA extraction from serum samples (Jan/14/2004 )

We are working to find a DNA sequence from a bacteria in erum samples but when we try to make a PCR on the sample, there must be a lot of DNA to detect it. Low concentrations are not detected.
Does anyone knows why serum inhibits the PCR reaction?
Is there any protocol to allow the process?

Thanks for your help.

See

Clinical Microbiology & Infection
Volume 7 Issue 3 Page 164 - March 2001
PCR detection of Streptococcus pneumoniae DNA in serum samples for pneumococcal pneumonia diagnosis
J. Domínguez1*, N. Galí1, L. Matas1, P. Pedroso1, S. Blanco1, M. Giménez1, C. Prat1, N. Sopena2, M. Sabrià2 and V. Ausina1

J Clin Microbiol. 1995 December; 33 (12): 3317–3318
PCR detection of cytomegalovirus DNA in serum as a diagnostic test for congenital cytomegalovirus infection.
C T Nelson, A S Istas, M K Wilkerson, and G J Demmler
Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA.

Comparison of several PCR procedures for detection of serum HCV-RNA using different regions of the HCV genome.
Castillo I, Bartolomé J, Quiroga JA, Carreño V.
Department of Gastroenterology, Fundación Jiménez Díaz, Madrid, Spain.
Different methods for the isolation of hepatitis C virus RNA and several sets of primers from the 5' untranslated, core, NS3, NS3/NS4 and NS5 regions of the hepatitis C virus genome were used for the detection of the viral genome by the polymerase chain reaction. Serum samples from 10 patients with chronic hepatitis C and 10 healthy controls were studied. The best method for the RNA extraction was with cold guanidinium isothiocyanate followed by a denaturation step prior to the polymerase chain reaction.

http://www1.qiagen.com/literature/qiagenne..._QNCl_p9_11.pdf

Acta Trop. 1997 May 30;65(3):139-48.
Evaluation of a simple PCR technique for the diagnosis of Trypanosoma vivax infection in the serum of cattle in comparison to parasitological techniques and antigen-enzyme-linked immuno sorbent assay.
Desquesnes M.
CIRAD-EMVT-GUYANE, Institut Pasteur, French Guiana.
Polymerase chain reaction (PCR) with specific oligonucleotides for the amplification of Trypanosoma vivax DNA has been developed by Masiga et al. (1992) to detect the presence of T. vivax DNA in biting flies. The aim of this experiment was to evaluate the efficacy of this technique when applied directly on cattle serum, without DNA purification, to detect infection.