PCR contamination - (Feb/08/2005 )

Our laboartory working in a diagnosis of Toxoplasma gondii using a Nest-PCR with pecific primers designed in a literature for amplified specific segments of B1 gene.
But my PCR work with contamination in a negative control (my reaction only with water), in that case I am observed a smear and when I amplified the other round of PCR with internal primers we obtained a specif product with the same band that positive control with specif DNA of Toxoplasma gondii. The smear we also obtained in a positive control, but we see the band around 200 bp, that correspond with the PCR product.
I alredy change all stocks including primers, water, Taq and dNTPs, but the smear in a negative control appear.
Other think is that negative control using second internal primers, always we obtained negative, without smear.
Can anyone help me.

Welcome!!

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http://www.protocol-online.org/forums/inde...wtopic=3895&hl=

good luck!