Abstract
A quantitative competitive (QC)-PCR was developed to assay the cell number of Toxoplasma gondii (T. gondii), an intracellulary infective protozoan, by estimating copy numbers of specific gene. The truncated surface antigen gene-1 (SAG1) was used as a competitor of the QC-PCR targeting SAG1 of T. gondii. The Determined amount of competitor SAG1 DNA was coamplified with Fukaya strain genomic DNA. QC-PCR products were electrophoresed in an agarose gel and stained with ethidium bromide. The band intensities of QC-PCR products were measured using a gel densitometer. A good relationship was obtained between the cell numbers of T. gondii and the band intensities of QC-PCR products. From 1 to 10000 copies of SAG1 could be quantitated in 2 micro-g genomic DNA (T. gondii was included in carrier DNA). This method is more simple and sensitive than cell counting methods for T. gondii and may be useful for investigating the organ distributions and kinetics of T. gondii infection. Key words:
Toxoplasma; QC-PCR; SAG1.