Abstract: In order to facilitate analysis of pathogenesis of chlamydial infection, a competitive polymerase chain reaction for the quantitative detection of C.trachomatis was developed. An internal standard(IS) that has the same primer template as the target of the major outer membrance protein gene(ompl) of C.trachomatis was synthesized, cloned and quantified. A standard curve was constructed by co-amplification of known quantities of the cloned ompl target template with IS. Absolute quantitation of the test sample was achieved by co-amplification of constant number of IS with the wild-type target and determining the wild-type target/IS ratio of densitometric value. The number of inclusions in culture and DNA copies in PCR was measured in 11 urogenital specimens. The results show that the DNA copy number per inclusion was approximately 75. This study indicates that competitive PCR provides a reliable and sensitive method of quantitating the number of C.trachomatis in clinical specimens.

Key words: Chlamydia trachomatis, Outer membrane protein gene, Polymerase chain reaction