Development of real-time PCR assays for genotyping of Chlamydia trachomatis

We have developed and validated a nested real-time PCR (NRT-PCR) for the genotyping of Chlamydia trachomatis and used it specifically for the typing of either eight genovars from D to K or three genovars of lymphogranuloma venereum (LGV). The 11 probes used in the NRT-PCR correctly identified the DNA from D to K and LGV reference strains and did not cross-react with the DNA from 26 strains representing the bacterial pathogens and commensals of the oropharynx, genital tract, and rectum. The NRT-PCR had a 95% probability of detection at four genome copies (confidence interval, three to six copies) of C. trachomatis per reaction. One hundred cervical and urethral swab specimens containing C. trachomatis DNA from 63 women and 37 men were used to validate the method. The results from the NRT-PCR and the DNA sequencing of amplicons generated from the omp1 gene showed 100% correlation for these samples. The assay also identified the LGV-II genotype in 24 of 48 rectal swab specimens containing C. trachomatis DNA that were obtained from men having sex with men. The Sexually Transmitted Bacteria Reference Laboratory, London, independently confirmed these results using group-specific LGV real-time PCR and restriction fragment length polymorphism analysis. Compared with the NRT-PCR, non-NRT-PCR was found to be less sensitive: it typed C. trachomatis DNA in only 80% of the genital samples and 90% of the rectal swab samples. This is the first successful demonstration of the use of real-time PCR for the genotype-specific typing of C. trachomatis strains that cause sexually transmitted diseases.