Real-time PCR for pharmacodynamic studies of Chlamydia trachomatis

Abstract Pharmacodynamic knowledge about Chlamydia trachomatis exposed to antibiotics is hampered due to methodological limitations. We have developed a quantitative real-time PCR method (qRT-PCR) for determination of viable C. trachomatis . The method measures specific RNA transcripts of omp2 ( omcB ) as an expression of viable C. trachomatis . Two clinical isolates (one strain derived from a patient with recurrent symptoms despite doxycycline treatment) were cultured in McCoy cells and exposed to doxycycline at concentrations of 0.0078–64 mg/L. MIC values were evaluated microscopically by immunofluorescence (IF) and by qRT-PCR performed on cDNA prepared from the total RNA. The MIC for two C. trachomatis strains were determined to 0.016 and 0.031 mg/L by both qRT-PCR and IF. The qRT-PCR assay enabled MIC determinations without subjective evaluation, which is a problem when visually evaluating inclusions. The presented qRT-PCR is a suitable method for MIC determination of C. trachomatis . It has the advantage of giving quantitative measurements of chlamydial RNA levels and the method is useful in pharmacodynamic studies of C. trachomatis .