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Use of DNA purification kits for polymerase chain reaction testing of Gen-Probe Chlamydia trachomatis PACE 2
1Laboratory and Radiation Services Division, Colorado Department of Public Health and Environment, Denver, USA. beebe@state.co.us
Background And Objectives:
Confirmation testing using nucleic acid amplification has been shown to improve the sensitivity and specificity of screening tests for Chlamydia trachomatis. However, no critical information on the use of these techniques as an adjunct to Gen-Probe hybridization testing, one of the most common screening methods, has been reported to date. We examined the Roche AMPLICOR PCR C. trachomatis Test (Roche Diagnostic Systems, Branchburg, NJ) as a confirmatory test for the Gen-Probe PACE 2 C. trachomatis Test (San Diego, CA). Further, to mitigate the possible effect of interfering compounds in the Gen-Probe PACE 2 transport medium, we tested various DNA purification techniques.
Study Design:
C. trachomatis elementary bodies were used to spike PACE 2 Transport medium, which was serially diluted, then tested by polymerase chain reaction (PCR). Six parallel dilution series were conducted: (1) saline dilutions tested by the Syva Direct Specimen Test, (2) Roche AMPLICOR transport medium dilutions tested by PCR, and (3-6) dilutions in PACE 2 transport medium purified respectively by GENECLEAN II (BIO101, Vista, CA), Puregene (Gentra Systems, Inc., Research Triangle Park, NC), Microcon 100 (Amicon, Inc., Beverly, MA) DNA isolation kits, and no DNA purification, all tested by PCR. The system giving the best results by in vitro endpoint dilution trials was then used to confirm human specimens previously tested by the Gen-Probe method.
Results:
PCR detected C. trachomatis at 11 twofold dilutions greater than PACE 2 and equivalent to detection of single elementary body by Syva Direct Specimen Test. DNA purification of spiked PACE 2 transport medium by the Microcon 100 kit produced the most consistent PCR detection endpoints, equivalent to endpoints of spiked AMPLICOR transport medium. Endpoints with no DNA purification step were variable and lower. Of 78 endocervical specimens negative by PACE 2 and Gen-Probe Probe Competition Assay, 12 (15.3%) were positive by Microcon DNA purification/PCR testing.
Conclusions:
PCR can be used as confirmation method for Gen-Probe PACE 2 testing, but testing must be performed with a DNA purification procedure.