An automated magnetic extraction system for Chlamydia trachomatis DNA, tested with the Roche COBAS TaqMan detection system

Abstract number: P1546

Foster A.M.E., Hall Z.F.

Objective:Chlamydia trachomatis accounts for more cases of sexually transmitted infection than any other bacterial pathogen. Methods of detection include culture or antigen detection, both now superseded by amplification reactions. This method is advantageous offering superior sensitivity and specificity and is much quicker to perform. The aim of the study was to evaluate the performance of the automated NorDiag BUGS'N BEADS™ STI-fast kit on the NorDiag Bullet instrument using swabs collected and transported in M4RT^® MicroTest Culture Transport System (Remel, Inc) media with the aim to CE IVD the process. The study was carried out at Dumfries and Galloway Royal Infirmary which serves a population of 146,000. In 2007–08, the total number of Chlamydia tests performed in the region was 7202 with a prevalence rate of 8.8%.

Methods: 704 swabs were tested in parallel using two different extraction methods detailed below. The performance of the BUGS'N BEADS™ STI-fast kit on the Bullet system was compared to the nucleic acid extraction using the Roche AMPLICOR^® CT/NG specimen preparation kit on the Tecan Freedom EVO75 instrument. The BUGS'N BEADS™ STI-fast method is based on nucleic acid extraction using magnetic beads that bind to bacteria and are then magnetically removed from the sample matrix allowing for concentration of the sample, as lysis occurs on the captured cells only. This differs from the Roche specimen preparation kit as it uses detergents to release Chlamydial DNA from Chlamydia reticulate bodies in preparation for amplification.

Detection of Chlamydial DNA for both extraction methods was performed with the COBAS^® TaqMan CT test v 2.0 on a COBAS^® TaqMan 48 analyser. Samples with discrepant results from the two methods were reprocessed in duplicate for both methods. A true positive result was then based on two out of three results.

Results: A total of 704 specimens were tested in parallel. The overall prevalence rate based on true disease status was 5.7%. Table 1 shows the overall results of the study including inhibition.

Conclusion: The results of this study demonstrate that the BUGS'N BEADS™ STI-fast kit exhibits excellent sensitivity and specificity values comparable with the Roche system. Inhibition is significantly reduced; therefore decreasing the number of repeat tests resulting in quicker turn around times. Another benefit of the NorDiag system is the automated sample barcode reader which reduces the possibility of transcription error.

Table 1. Overall results