A new flexible automated sample preparation method based on paramagnetic particles for the isolation of Chlamydiatrachomatis from urine samples, for downstream analysis using three different naat systems

Abstract number: 1134_03_290

Anglès d’Auriac M., Espelund M., Engen T., Jeansson S., Størvold G., Hjelmevoll S., Nordbø S.A., Haugen I.J., Refseth U.H.

Objectives:  

Chlamydiatrachomatis is the leading cause of sexually transmitted disease worldwide. It is important to improve diagnostic methods using non-invasive sample collection to favor increased testing. With the current available methods, swab still prevails over urine sampling mainly due to higher NAAT inhibition and the necessity of centrifugation of urine samples.

Method:  

A method avoiding centrifugation, chlamCAP (Genpoint, Norway), initially developed for C. trachomatis has been automated using a customized Tecan Miniprep 75 robotic system for DNA preparation from urine samples.

A multi-centre study is presented where urine samples were analysed for C. trachomatis using the automated chlamCAP system combined with three different NAAT 1) BDProbeTec™ ET (Becton Dickinson), 2) validated in-house Taqman PCR and 3) Cobas Amplicor (Roche). Evaluation was performed using the results produced in parallel by the on-site reference DNA preparation methods and a third independent method was used to resolve discrepant results. With this new method, bacterial cells are initially adsorbed to uniquely coated paramagnetic particles and magnetically separated from the urine, removing NAAT inhibiting substances. After lysis at RT and washing, the robot transfers purified DNA, resuspended in the appropriate buffer, to the final NAAT recipient.

Results:  

With the BDProbeTec™ ET SDA as downstream analysis system, specificity obtained for both sample preparations was 99.9 %, whereas a sensitivity of 98.8% and 97.6% was obtained for BDProbeTec™ ET and chlamCAP, respectively. No inhibition was observed using the magnetic particles. For the in-house developed Taqman analysis sensitivity was 95% and 98.3% for on-site reference sample preparation and chlamCAP, respectively. For the CobasAmplicor analysis, sensitivity was 93.1 and 98.3% and specificity at 99.7% and 100%, using Cobas Amplicor and chlamCAP procedure for DNA isolation, respectively.

Conclusion:  

The clear improvements brought by this new automated DNA preparation method will help promote the choice of urine as sample material, alleviating the need of a physician for sample collection. Finally, its compatibility towards diverse NAAT and potential for DNA preparation of other STD organisms such as Neisseriagonorrhoeae, Mycoplasmagenitalium and Ureaplasmaurealyticum, enables the development of a universal automated DNA preparation platform suitable for most STD laboratories.