Diagnostics
specimens the amount finally represented per PCR reaction was lower for the BD MAX than for the reference assay (see Table 1). Since a maximum of 750 µl of clinical specimen could be used for the BD MAX, it is likely that the sensitivity increases as well. However, this would necessitate reanalysis of inhibition rates, which might also be higher with larger volumes of specimens analysed. Overall, the performance of the BD MAX was very satisfactory.
Another important aspect was the reduction in manual steps when using the BD MAX. Although the turnaround time for 24 specimens was slightly longer (188 minutes) than for the reference assay (174 minutes), the hands-on time was only 48 versus 59 minutes.6 Considering that technicians were more experienced with the reference assay, that the batch-wise preparation of lyophilised reagents (primers, probe) for the reference assay is not included in this calculation and that the time required for BD MAX was continuous, whereas there were breaks when working with the reference assay, this difference becomes even more important.
1. Wittwer CT, Farrar JS, Magic in solution: an introduction and brief history of PCR, In: Kennedy S, Oswald N (eds), PCR Troubleshooting and Optimization, Norfolk: Caister Academic Press, 2011;1–21.
2. Boom R, Sol CJ, Salimans MM, et al., Rapid and simple method for purification of nucleic acids, J Clin Microbiol, 1990;28:495–503.
3. Saiki RK, Gelfand DH, Stoffel S, et al., Primer-directed enzymatic amplification of DNA with a thermostable DNA
Outlook
The longer turnaround time for the simultaneous analysis of 24 specimens may seem somewhat contradictory to the idea of rapid testing with the BD MAX. However, as most of this time is necessary for sequential pipetting steps, the time needed for one–four specimens, numbers rarely exceeded for emergency testing, is reduced to approximately 80 minutes. In combination with the capability of using different cycling conditions for each PCR chamber in the microfluidic cartridge and the availability of six channels in the second-generation instrument, different targets can simultaneously be detected individually or in multiplex assays, making the flexibility even greater.
As of today, only the detection of group B streptococci is available as an IVD test. However, it is planned that additional assays (MRSA, C. difficile toxin gene(s) and others) will become available in the coming months. This, in combination with the flexibility of using laboratory-developed tests, makes the BD MAX a very flexible, reliable, convenient and easy-to-use tool in the molecular diagnostic laboratory. n
polymerase, Science, 1988;239:487–91.
4. Longo MC, Berninger MS, Hartley JL, Use of uracil DNA glycosylase to control carry-over contamination in polymerase chain reactions, Gene, 1990;93:125–8.
5. Holland PM, Abramson RD, Watson R, Gelfand HH, Detection of specific polymerase chain reaction product by utilizing the 5’-3’ exonuclease activity of Thermus aquaticus DNA polymerase, Proc Natl Acad Sci U S A, 1991;88:7276–80.
6. Berlinger L, Sutter-Minder E, Egli K, Altwegg M, Fully automated microfluidic PCR for the detection of Chlamydia trachomatis with the BD MAXTM instrument, Presented at: the 21st European Congress of Clinical Microbiology and Infectious Disease, Abstract P1687, Milan, 7–10 May 2011.
7. Jaton K, Bille J, Greub G, A novel real-time PCR to detect Chlamydia trachomatis in first-void urine or genital swabs, J Med Microbiol, 2006;55:1667–74.
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