The Bcc qPCR NAD assay for the specific rapid quantitative detection of all Bcc species
Huong Thu Duong, Shannon Fullbrook, Kate Reddington, Elizabeth Minogue, Thomas Barry
Abstract
The Bcc qPCR NAD assay presented is an internally controlled duplex assay (incorporating an IAC), targeting a region of the smpB gene for the specific rapid quantitative detection of all Bcc species. This Bcc qPCR NAD assay was validated with equivalence to ISO/TS 12869:2019 with high specificity (100% when tested on an extensive panel of target and non-target microorganisms with no cross-reactivity observed) and high analytical sensitivity (relatively low LOD and LOQ at 3 GE/reaction with ≥90% probability and 20 GE/reaction, respectively). The high performance of the calibration function of the Bcc qPCR NAD assay in terms of accuracy, qPCR efficiency and broad dynamic calibration range (20 GE-107GE/reaction) will allow for the absolute quantification of the starting Bcc DNA concentration in contaminated samples. The incorporation of the IAC into the Bcc qPCR NAD assay ensures the robustness and fidelity of the results generated.
The development and validation of this Bcc qPCR NAD assay has been published in:
Duong HT, Fullbrook S, Reddington K, Minogue E, Barry T. Design, Development and Validation of a Culture-Independent Nucleic Acid Diagnostics Method for the Rapid Detection and Quantification of the Burkholderia cepacia Complex in Water with an Equivalence to ISO/TS 12869:2019. PDA Journal of Pharmaceutical Science and Technology. 2023. doi:10.5731/pdajpst.2021.012728
Steps
Prepare a qPCR master mix (in a DNA-free preparation hood)
Thaw qPCR reagents and samples on the bench, flick to mix and briefly spin down on a tabletop centrifuge.
Prepare a master mix for the number of qPCR reactions, plus negative controls, positive controls (written per reaction):
- 10 µL 2x LightCycler 480 probes master kit
- 3% v/v Dimethyl sulfoxide (DMSO)
- 1 μM Bcc forward primer and 1 μM Bcc reverse primer
- 0.2 μM HEX-labelled Bcc specific hydrolysis probe 1 and 0.2 μM HEX-labelled Bcc specific hydrolysis probe 2
- 0.3 μM IAC forward primer and 0.3 μM IAC reverse primer
- 0.2 μM Cy5-labelled IAC specific hydrolysis probe
- IAC synthetic construct 103 GE/reaction
- The volume is adjusted to 15 µl with the addition of nuclease-free distilled H2O (dH2O).
Note
qPCR oligonucleotide primer and Taqman hydrolysis probe sequences
Gently mix by inversion and briefly centrifuge to collect the liquid at the bottom of the tube.
Set up a qPCR plate (in a PCR template addition hood)
Aliquot 15 µL of master mix to each well of a 96-well PCR white plate.
Add 5 µL of each DNA sample, or 5 µL of gDNA of B. cepacia DSM7288 104GE/reaction (for positive control), or 5 µL of nuclease-free grade water (for negative controls) into appropriate wells of the 96-well PCR white plate.
Seal the plate thoroughly with optical plate sealing film, and centrifuge briefly at low speed to ensure the contents of the wells are at the bottom. Try to remove any bubbles by gently tapping the plate against the bench and spinning again.
The Bcc qPCR NAD assay
Turn on the LightCycler® 480 machine and the attached computer. Login to the computer and the designated software (LightCycler 480 software) using the login details on the computer.
Transfer the plate into the thermal cycler after setting it up appropriately and carry out qPCR reaction at the following conditions:
- 95 °C for 00:10:00
- 95 °C for 00:00:10
- 62 °C for 00:00:30
- Repeat steps 2-3 50cycles (Fluorescent products were detected once every cycle, at the end of the extension phase)
- 40 °C for 00:00:10
Data analysis:
Once qCPR experiment is complete, analyse the result using the LightCycler 480 software to obtain threshold cycle (Ct) signals from each sample.
To determine the quantity of Bcc GE detected in each qPCR reaction, each positive result is quantified from the obtained Ct values and compared to the established Bcc qPCR NAD calibration curve:
y =-3.224 x + 39.46
where x is the log10 of the starting quantity and y is the Ct value.
