A Novel Primer Probe Set for Detection of SARS-CoV-2 by Sensitive Droplet Digital PCR

AbstractBackgroundThe current increase in the spread of (SARS-CoV-2) critically needs a multitarget diagnostic assays to promote analytical sensitivity to facilitate the public health actions.ObjectiveThe aim of this study was to develop a new primer-probe set targeting N gene of SARS-CoV-2 to improve the sensitivity for detection of COVID-19(Corona Virus Disease 2019)in multiplex rRT-PCR (Reversetranscript Realtime PCR) and ddPCR (Droplet Digital PCR).ResultsWe designed primers/probes set N(LZU3) targeting the N gene of 2019-nCov and proved its sensitivity in both rRT-PCR and ddPCR. When the quantity of template was 105 copies/reaction, the mean Ct value of N(LZU3) was 32.563, the detection rate was 91.7%. If the quantity of template was 52.5 copies/reaction, the mean Ct value of N(LZU3) was 33.835, and the detection rate was 83.3%, which were similar with that of N(CDC) and N(USA). The calculated lower limit of detection (LOD) of the new primer-probe set N(LZU3) used in rRT-PCR was 118 copies/reaction. We also did one-step ddPCR for detection the same serial dilution of RNA template. It shows good linearity for primer/probe sets N(LZU3). The calculated lower limit of detection (LOD) of N(LZU3) was 22.4 copies/reaction, which was 1.12 copies/ul.ConclusionThe novel primer-probe set(LZU3) targeting N gene of SARS-CoV-2 could be both used in rRT-PCR and ddPCR with better sensitivity, furthermore, ddPCR method had higer sensitivity than rRT-PCR, hence it could significantly improve SARS-CoV-2 detection efficiency in low virus load and asymptomatic infection.

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Application of One-Step Reverse Transcription Droplet Digital PCR for Dengue Virus Detection and Quantification in Clinical Specimens

Diagnostics ◽

10.3390/diagnostics11040639 ◽

2021 ◽

Vol 11 (4) ◽

pp. 639

Author(s):

Dumrong Mairiang ◽

Adisak Songjaeng ◽

Prachya Hansuealueang ◽

Yuwares Malila ◽

Paphavee Lertsethtakarn ◽

...

Keyword(s):

Dengue Virus ◽

Lower Limit ◽

Reverse Transcription ◽

Limit Of Detection ◽

Digital Pcr ◽

Droplet Digital Pcr ◽

Clinical Samples ◽

Qrt Pcr ◽

One Step ◽

Detection And Quantification

Detection and quantification of viruses in laboratory and clinical samples are standard assays in dengue virus (DENV) studies. The quantitative reverse transcription polymerase chain reaction (qRT-PCR) is considered to be the standard for DENV detection and quantification due to its high sensitivity. However, qRT-PCR offers only quantification relative to a standard curve and consists of several “in-house” components resulting in interlaboratory variations. We developed and optimized a protocol for applying one-step RT-droplet digital PCR (RT-ddPCR) for DENV detection and quantification. The lower limit of detection (LLOD95) and the lower limit of quantification (LLOQ) for RT-ddPCR were estimated to be 1.851 log10-copies/reaction and 2.337 log10-copies/reaction, respectively. The sensitivity of RT-ddPCR was found to be superior to qRT-PCR (94.87% vs. 90.38%, p = 0.039) while no false positives were detected. Quantification of DENV in clinical samples was independently performed in three laboratories showing interlaboratory variations with biases <0.5 log10-copies/mL. The RT-ddPCR protocol presented here could help harmonize DENV quantification results and improve findings in the field such as identifying a DENV titer threshold correlating with disease severity.

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Rapid Detection and Quantification of Mycobacterium tuberculosis DNA in Paraffinized Samples by Droplet Digital PCR: A Preliminary Study

Frontiers in Microbiology ◽

10.3389/fmicb.2021.727774 ◽

2021 ◽

Vol 12 ◽

Author(s):

Maria Antonello ◽

Rossana Scutari ◽

Calogero Lauricella ◽

Silvia Renica ◽

Valentina Motta ◽

...

Keyword(s):

Limit Of Detection ◽

Bacterial Load ◽

Reference Method ◽

Digital Pcr ◽

Probit Analysis ◽

Droplet Digital Pcr ◽

Smear Microscopy ◽

Analytical Sensitivity ◽

Diagnostic Challenge ◽

Culture Positive

Background: Rapid and reliable diagnosis of tuberculosis (TB) represents a diagnostic challenge in compartmentalized extrapulmonary TB infection because of the small number of mycobacteria (MTB) and the frequent lack of fresh samples to perform culture. Here, we estimate the performances of homemade droplet digital PCR (ddPCR)-based assays against culture in 89 biopsies, for those fresh and formalin-fixed and paraffin-embedded (FFPE) subsamples were available.Methods: MTB diagnosis in fresh subsamples was performed by culture. Fresh subsamples were also analyzed for acid-fast bacilli smear-microscopy (AFB) and Xpert® MTB/RIF (Xpert). MTB examination was repeated in blind in the 89 FFPE subsamples by in-house ddPCR assays targeting the IS6110 and rpoB. Analytical sensitivity of ddPCR assays was evaluated using serial dilution of H37Rv strain. Limit of detection (LOD) was calculated by probit analysis. Results were expressed in copies/106 cells.Results: IS6110 and rpoB ddPCR assays showed a good linear correlation between expected and observed values (R2: 0.9907 and 0.9743, respectively). Probit analyses predicted a LOD of 17 and 40 copies/106 cells of MTB DNA for IS6110 and rpoB, respectively. Of the 89 biopsies, 68 were culture positive and 21 were culture negative. Considering mycobacterial culture as reference method, IS6110 assay yielded positive results in 67/68 culture-positive samples with a median interquartile range (IQR) of 1,680 (550–8,444) copies/106 cells (sensitivity: 98.5%; accuracy: 98.9). These performances were superior to those reported by the rpoB assay in FFPE subsamples (sensitivity: 66.20%; accuracy: 74.1) and even superior to those reported by Xpert and AFB in fresh subsamples (sensitivity: 79.4 and 33.8%, respectively; accuracy: 84.3 and 49.4, respectively). When Xpert and AFB results were stratified according to mycobacterial load detected by rpoB and IS6110 ddPCR, bacterial load was lower in Xpert and AFB negative with respect to Xpert and AFB-positive samples (p = 0.003 and 0.01 for rpoB and p = 0.01 and 0.11 for IS6110), confirming the poor sensitivity of these methods in paucibacillary disease.Conclusion: ddPCR provides highly sensitive, accurate, and rapid MTB diagnosis in FFPE samples, as defined by the high concordance between IS6110 assay and culture results. This approach can be safely introduced in clinical routine to accelerate MTB diagnosis mainly when culture results remain unavailable.

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Clinical Validation of a Quantitative HIV-1 DNA Droplet Digital PCR assay: Applications for Detecting Occult HIV-1 Infection and Monitoring Cell-associated HIV-1 Dynamics across Different Subtypes in HIV-1 Prevention and Cure Trials

10.1101/2020.09.29.20200154 ◽

2020 ◽

Author(s):

Laura Powell ◽

Adit Dhummakupt ◽

Lilly Siems ◽

Dolly Singh ◽

Yann Le Duff ◽

...

Keyword(s):

Mononuclear Cells ◽

Limit Of Detection ◽

Single Copy ◽

Digital Pcr ◽

Droplet Digital Pcr ◽

Analytical Sensitivity ◽

Antibody Testing ◽

Viral Reservoirs ◽

Peripheral Blood Mononuclear ◽

Hiv 1

Background: In HIV-1-exposed infants, nucleic acid testing (NAT) is required to diagnose infection since passively transferred maternal antibodies preclude antibody testing. The sensitivity of clinical NAT assays is lowered with infant antiretroviral prophylaxis and, with empiric very early antiretroviral treatment of high-risk infants, thereby impacting early infant diagnosis. Similarly, adult HIV-1 infections acquired under pre-exposure prophylaxis may occur at low levels (occult infection), with undetectable plasma viremia and indeterminate antibody tests, for which HIV-1 DNA testing maybe a useful adjunct. Cell-associated HIV-1 DNA concentrations are also used to monitor HIV-1 persistence in viral reservoirs with relevance to HIV-1 cure therapeutics, particularly in perinatal infections. Methods: The analytical sensitivity and specificity of an HIV-1 DNA droplet digital PCR (ddPCR) assay was determined, across different HIV-1 subtypes, using serial dilutions of a plasmid containing a 160-base pair sequence of the HIV-1 LTR-gag spiked into peripheral blood mononuclear cells (PBMCs), with MOLT-4 cells or PBMCs infected with different HIV-1 subtypes (A, B and C), and U1 cells spiked into PBMCs. Inter- and intra-run variability were used to determine assay precision. Results: The HIV-1 LTR-gag ddPCR assay was reliable and reproducible, and exhibited high analytical specificity with sensitivity to near single copy level, across multiple HIV-1 subtypes, and a limit of detection of 4.09 copies/million PBMCs. Conclusions. This assay has applications for detecting occult HIV-1-infection that may occur in the setting of combination and long-acting regimens used for HIV-1 prevention, across different HIV-1 subtypes, in both infants and adults, and in HIV-1 cure interventions, particularly with perinatal infections.

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Development and Clinical Validation of a Droplet Digital PCR Method for Detection of Acinetobacter baumannii and Klebsiella pneumonia in Patients with Suspected Bloodstream Infections

10.22541/au.162337143.35366523/v1 ◽

2021 ◽

Author(s):

Yang Zheng ◽

Jun Jin ◽

Ziqiang Shao ◽

Jingquan Liu ◽

Run Zhang ◽

...

Keyword(s):

Blood Culture ◽

Acinetobacter Baumannii ◽

Limit Of Detection ◽

Early Stage ◽

Bloodstream Infections ◽

Digital Pcr ◽

Droplet Digital Pcr ◽

Klebsiella Pneumonia ◽

Clinical Validation ◽

Blood Samples

The relatively long turnaround time and low sensitivity of traditional blood culture may delay the effective antibiotic therapy in patients with bloodstream infection (BSI). To reduce the morbidity and mortality of BSI, a rapid and sensitive pathogen detection method is urgently required. Acinetobacter baumannii and Klebsiella pneumonia are two major microorganisms responsible for BSI. Here we reported a novel droplet digital PCR (ddPCR) method that can detect A. baumannii and K. pneumonia in whole blood samples within 4 h, with a specificity of 100% for each strain and limit of detection at 0.93 copies/microliter for A. baumannii and 0.27 copies/microliter for K. pneumonia. Clinical validation in 170 patients with suspected BSIs showed that, compared with blood culture that reported 4 (2.4%) A. baumannii cases and 7 (4.1%) K. pneumonia cases, ddPCR detected 23 (13.5%) A. baumannii cases, 26 (15.3%) K. pneumonia cases, and 4 (2.4%) dual infection cases, including the 11 positive patients reported by blood culture. In addition, the positive patients reported by ddPCR alone (n = 42) had significantly lower serum concentrations of procalcitonin and lactate, SOFA and APACHE II scores, and 28-day mortality than those reported by both blood culture and ddPCR (n = 11), suggesting that patients with less severe manifestations can potentially benefit from the guidance of ddPCR results. In conclusion, our study suggests that ddPCR represents a sensitive and rapid method to identify causal pathogens in blood samples and to guide the treatment decisions in the early stage of BSI.

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Multiple Hotspot Mutations Scanning by Single Droplet Digital PCR

Clinical Chemistry ◽

10.1373/clinchem.2017.272518 ◽

2018 ◽

Vol 64 (2) ◽

pp. 317-328 ◽

Cited By ~ 21

Author(s):

Charles Decraene ◽

Amanda B Silveira ◽

François-Clément Bidard ◽

Audrey Vallée ◽

Marc Michel ◽

...

Keyword(s):

Liquid Biopsy ◽

Limit Of Detection ◽

Clinical Importance ◽

Digital Pcr ◽

Circulating Tumor Dna ◽

Droplet Digital Pcr ◽

Egfr Mutations ◽

Detection Accuracy ◽

Exon 2 ◽

Exon 19

Abstract BACKGROUND Progress in the liquid biopsy field, combined with the development of droplet digital PCR (ddPCR), has enabled noninvasive monitoring of mutations with high detection accuracy. However, current assays detect a restricted number of mutations per reaction. ddPCR is a recognized method for detecting alterations previously characterized in tumor tissues, but its use as a discovery tool when the mutation is unknown a priori remains limited. METHODS We established 2 ddPCR assays detecting all genomic alterations within KRAS exon 2 and EGFR exon 19 mutation hotspots, which are of clinical importance in colorectal and lung cancer, with use of a unique pair of TaqMan® oligoprobes. The KRAS assay scanned for the 7 most common mutations in codons 12/13 but also all other mutations found in that region. The EGFR assay screened for all in-frame deletions of exon 19, which are frequent EGFR-activating events. RESULTS The KRAS and EGFR assays were highly specific and both reached a limit of detection of <0.1% in mutant allele frequency. We further validated their performance on multiple plasma and formalin-fixed and paraffin-embedded tumor samples harboring a panel of different KRAS or EGFR mutations. CONCLUSIONS This method presents the advantage of detecting a higher number of mutations with single-reaction ddPCRs while consuming a minimum of patient sample. This is particularly useful in the context of liquid biopsy because the amount of circulating tumor DNA is often low. This method should be useful as a discovery tool when the tumor tissue is unavailable or to monitor disease during therapy.

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Sensitive detection of porcine circovirus 3 by droplet digital PCR

Journal of Veterinary Diagnostic Investigation ◽

10.1177/1040638719847686 ◽

2019 ◽

Vol 31 (4) ◽

pp. 604-607

Author(s):

Yuqi Liu ◽

Hecheng Meng ◽

Lei Shi ◽

Lili Li

Keyword(s):

Digital Pcr ◽

Droplet Digital Pcr ◽

Porcine Circovirus ◽

Analytical Sensitivity ◽

Swine Industry ◽

Potential Threat ◽

Emerging Virus ◽

Clinical Detection ◽

Porcine Circovirus 3 ◽

High Degree

Porcine circovirus 3 (PCV-3) is a newly emerging virus that poses a potential threat to the swine industry. We developed a sensitive assay utilizing droplet digital PCR (ddPCR) to detect PCV-3. Specificity of the assay was confirmed by the failure of amplification of DNA of other relevant viruses. The detection limit for ddPCR was 1 copy/μL, 10 times greater sensitivity than TaqMan real-time PCR (rtPCR). Both methods showed a high degree of linearity, although TaqMan rtPCR showed less sensitivity than ddPCR for clinical detection. Our findings indicate that ddPCR might offer faster and improved analytical sensitivity for PCV-3 detection.

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Acoustic array biochip combined with allele-specific PCR for multiple cancer mutation analysis in tissue and liquid biopsy

10.1101/2021.09.16.460590 ◽

2021 ◽

Author(s):

Nikoletta Naoumi ◽

Kleita Michaelidou ◽

George Papadakis ◽

Agapi E. Simaiaki ◽

Roman Fernandez ◽

...

Keyword(s):

Cost Effectiveness ◽

Liquid Biopsy ◽

Point Mutations ◽

Digital Pcr ◽

Droplet Digital Pcr ◽

Braf V600e ◽

Analytical Sensitivity ◽

Specific Pcr ◽

Allele Specific ◽

Allele Specific Pcr

Regular screening of cancerous point mutations is of importance to cancer management and treatment selection. Although excellent techniques like next-generation sequencing and droplet digital PCR are available, these are still lacking in speed, simplicity and cost-effectiveness. Here a new approach is presented where allele-specific PCR (AS-PCR) is combined with a novel High Fundamental Frequency Quartz Crystal Microbalance (HFF-QCM) array biosensor for the amplification and detection, respectively, of cancer point mutations. For the proof-of-concept, the method was applied to the screening of the BRAF V600E and KRAS G12D mutations in spiked-in and clinical samples. Regarding the BRAF target, an analytical sensitivity of 0.01%, i.e., detection of 1 mutant copy of genomic DNA in an excess of 104 wild type molecules, was demonstrated; moreover, quantitative results during KRAS detection were obtained when an optimized assay was employed with a sensitivity of 0.05%. The assays were validated using tissue and plasma samples obtained from melanoma, colorectal and lung cancer patients. Results are in full agreement with Sanger sequencing and droplet digital PCR, demonstrating efficient detection of BRAF and KRAS mutations in samples having an allele frequency below 1%. The high sensitivity and technology-readiness level of the methodology, together with the ability for multiple sample analysis (24 array biochip), cost-effectiveness and compatibility with routine work-flow, hold promise for the implementation of this AS-PCR/acoustic methodology in clinical oncology as a tool for tissue and liquid biopsy.

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A single droplet digital PCR for ESR1 activating mutations detection in plasma

10.1101/507608 ◽

2019 ◽

Author(s):

Emmanuelle Jeannot ◽

Lauren Darrigues ◽

Marc Michel ◽

Marc-Henri Stern ◽

Jean-Yves Pierga ◽

...

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Metastatic Breast Cancer ◽

Limit Of Detection ◽

Growth Factor Receptor ◽

Metastatic Breast ◽

Digital Pcr ◽

Droplet Digital Pcr ◽

Plasma Samples ◽

Activating Mutations

AbstractBackgroundActivating mutations in the estrogen receptor 1 (ESR1) gene are recurrent mechanisms of acquired resistance to aromatase inhibitors (AI), and may be the target of other selective estrogen receptor down-regulators. To assess the clinical utility of monitoring ESR1 resistant mutations, a droplet digital PCR (ddPCR)-based assay compatible with body fluids is ideal due to its cost-effectiveness and quick turnaround.MethodsWe designed a multiplex ddPCR, which combines a drop-off assay, targeting the clustered hotspot mutations found in exon 8, with another pair of probes interrogating the E380Q mutation in exon 5. We assessed its sensitivity in vitro using synthetic oligonucleotides, harboring E380Q, L536R, Y537C, Y537N, Y537S or D538G mutations. Validation of the assay was performed on plasma samples from a prospective study and compared to next generation sequencing (NGS) data.ResultsThe multiplex ESR1-ddPCR showed a high sensitivity with a limit of detection ranging from 0.07 to 0.19% in mutant allele frequency depending on the mutation tested. The screening of plasma samples from patients with AI-resistant metastatic breast cancer identified ESR1 mutations in 29% of them with perfect concordance (and higher sensitivity) to NGS data obtained in parallel. Additionally, this test identifies patients harboring polyclonal alterations. Furthermore, the monitoring of ctDNA using this technique during treatment follow-up predicts the radiological response to palbociclib-fulvestrant.ConclusionThe multiplex ESR1-ddPCR detects, in a single reaction, the most frequent ESR1 activating mutations and is compatible with plasma samples. This method is thus suitable for real-time ESR1 mutation monitoring in large cohorts of patients.Statement of translational relevanceExons 5 and 8 mutations in ESR1 are recurrent mechanisms of resistance to aromatase inhibitors (AI) in estrogen receptor (ER)-positive metastatic breast cancer and may be targeted by selective ER down-regulators. We implemented a novel droplet digital PCR, which allows for the detection of the most frequent ESR1 mutations in circulating cell-free DNA. In prospectively collected plasma samples, ESR1 mutations were found in 29% of AI-resistant patients, with excellent concordance and higher sensitivity to next generation sequencing. Moreover, circulating ESR1 mutations appear to be reliable markers for ctDNA monitoring in order to predict treatment response. Ultimately, the short turnaround time, high sensitivity and limited cost of the ESR1-ddPCR are compatible with repeated samplings to detect the onset of resistance to AI before the radiological progression. This opens a window of opportunity to develop new clinical strategies for breast cancer hormone therapy, as tested in an ongoing phase 3 trial.List of abbreviationsAIAromatase InhibitorcfDNACell-free DNActDNACirculating tumor DNAddPCRDroplet digital PCRER+ HER2-MBCER+ HER2-negative Metastatic Breast CancerEREstrogen ReceptorER+Estrogen Receptor positiveLOBLimit of blankLODLimit of detectionMAFMutant Allele FrequencyPBMCPeripheral blood mononuclear cellsPDProgressive diseaseSDStandard deviationToPTime of progressionWTWild typeHuman genesESR1: Estrogen Receptor 1HER2: Human Epidermal Growth Factor Receptor 2EGFR: Epithelial Growth Factor ReceptorKRAS: KRAS proto-oncogene, GTPaseBRAF: B-Raf Proto-Oncogene, Serine/Threonine kinase

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A Droplet Digital PCR Assay to Detect SARS-CoV-2 RNA

10.1101/2020.05.06.20090449 ◽

2020 ◽

Author(s):

Martin J. Romeo ◽

Christian P. DiPaola ◽

Cassidy Mentus ◽

Cynthia D. Timmers

Keyword(s):

Limit Of Detection ◽

Digital Pcr ◽

The United States ◽

Cross Reactivity ◽

Droplet Digital Pcr ◽

Molecular Testing ◽

Guidance Document ◽

Respiratory Pathogens ◽

Limit Of Quantification ◽

United States Food

AbstractWe describe a quantitative droplet digital PCR (ddPCR) assay for detection of SARS-CoV-2 viral ribonucleic acid (RNA) in total RNA extracted from human sputum. This method was validated using the guidance of the United States Food and Drug Administration’s Accelerated Emergency Use Authorization (EUA) Template for SARS-CoV-2 that Causes Coronavirus Disease (COVID-19) Molecular Testing of Respiratory Speciment in CLIA Certified High-Complexity Laboratories. Though our laboratory is not CLIA certified, this method met all criteria specified by the guidance document with a Limit of Detection (LOD) of 0.25 copies/μL in the final ddPCR (at least 19/20 replicates reactive), which we consider to be a Lower Limit of Quantification (LLOQ); inclusivity of all known annotated SARS-CoV-2 genomes; no cross-reactivity with other respiratory pathogens; and reactivity of all contrived positives at or above the LOD.

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