Quantification of HEV RNA by Droplet Digital PCR
Florence NicotMichelle CazabatSébastien LhommeOlivier MarionKarine SaunéJulie ChiabrandoMartine DuboisNassim KamarFlorence AbravanelJacques Izopet
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Abstract:
The sensitivity of real-time PCR for hepatitis E virus (HEV) RNA quantification differs greatly among techniques. Standardized tools that measure the real quantity of virus are needed. We assessed the performance of a reverse transcription droplet digital PCR (RT-ddPCR) assay that gives absolute quantities of HEV RNA. Analytical and clinical validation was done on HEV genotypes 1, 3 and 4, and was based on open reading frame (ORF)3 amplification. The within-run and between-run reproducibilities were very good, the analytical sensitivity was 80 HEV RNA international units (IU)/mL and linearities of HEV genotype 1, 3 and 4 were very similar. Clinical validation based on 45 samples of genotype 1, 3 or 4 gave results that correlated well with a validated reverse transcription quantitative PCR (RT-qPCR) assay (Spearman rs = 0.89, p < 0.0001). The RT-ddPCR assay is a sensitive method and could be a promising tool for standardizing HEV RNA quantification in various sample types.Keywords:
Hepatitis E Virus
Environmental DNA (eDNA) has been used to investigate species distributions in aquatic ecosystems. Most of these studies use real-time polymerase chain reaction (PCR) to detect eDNA in water; however, PCR amplification is often inhibited by the presence of organic and inorganic matter. In droplet digital PCR (ddPCR), the sample is partitioned into thousands of nanoliter droplets, and PCR inhibition may be reduced by the detection of the end-point of PCR amplification in each droplet, independent of the amplification efficiency. In addition, real-time PCR reagents can affect PCR amplification and consequently alter detection rates. We compared the effectiveness of ddPCR and real-time PCR using two different PCR reagents for the detection of the eDNA from invasive bluegill sunfish, Lepomis macrochirus, in ponds. We found that ddPCR had higher detection rates of bluegill eDNA in pond water than real-time PCR with either of the PCR reagents, especially at low DNA concentrations. Limits of DNA detection, which were tested by spiking the bluegill DNA to DNA extracts from the ponds containing natural inhibitors, found that ddPCR had higher detection rate than real-time PCR. Our results suggest that ddPCR is more resistant to the presence of PCR inhibitors in field samples than real-time PCR. Thus, ddPCR outperforms real-time PCR methods for detecting eDNA to document species distributions in natural habitats, especially in habitats with high concentrations of PCR inhibitors.
Environmental DNA
In silico PCR
Primer dimer
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Quantitative real-time PCR (qPCR) has been widely implemented for clinical hepatitis B viral load testing, but a lack of standardization and relatively poor precision hinder its usefulness. Droplet digital PCR (ddPCR) is a promising tool that offers high precision and direct quantification. In this study, we compared the ddPCR QX100 platform by Bio-Rad with the CFX384 Touch Real-Time PCR Detection System (Bio-Rad, USA) to detect serial plasmid DNA dilutions of known concentrations as well as HBV DNA extracted from patient serum samples. Both methods showed a high degree of linearity and quantitative correlation. However, ddPCR assays generated more reproducible results and detected lower copy numbers than qPCR assays. Patient sample quantifications by ddPCR and qPCR were highly agreeable based on the Bland-Altman analysis. Collectively, our findings demonstrate that ddPCR offers improved analytical sensitivity and specificity for HBV measurements and is suitable for clinical HBV detection.
Serial dilution
Multiplex
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Human enteric viruses are recognized as the main causes of food- and waterborne diseases worldwide. Sensitive and quantitative detection of human enteric viruses is typically achieved through quantitative RT-PCR (RT-qPCR). A nanofluidic real-time PCR system was used to develop novel high-throughput methods for qualitative molecular detection (RT-qPCR array) and quantification of human pathogenic viruses by digital RT-PCR (RT-dPCR). The performance of high-throughput PCR methods was investigated for detecting 19 human pathogenic viruses and two main process controls used in food virology. The conventional real-time PCR system was compared to the RT-dPCR and RT-qPCR array. Based on the number of genome copies calculated by spectrophotometry, sensitivity was found to be slightly better with RT-qPCR than with RT-dPCR for 14 viruses by a factor range of from 0.3 to 1.6 log10. Conversely, sensitivity was better with RT-dPCR than with RT-qPCR for seven viruses by a factor range of from 0.10 to 1.40 log10. Interestingly, the number of genome copies determined by RT-dPCR was always from 1 to 2 log10 lower than the expected copy number calculated by RT-qPCR standard curve. The sensitivity of the RT-qPCR and RT-qPCR array assays was found to be similar for two viruses, and better with RT-qPCR than with RT-qPCR array for eighteen viruses by a factor range of from 0.7 to 3.0 log10. Conversely, sensitivity was only 0.30 log10 better with the RT-qPCR array than with conventional RT-qPCR assays for norovirus GIV detection. Finally, the RT-qPCR array and RT-dPCR assays were successfully used together to screen clinical samples and quantify pathogenic viruses. Additionally, this method made it possible to identify co-infection in clinical samples. In conclusion, given the rapidity and potential for large numbers of viral targets, this nanofluidic RT-qPCR assay should have a major impact on human pathogenic virus surveillance and outbreak investigations and is likely to be of benefit to public health.
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Objective To reconstruct the initiative procedure of HIV-1 reverse transcription in vitro and establish a methodology of assessing activity of HIV-1 reverse transcriptase (RT) with real-time PCR Methods The tRNALys-3 gene was amplified from genome in healthy individuals through polymerase chain reaction (PCR), and then T7 transcription promoter was added in 5'-terminal of the tRNALys-3. The tRNA[Lys-3 cRNA product was obtained by applying T7 RNA polymerase through a transcription reaction. The 5'-LTR-PBS DNA was also obtained by transcription reaction from the HIV-1 infectious clone and inserted into pGEM-T easy vectors. 5'-LTR-PBS cRNA was obtained by applying SP6 RNA polymerase whose combining site was located in pGEM-T easy vectors. Then the two RNA samples was catalyzed by two kinds of standard reverse transcriptases (SuperScript Ⅲ and HIV-1 standard reverse transcriptase, respectively) and the cDNA was synthesised. The relative activity of RT was determined with the real-time PCR. Results The tRNALys-3 primer and the SP6-5'-LTR-PBS RNA were procured accurately, whose length were 93bp and 872 bp, respectively. After the following serial dilution of Super Script Ⅲ and HIV-1 standard reverse transeriptase:1 : 10, 1: 100, 1:1 000, 1:10 000, each step of reverse transcription process worked successfully. Real-time PCR results showed that Ct values of the two groups were 13.9, 18. 3, 20. 9, 24. 9 and 20. 4, 25. 5, 28. 7, 32. 5 respectively. Conclusion A novel real-time PCR method is developed to assay the RT activity directly through reconstructing the initiation of HIV reproduction, which may be helpful for clinical management, screening of new antiretroviral drugs, and drug resistance test.
Key words:
HIV-1; HIV reverse transcriptase; Polymerase chain reaction
T7 RNA polymerase
Primer (cosmetics)
Transcription
Primer binding site
RNA-Directed DNA Polymerase
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AbstractSince the polymerase chain reaction (PCR) for DNA amplification was first introduced in 1985 (1), the combination of reverse transcription with subsequent PCR amplification of the cDNA (RT-PCR) has been an increasingly utilized technique to analyze gene expression (2,3). In order for this procedure to be reasonably quantitative, however, appropriate controls must be applied to all steps, including the quantitation of the original RNA, the reverse transcription, and the PCR itself. Several investigators have published methods on quantitative RT-PCR that involve varying cDNA input into the PCR (3–7), varying cycle number (3,4,8,9), or the use of a competitive template as an internal standard (10,11). However, only a few of the competitive PCR methods take into account the efficency of the reverse transcription phase of RT-PCR (4,7,11), which may vary from 10-50% (12,13). In the former methods, it would also be necessary to amplify another control gene in parallel (e.g., actin) to control for RNA input and reverse transcription.KeywordsPolymerase Chain ReactionPolymerase Chain Reaction ProductPolymerase Chain Reaction ReactionCompetitive Polymerase Chain ReactionInput cDNAThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Transcription
RNA polymerase II
Primer dimer
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Hepatitis E virus (HEV), the cause of self-limiting acute hepatitis in humans, is widespread and endemic in many parts of the world. The foodborne transmission of HEV has become of concern due to the identification of undercooked pork products as a risk factor for infection. Foodborne enteric viruses are conventionally processed by quantitative RT-PCR (RT-qPCR), which gives sensitive and quantitative detection results. Recently, digital PCR (dPCR) has been described as a novel approach to genome quantification with no need for a standard curve. The performance of microfluidic digital RT-PCR (RT-dPCR) was compared to RT-qPCR when detecting HEV in pig liver products. The sensitivity of the RT-dPCR assay was similar to that of RT-qPCR, and quantitative data obtained by both detection methods were not significantly different for almost all samples. This absolute quantification approach may be useful for standardizing quantification of HEV in food samples and may be extended to quantifying other human pathogens in food samples.
Hepatitis E Virus
Hepatitis E
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Quantitative real-time PCR (QRT-PCR) has been widely implemented for clinical viral load testing, but a lack of standardization and relatively poor precision have hindered its usefulness. Digital PCR offers highly precise, direct quantification without requiring a calibration curve. Performance characteristics of real-time PCR were compared to those of droplet digital PCR (ddPCR) for cytomegalovirus (CMV) load testing. Tenfold serial dilutions of the World Health Organization (WHO) and the National Institute of Standards and Technology (NIST) CMV quantitative standards were tested, together with the AcroMetrix CMV tc panel (Life Technologies, Carlsbad, CA) and 50 human plasma specimens. Each method was evaluated using all three standards for quantitative linearity, lower limit of detection (LOD), and accuracy. Quantitative correlation, mean viral load, and variability were compared. Real-time PCR showed somewhat higher sensitivity than ddPCR (LODs, 3 log(10) versus 4 log(10) copies/ml and IU/ml for NIST and WHO standards, respectively). Both methods showed a high degree of linearity and quantitative correlation for standards (R(2) ≥ 0.98 in each of 6 regression models) and clinical samples (R(2) = 0.93) across their detectable ranges. For higher concentrations, ddPCR showed less variability than QRT-PCR for the WHO standards and AcroMetrix standards (P < 0.05). QRT-PCR showed less variability and greater sensitivity than did ddPCR in clinical samples. Both digital and real-time PCR provide accurate CMV load data over a wide linear dynamic range. Digital PCR may provide an opportunity to reduce the quantitative variability currently seen using real-time PCR, but methods need to be further optimized to match the sensitivity of real-time PCR.
Cytomegalovirus
Cytomegalovirus infections
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