Conventional Real-time RT-PCR Research Articles

One-step and Rapid Identification of SARS-CoV-2 using Real-Time Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP).

SARS-CoV-2 as the cause of novel coronavirus disease (COVID-19) is a member of the family Coronaviridea that has generated an emerging global health concern. Controlling and preventing the spread of the disease requires a simple, portable, and rapid diagnostic method. Today, a standard method for detecting SARS-CoV-2 is quantitative real-time reverse transcription PCR, which is time-consuming and needs an advanced device. The aim of this study was to evaluate a faster and more cost-effective field-based testing method at the point of risk. We utilized a one-step RT-LAMP assay and developed, for the first time, a simple and rapid screening detection assay targeting the Envelope (E) gene, using specific primers. For this, the total RNA was extracted from respiratory samples of COVID-19 infected patients and applied to one-step a RT-LAMP reaction. The LAMP products were visualized using green fluorescence (SYBR Green I). Sensitivity testing was conducted using different concentrations of the designed recombinant plasmid (TA-E) as positive control constructs. Additionally, selectivity testing was performed using the influenza H1N1 genome. Finally, the results were compared using with conventional real time RT-PCR. It was shown that the RT-LAMP assay has a sensitivity of approximately 15 ng for the E gene of SARS-CoV-2 when using extracted total RNA. Additionally, a sensitivity of 112 pg was achieved when using an artificially prepared TA-E plasmid. Accordingly, for the detection of SARS-CoV-2 infection, the RT-LAMP had high sensitivity and specificity and also could be an alternative method for real-time RT-PCR. Overall, this method can be used as a portable, rapid, and easy method for detecting SARS-CoV-2 in the field and clinical laboratories.

Rapid Multiplex RT-PCR for Influenza A and B by Genesoc®, a Microfluidic PCR System.

Rapid antigen tests are widely used to diagnose influenza. However, despite their simplicity and short turnover time, the sensitivity of these tests is relatively low, and molecular tests with greater sensitivity are being sought. In this study, we developed and clinically evaluated a protocol for the rapid multiplex testing of influenza A and B, using a rapid real-time PCR system, GeneSoC®, that is based on microfluidic thermal cycling technology. The specificity of the developed assay was validated using cultured viral strains of influenza A/B, human metapneumovirus, and respiratory syncytial virus. Analytical sensitivity was evaluated using serially diluted RNA synthesized via in vitro transcription and nasopharyngeal swab samples collected from consecutive patients seeking medical attention for a combination of upper respiratory and general symptoms. Cross-validation of GeneSoC® based on comparisons with conventional real-time RT-PCR and rapid antigen tests was performed by parallel testing of influenza-positive clinical specimens. The GeneSoC® assay detected the target sequences of influenza A and B at minimum concentrations of 38 and 65 copies/µL in reaction, respectively. For the analysis of clinical specimens, the positive, negative, and overall agreement between GeneSoC® RT-PCR and a conventional real-time RT-PCR was in all cases 100%, whereas for the comparison between GeneSoC® RT-PCR and the rapid antigen test, the agreements for positive, negative, and overall findings were 100%, 90.9%, and 95.7%, respectively. The mean time for completing GeneSoC® RT-PCR was 16 min 29 s (95% confidence interval, 16 min 18 s to 16 min 39 s). The microfluidic real-time PCR system, GeneSoC®, has an analytical performance comparable to that of conventional real-time RT-PCR with rapid turnover time, and represents a promising alternative to rapid antigen tests for diagnosing influenza A and B.

Comparison of CBNAAT and conventional real time RT PCR for HIV 1 viral load testing

PurposeHIV viral load testing is now recommended for monitoring of anti-retroviral treatment failure in PLHIV. Xpert® HIV-1 Viral Load is a fully automated CB-NAAT. A reduced turnaround time leads to prompt clinical management. Hence the current study was undertaken to compare Xpert® HIV-1 Viral Load with the routinely used conventional real time RT PCR. MethodsThe study was conducted in the Department of Microbiology of a tertiary care medical college after ethics committee approval. 100 HIV positive samples were tested by both CB-NAAT and conventional real time RT PCR for HIV 1 viral load. Results were analyzed using Spearman's correlation co-efficient and Bland Altman plot for agreement. The number of samples with inter assay differences in viral loads exceeding 0.5 log copies/ml was also recorded. The sensitivity, specificity, PPV and NPV as well as the possible misclassification were calculated at the clinically significant value of 1000 copies/ml. Results25 samples in each of the four groups with log 10 value of <3, 3 to <4, 4 to <5 and ≥5 respectively were included. The log difference between the groups varied from 0 to 1.54. CB-NAAT has shown a statistically significant correlation with conventional real time RT PCR by Spearman's rank correlation (R = 0.972) (P < 0.01) and acceptable level of agreement with Bland Altman plot. The sensitivity, specificity, PPV, NPV and diagnostic accuracy was 80%, 100%, 100%, 93.75% and 95% respectively. The overall concordance was 95% with an upward misclassification of 6.25% and downward misclassification of 0%. ConclusionsPoint of care technology with sample in/answer out approach makes it an excellent choice especially in resource constrained and remote settings.

A novel method of multiple nucleic acid detection: Real-time RT-PCR coupled with probe-melting curve analysis

A novel method, real-time reverse transcription PCR (real-time RT-PCR) coupled with probe-melting curve analysis, has been established to detect two kinds of samples within one fluorescence channel. Besides a conventional TaqMan probe, this method employs another specially designed melting-probe with a 5′ terminus modification which meets the same label with the same fluorescent group. By using an asymmetric PCR method, the melting-probe is able to detect an extra sample in the melting stage effectively while it almost has little influence on the amplification detection. Thus, this method allows the availability of united employment of both amplification stage and melting stage for detecting samples in one reaction. The further demonstration by simultaneous detection of human immunodeficiency virus (HIV) and hepatitis C virus (HCV) in one channel as a model system is presented in this essay. The sensitivity of detection by real-time RT-PCR coupled with probe-melting analysis was proved to be equal to that detected by conventional real-time RT-PCR. Because real-time RT-PCR coupled with probe-melting analysis can double the detection throughputs within one fluorescence channel, it is expected to be a good solution for the problem of low-throughput in current real-time PCR.

Genotyping assay for differentiation of wild-type and vaccine viruses in subjects immunized with live attenuated influenza vaccine.

Live attenuated influenza vaccines (LAIVs) are considered as safe and effective tool to control influenza in different age groups, especially in young children. An important part of the LAIV safety evaluation is the detection of vaccine virus replication in the nasopharynx of the vaccinees, with special attention to a potential virus transmission to the unvaccinated close contacts. Conducting LAIV clinical trials in some geographical regions with year-round circulation of influenza viruses warrants the development of robust and reliable tools for differentiating vaccine viruses from wild-type influenza viruses in nasal pharyngeal wash (NPW) specimens of vaccinated subjects. Here we report the development of genotyping assay for the detection of wild-type and vaccine-type influenza virus genes in NPW specimens of young children immunized with Russian-backbone seasonal trivalent LAIV using Sanger sequencing from newly designed universal primers. The new primer set allowed amplification and sequencing of short fragments of viral genes in NPW specimens and appeared to be more sensitive than conventional real-time RT-PCR protocols routinely used for the detection and typing/subtyping of influenza virus in humans. Furthermore, the new assay is capable of defining the origin of wild-type influenza virus through BLAST search with the generated sequences of viral genes fragments.

A strand specific real-time RT-PCR method for the targeted detection of the three species (vRNA, cRNA and mRNA) of infectious salmon anaemia virus (ISAV) replicative RNA

Three species of viral-derived RNA (vRNA, cRNA and mRNA) are produced during an infectious salmon anaemia virus (ISAV) infection. Conventional real-time RT-PCR (RT-qPCR) targeting ISAV segment 8 provides a very sensitive method for the detection of ISAV RNA, however it does not differentiate between these three individual RNA species. In this study, strand-specific tagged primers have been utilised in the RT reaction to specifically produce cDNA corresponding to each of the 3 viral RNA types produced from ISAV segment 8 for the subsequent detection by real-time PCR. The RNA species-specific assay was successfully used to specifically distinguish synthetic T7-produced RNA transcripts representing the 3 species of ISAV RNA at levels up to approximately 10(5)-fold higher than the other types. In addition, the method was applied to investigate the production of segment 8 RNA in time-course tissue culture experiments performed at optimal (15°C), sub-optimal (20°C) and inadequate (25°C) temperatures for replication or in the presence of a chemical inhibitor to vary the RNA populations and investigate its effectiveness. Variation in RNA production was observed between the optimal and sub-optimal temperatures and in the presence of the chemical inhibitor. Production of all RNA species was completely inhibited at 25°C indicating the potential usefulness of the assay as a tool in the understanding of ISAV replication and transcription dynamics.

リアルタイムRT-PCR法によるノロウイルスの定量的迅速検出

We have studied the two assay methods of the 1Step Real-Time RT-PCR and conventional Real-Time RT-PCR (2Step) using ABI PRISM 7000 Sequence Detection System (ABI PRISM 7000) and Thermal Cycler Dice Real Time System (Thermal Cycler Dice) for the detection of Norovirus (NV) genogroups I (G1) and II (GII). Thermal Cycler Dice showed the same performance with the sensitivity and the quantitation compared with ABI PRISM 7000 that the official assay presented for the detection of NV. Both of the 1Step and 2Step Real-Time RT-PCR enabled to get the rapid results about 90 minutes. Excepting the probes with MGB, the primers and probes used in this study were identical with those used in the official assay. Results of field samples using both of the instruments and both of the assays were the same. Hence, these assays are very useful laboratory techniques for the detection of NV from field samples.

Strand-specific real-time RT-PCR for distinguishing influenza vRNA, cRNA, and mRNA

Real-time RT-PCR is used to quantify individual influenza viral RNAs. However, conventional real-time RT-PCR, using strand-specific primers, has been shown to produce not only the anticipated strand-specific products, but also substantial amounts of non-strand-specific products, indicating lack of specificity. Therefore, in this study, a novel strand-specific real-time RT-PCR method was established to quantify the three types of influenza viral RNA (vRNA, cRNA, and mRNA) separately. This method is based on reverse transcription using tagged primers to add a ‘tag’ sequence at the 5′ end and the hot-start method. Real-time PCR using the ‘tag’ portion as the forward primer and a segment-specific reverse primer ensured the specificity for quantifying the three types of RNA. Using this method, specific target RNA was detected at 100–100,000-folds higher level than other types of RNA. This method was also used to evaluate the vRNA, cRNA, and mRNA levels of segments 5 and 6 in MDCK cells infected with influenza A virus at different time point post-infections. The cRNA level was 1/10 to 1/100 lower than that of the vRNA and mRNA. Moreover, different dynamics of vRNA, cRNA, and mRNA synthesis were observed; the copy number of the vRNA gradually increased throughout the infection, the cRNA increased and then plateaued, while the mRNA increased and then decreased. This novel method thus provides data critical for understanding the influenza virus life cycle, including transcription, replication, and genome incorporation into virions.

The quantification of tomato microRNAs response to viral infection by stem-loop real-time RT-PCR

MicroRNAs (miRNAs) are RNA molecules consisting of 20–24 nucleotides that play important roles in regulating plant's gene expression for growth and development, cell viability and stress responses. Viral infection often has a noticeable influence on host gene expression, which may result in a range of developmental abnormalities. To investigate the molecular mechanisms underlying viral infection, miRNA pathway and host gene expression, we report herein the application of the novel miRNAs quantification method in tomato, using a stem-loop reverse transcription followed by SYBR Green PCR assay. For the seven tested miRNAs of Solanum lycopersicum, which are related to the regulation of plant development, hormone response, and their own biogenesis, this quantification method showed high sensitivity, specificity, and wide dynamic range. Precise quantification could be achieved with as little as 0.01 ng of total RNAs for most cases. Additionally, their target mRNAs could be quantified from the same RNA sample simultaneously, by the conventional real-time RT-PCR assay. In comparison with mock inoculation, accumulation levels of the tested miRNAs and target mRNAs were found obviously altered in tomato seedlings, indicating that the miRNA pathway was interrupted by Cucumber mosaic virus and Tomato aspermy virus infection.

Preamplification techniques for real-time RT-PCR analyses of endomyocardial biopsies

BackgroundDue to the limited RNA amounts from endomyocardial biopsies (EMBs) and low expression levels of certain genes, gene expression analyses by conventional real-time RT-PCR are restrained in EMBs. We applied two preamplification techniques, the TaqMan® PreAmp Master Mix (T-PreAmp) and a multiplex preamplification following a sequence specific reverse transcription (SSRT-PreAmp).ResultsT-PreAmp encompassing 92 gene assays with 14 cycles resulted in a mean improvement of 7.24 ± 0.33 Ct values. The coefficients for inter- (1.89 ± 0.48%) and intra-assay variation (0.85 ± 0.45%) were low for all gene assays tested (<4%). The PreAmp uniformity values related to the reference gene CDKN1B for 91 of the investigated gene assays (except for CD56) were -0.38 ± 0.33, without significant differences between self-designed and ABI inventoried Taqman® gene assays. Only two of the tested Taqman® ABI inventoried gene assays (HPRT-ABI and CD56) did not maintain PreAmp uniformity levels between -1.5 and +1.5. In comparison, the SSRT-PreAmp tested on 8 self-designed gene assays yielded higher Ct improvement (9.76 ± 2.45), however was not as robust regarding the maintenance of PreAmp uniformity related to HPRT-CCM (-3.29 ± 2.40; p < 0.0001), and demonstrated comparable intra-assay CVs (1.47 ± 0.74), albeit higher inter-assay CVs (5.38 ± 2.06; p = 0.01). Comparing EMBs from each 10 patients with dilated cardiomyopathy (DCM) and inflammatory cardiomyopathy (DCMi), T-PreAmp real-time RT-PCR analyses revealed differential regulation regarding 27 (30%) of the investigated 90 genes related to both HPRT-CCM and CDKN1B. Ct values of HPRT and CDKN1B did not differ in equal RNA amounts from explanted DCM and donor hearts.ConclusionIn comparison to the SSRT-PreAmp, T-PreAmp enables a relatively simple workflow, and results in a robust PreAmp of multiple target genes (at least 92 gene assays as tested here) by a mean Ct improvement around 7 cycles, and in a lower inter-assay variance in RNA derived from EMBs. Preliminary analyses comparing EMBs from DCM and DCMi patients, revealing differential regulation regarding 30% of the investigated genes, confirm that T-PreAmp is a suitable tool to perform gene expression analyses in EMBs, expanding gene expression investigations with the limited RNA/cDNA amounts derived from EMBs. CDKN1B, in addition to its function as a reference gene for the calculation of PreAmp uniformity, might serve as a suitable housekeeping gene for real-time RT-PCR analyses of myocardial tissues.

Quantitative detection of Citrus tristeza virus in plant tissues and single aphids by real-time RT-PCR

TaqMan real-time reverse transcriptase (RT)-polymerase chain reaction (PCR) using purified RNA targets or coupled to tissue-print and squash procedures was developed to detect and quantify Citrus tristeza virus (CTV) RNA-targets in plant tissues and in single aphids. With this method all CTV isolates tested from different hosts and origins were detected. The sensitivity of conventional real-time RT-PCR was 1,000 times higher than immunocapture (IC)-RT-nested PCR and 106 times higher than enzyme linked immunosorbent assay (ELISA). The quantitation limit ranged from 1.7 × 102 to 1.7 × 109 transcript copies. The estimated number of CTV RNA-targets detected in different organs of a CTV-infected tree ranged from 4.5 × 105 to 6.5 × 108 copies when purified RNA was used as template and from 1.9 × 104 to 3.7 × 106 when tissue-printed material was used. In single squashed aphids the number of copies ranged from 4.73 × 103 to 1.23 × 105. Reliable quantitation of CTV targets present in infected plant material or acquired by single aphid species, was achieved with tissue-print and squash procedures combined with real-time RT-PCR, both of which do not require extraction procedures or nucleic acid purification.

Quantitative investigation of antigen and immune response in nervous and lymphoid tissues of Atlantic halibut ( Hippoglossus hippoglossus) challenged with nodavirus

The present study reports the quantitative analysis of the spatio-temporal development of nodavirus infection and corresponding immune response in juvenile Atlantic halibut ( Hippoglossus hippoglossus) challenged by intramuscular injection of nodavirus. Novel quantitative real-time RT-PCR protocols were applied to evaluate the absolute copy numbers of nodavirus RNA2 (RNA2) and secretory-IgM mRNA (sec-igμ) in the eye, brain, mid/posterior kidney and spleen sampled over a period of 81 days. In the eye and brain, levels of both RNA2 and sec-igμ increased significantly early in the infection. In the spleen and mid/posterior kidney, both RNA2 and sec-igμ were detected but the levels remained unchanged during the experimental period. The levels of RNA2 and sec-igμ in the eye and brain were strongly correlated ( P < 0.0001). Nodavirus antigen was demonstrated by immunohistochemistry (IHC) in the retina of eyes from a relatively few fish from day 34 post challenge (brain not examined), but not at any time in the spleen and anterior kidney. By IHC, IgM+ cells were observed in conjunction with nodavirus positive IHC labelling in the retina. In both the spleen and anterior kidney, the number of IgM+ cells increased from day 3 post challenge. By conventional real-time RT-PCR, RNA2 was only sporadically demonstrated in the posterior intestine, heart and gills. ELISA analysis revealed a nodavirus specific antibody response in serum that was significant from day 18 post challenge. No clinical signs or mortality related to nodavirus infection were observed in the challenged halibut. The results suggest that the nodavirus infection induced a significant antibody response through activation of B-cells in the kidney and spleen, and involved a substantial migration of antibody-secreting cells to infected peripheral tissues.