Triplex Real-time PCR Research Articles

Development of a triplex real-time PCR assay for detection and differentiation of gene-deleted and wild-type African swine fever virus

African swine fever (ASF) is an infectious disease of domestic and wild pigs, caused by ASF virus (ASFV). In this study, a triplex real-time PCR assay was developed to detect and differentiate the gene-deleted and wild-type ASFV strains. Three pairs of primers and probes were designed to target the conserved region of B646L gene (p72), MGF_360-14L gene (located in the middle of MGF360-505R gene) and CD2v gene, respectively. Gene-deleted (with MGF360-505R and / or CD2v genes deletion) and wild-type ASFV strains were detected specifically and simultaneously by the assay developed without cross-reactions with other nucleic acids of PCV-2, CSFV, PRRSV, FMDV or SVA. The detection limits of the triplex rPCR were 7.9 copies, 9.7 copies, and 9.6 copies of standard plasmid DNA containing B646L gene, MGF_360-14L gene and CD2v gene, respectively. A total of 1215 field samples were tested in parallel by the triplex rPCR and real-time PCR recommended by OIE, and the B646L gene detection results were completely consistent between these two assays. The triplex rPCR assay was successfully developed to identify pigs infected with wild-type ASFV strains or immunized with the ASFV gene-deleted vaccine.

Development and use of a triplex real-time PCR assay for detection of three DNA viruses in psittacine birds.

Aves polyomavirus 1, psittacine beak and feather disease virus, and psittacid herpesvirus 1 are important pathogens of psittacine birds with the potential to cause substantial morbidity and mortality. Using publically available nucleotide sequences, we developed and validated a triplex real-time PCR (rtPCR) assay to rapidly detect these 3 viruses. The assay had high analytical sensitivity, detecting <6 copies of viral DNA per reaction, and 100% analytical specificity, showing no cross-reactivity with 59 other animal pathogens. Archived formalin-fixed, paraffin-embedded tissues from psittacine birds diagnosed at postmortem as infected with each of the viruses as well as virus-negative birds were used to validate the utility of the assay. Birds were selected for the positive cohort if they showed histologic evidence of infection (i.e., characteristic inclusion bodies in tissues); birds in the negative cohort had final diagnoses unrelated to the pathogens of interest. The triplex rtPCR assay confirmed 98% of histopathology-positive cases, and also identified subclinical infections that were not observed by histologic examination, including coinfections. Birds that tested positive only by rtPCR had significantly higher cycle threshold values compared to those with histologic evidence of infection. Positive, negative, and overall percentage agreements as well as the kappa statistic between the results of the assay and histopathology were high, demonstrating the usefulness of the assay as a tool to confirm disease diagnoses, and to improve detection of subclinical infections.

Toxoplasma gondii in vegetables from fields and farm storage facilities in the Czech Republic.

Infection with Toxoplasma gondii has usually been connected with consumption of improperly treated meat. However, contaminated water and products of plant origin have emerged as new sources of infection in the last few years. Here, 292 vegetable samples-carrot, cucumber and lettuce-obtained from nine farms in the Czech Republic were examined using triplex real time PCR targeting two specific T. gondii sequences. Irrigation water and water used for washing of vegetables were also included. Overall, a positivity rate of 9.6% was found in vegetables. The concentration varied between 1.31×100 and 9.00×102 oocysts/g of sample. A significant difference was found between the positivity of vegetables collected directly from fields and that of vegetables collected from farm storage rooms (4.4-8.6% vs 10-24.1%, respectively). All samples of irrigation water and water used to rinse vegetables were negative. Genotyping based on restriction fragment length polymorphism (RFLP) analysis using seven markers revealed the exclusive presence of genotype II.

A simultaneous triplex TaqMan real-time PCR approach for authentication of caprine and bovine meat, milk and cheese

Goat foodstuffs are considered as healthy foods with high nutritional value. This study demonstrated the development and validation of a triplex real-time PCR on the basis of species-specific and species-conservative TaqMan probes for the simultaneous identification of caprine and bovine DNA in meats, milk and cheeses with a prerequisite designed endogenous control. In this research, caprine and bovine meat, milk and cheese were specifically identified via developed primers and probes, and the limits of detection of this methodology were 0.005 and 0.01 ng DNA of milk and cheese from goat, and 0.01 and 0.05 ng DNA of milk and cheese from cow. Taken together, this approach was elaborated to address dairy adulteration issues to eliminate the fraud of economically motivated goat milk and cheese adulteration by adding cow milk.

Development and validation of two triplex real-time PCR systems for the simultaneous detection of six cereal species in processed meat products

Meat protein can be substituted by plant protein in meat products, and cereals are particularly well-suited for this purpose as they are high in protein content and have good bioavailability. The aim of the present work was to develop real-time PCR assays for the detection and quantification of the six most commonly used cereals barley, oat, rye, maize, rice, and wheat in processed meat products. Emulsified sausages were produced with cereal flours (0.0005–0.1%). Additionally, the effect of different post-processing methods (grilling or storage), packaging materials (cans and artificial sausage casings), and cooking temperatures (75 °C, 117 °C, and 121 °C) were investigated. A negative influence on the detectability of DNA was observed with increasing cooking temperature. All other production parameters showed no significant effect. The limit of quantification was as low as 5 ppm of plant protein for all production conditions, which corresponded to 36–58 mg flour per kg of sausage. The validation of the production of reference material was more accurate for the sausages produced at low than at medium temperatures.Overall, the two triplex real-time PCR systems can be applied for specific, sensitive, and simultaneous detection of these six cereal species in meat products. However, the reference material for quantification has to be carefully chosen due to the negative influence of heat treatment on the detectability of DNA.

Real-time PCR assay for detection of Staphylococcus aureus, Panton-Valentine Leucocidin and Methicillin Resistance directly from clinical samples.

Rapid detection of Methicillin Resistant Staphylococcus aureus (MRSA) is an important concern for both treatment and implementation of infection control policies. The present study provides an ‘in house’ real-time PCR assay to detect directly nuc, pvl, and mecA genes. The assay is able to perform identification of MRSA, Methicillin-Sensitive S. aureus, Methicillin-Resistant Coagulase Negative Staphylococci and the Panton-Valentine leukocidin virulence gene from rectal and pharyngeal swab samples in a screening context. We found an analytical sensitivity of this current Triplex PCR assay of 514 CFU/mL. Analytical specificity was tested with different Gram-positive and Gram-negative species and yielded no false-positive PCR signal. The sensitivity and specificity of the Triplex Real Time PCR were both 100% for these targets when compared with the culture and conventional methods. This assay is readily adaptable for routine use in a microbiology laboratory, as it will enable the implementation of timely and properly guided therapy and infection control strategies.

Human DNA degradation assessment and male DNA detection by quantitative-PCR followed by high-resolution melting analysis

We developed a q-PCR technique that simultaneously evaluates the extent of degradation and determines the gender of a human DNA donor. QYDEG HRM is a triplex real-time PCR whose products are analysed by high-resolution melting (HRM). The system produces three amplicons: (1) transducin (beta)-like 1, Y-linked (TBL1Y) (84bp); (2) large-target sequence (DGlt) (244bp); and (3) small-target sequence (DGst) (152bp). After HRM analysis, three melting peaks are detected in male DNA samples and two in female DNA samples. An imbalance between the DGst and DGlt melting peak heights allows for the estimation of the extent of DNA degradation. For sensitivity assessment, triplicate aliquots of 0.0032 to 50ng/μL DNA were tested, denoting good linearity and reproducibility. The results also showed the analysis to be precise and accurate in the DNA range of 0.04–5ng/μL. Diverse types of DNA samples were tested: experimentally heat-degraded DNA; crime scene samples derived from casework and highly degraded samples with partial STR profiles from corpse material and mass disaster events. The results were compared with those obtained from the Plexor® and PowerQuant® commercial kits. Additionally, the quantification results of the QYDEG HRM triplex correlate well with the STR amplification that was subsequently obtained. The method is simple, cost-effective and helpful for determining the DNA integrity and the sex of a sample donor in any field where human DNA quantification is required.

Triplex real-time PCR assay for the detection of Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae directly from clinical specimens without extraction of DNA

This study presents a triplex real-time PCR assay that allows for the direct detection of Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae in one reaction without DNA extraction, with similar sensitivity and specificity to singleplex assays. This approach saves time, specimen volume and reagents while achieving a higher testing throughput.

Generation of a potential koi herpesvirus live vaccine by simultaneous deletion of the viral thymidine kinase and dUTPase genes.

Koi herpesvirus (KHV, Cyprinidherpesvirus 3) causes a fatal disease of koi and common carp. To obtain safe and efficacious live vaccines, we generated deletion mutants of KHV lacking the nonessential genes encoding two enzymes of nucleotide metabolism, thymidine kinase (TK, ORF55) and deoxyuridine-triphosphatase (DUT, ORF123). Since single-deletion mutants based on a KHV isolate from Israel (KHV-I) only exhibited partial attenuation (Fuchs W, Fichtner D, Bergmann SM, Mettenleiter TC. Arch Virol 2011;156 : 1059-1063), a corresponding double mutant was generated and tested in vivo, and shown to be almost avirulent but still protective. To overcome the low in vitro virus titres of KHV-I (≤105 p.f.u. ml-1), single and double TK and DUT deletions were also introduced into a cell culture-adapted KHV strain from Taiwan (KHV-T). The deletions did not affect in vitro virus replication, and all KHV-T mutants exhibited wild-type-like plaque sizes and titres exceeding 107 p.f.u. ml-1, as a prerequisite for economic vaccine production. Compared to wild-type and revertant viruses, the single-deletion mutants of KHV-T were significantly attenuated in vivo, and immersion of juvenile carp in water containing high doses of the double mutant caused almost no fatalities. Nevertheless, the deletion mutants induced similar levels of KHV-specific serum antibodies to the parental wild-type virus, and conferred solid protection against disease after challenge with wild-type KHV. For the convenient differentiation of DNA samples prepared from gill swabs of carp infected with wild-type and TK-deleted KHV we developed a triplex real-time PCR. Thus, KHV-TΔDUT/TK might be suitable as a genetic DIVA vaccine in the field.

Triplex Real-Time PCR without DNA Extraction for the Monitoring of Meningococcal Disease.

Detection of Neisseria meningitidis has become less time- and resource-intensive with a monoplex direct real-time PCR (drt-PCR) to amplify genes from clinical specimens without DNA extraction. To further improve efficiency, we evaluated two triplex drt-PCR assays for the detection of meningococcal serogroups AWX and BCY. The sensitivity and specificity of the triplex assays were assessed using 228 cerebrospinal fluid (CSF) specimens from meningitis patients and compared to the monoplex for six serogroups. The lower limit of detection range for six serogroup-specific drt-PCR assays was 178–5264 CFU/mL by monoplex and 68–2221 CFU/mL by triplex. The triplex and monoplex showed 100% agreement for six serogroups and the triplex assays achieved similar sensitivity and specificity estimates as the monoplex drt-PCR assays. Our triplex method reduces the time and cost of processing CSF specimens by characterizing six serogroups with only two assays, which is particularly important for testing large numbers of specimens for N. meningitidis surveillance.

Molecular detection of Toxoplasma gondii in feathered game intended for human consumption in the Czech Republic

Toxoplasma gondii is an important ubiquitous protozoan parasite, which can infect almost all warm-blooded vertebrates, including humans. The diagnosis of T. gondii infection is crucial for the prevention, surveillance, and control of its transmission. Here, a triplex real-time PCR assay targeting the B1 gene and 529rep element was used to determine the presence of T. gondii in feathered game (Anas platyrhynchos and Phasianus colchicus) hunted in the Czech Republic. The prevalence of T. gondii was 5.4% in wild ducks (n = 280) and 3.4% in common pheasants (n = 350). Additionally, genotyping of 28 T. gondii-positive samples revealed the presence of archetypal genotypes II and III as well as non-archetypal genotypes combining both type II and III alleles. Our results suggest that consumption of feathered game could pose a risk of T. gondii transmission to humans in the Czech Republic.

Simultaneous identification of bovine and equine DNA in milks and dairy products inferred from triplex TaqMan real-time PCR technique

Koumiss is a popular dairy product in many lands, traditionally prepared from mare milk with spontaneous fermentation. Mare milk and its fermented derivates are more expensive than cow milk and its fermented derivates, and the possibility exists for producers and dealers to adulterate equine products with bovine items. In this work, we described the development of a triplex real-time PCR based on species-specific TaqMan probes for identification of bovine and equine DNA in milks and dairy products. In addition, a novel designed endogenous control was simultaneously amplified to eliminate possible false negatives. With this methodology, bovine and equine DNA were specifically identified by employing developed primers and probes. The limits of detection of this method were 0.001 ng for cow milk, yogurt, and mare milk, and 0.005 ng for sour soup and koumiss, respectively. In addition, the triplex real-time PCR assay for authentication of animal-derived products was effectively validated using binary DNA and milk mixtures, exhibiting well in terms of specificity, sensitivity, and reproducibility. In short, the triplex PCR assay was verified to be a time-saving and money-saving technique for the identification of bovine and equine DNA in milks and dairy products.

Vérification en portée A d’une méthode de PCR triplexe pour la détection de Chlamydia trachomatis, Neisseria gonorrhoeae et Mycoplasma genitalium

Method verification, in range A, of a triplex real time PCR for the detection of Chlamydia trachomatis, Neisseria gonorrhoeae and Mycoplasma genitaliumIn 2017, at the Beauvais hospital laboratory, a real time PCR system has been acquired. This work describes the method verification of a real time PCR kit, Urethritis basic®, FTD, in range A, for the qualitative detection of Chlamydia trachomatis (CT), Neisseria gonorrhoeae (NG) and Mycoplasma genitalium (MG). According to the ISO 15189 standard, a risk analysis and a verification of some performance criteria are performed on site. Intermediate precision for NG is evaluated on two samples giving equivocal results. Following runs gives negative results. Comparison between the new and the previous end-point PCR method (GenoQuick®CT, Hain Lifescience) for the detection of CT is performed on 46 samples. Four samples show discordant results (all positive with the previous method and negative with the new one). Accuracy is assessed by two EQA (External Quality Assessment) for CT and NG and gave expected results. Our tests of carry-over contamination, by alternating positive and negative samples, did not identify any contamination. Finally, we implemented continuous verification by Levey-Jennings charts established using threshold cycles of controls. This work let to conclude on the ability of the method while confirming the interest of controlling equivocal NG results. In addition, it provides a tool to continuously monitor the performance.

Development of a triplex real-time PCR for simultaneous detection of allergenic ingredients in processed food

SYBR Green real-time or quantitative PCR (Q-PCR) is a suitable system in which to establish a multiplex method to detect allergenic ingredients in food. In this study, a triplex Q-PCR method was developed to detect trace amounts of peanut, soybean and sesame in processed food. Specific PCR primer sets were designed and the concentration of the primers used in the triplex PCR was optimised. The triplex method showed high specificity and sensitivity which were similar to those of the simplex method, and it was applied for the detection of allergenic ingredients in commercially available processed food. The results demonstrate that the developed triplex Q-PCR is a quick, reliable and efficient method for the detection of allergenic ingredients in processed food.

The blackfly vectors and transmission of Onchocerca volvulus in Mahenge, south eastern Tanzania

The Mahenge Mountains onchocerciasis focus in south eastern Tanzania was historically one of the most heavily infected areas in the country. The vectors of Onchocerca volvulus are mainly Simulium damnosum complex blackflies, but a species of the Simulium neavei group may also contribute to transmission in some areas. The only detailed studies of parasite transmission in Mahenge were conducted in the late 1960s. The taxonomy of the S. damnosum complex has since been revised and onchocerciasis control through annual community directed treatment with ivermectin (CDTI) commenced in 1997. This study aimed to provide a cytogenetic and molecular update of the S. damnosum complex cytoforms present in Mahenge, and to evaluate the current status of O. volvulus transmission by blackflies following 19 years of annual CDTI.Rivers were surveyed to identify sites of S. damnosum s.l. breeding among the eastern slopes of the mountains, and human landing collections of adult female blackflies were made close to breeding sites. Identification of S. damnosum complex cytoforms was by cytotaxonomy of late-instar larvae and ITS1 amplicon size polymorphisms of larvae and adults. Adult blackflies were pool screened for O. volvulus infection using a triplex real-time PCR. The cytoforms ‘Nkusi’, Simulium kilibanum and ‘Turiani’ were found breeding in perennial rivers. ‘Nkusi’ and S. kilibanum were collected on human bait at 7/7 catch sites and possessed ITS1 profiles most closely resembling the molecular forms ‘Nkusi J’ and S. kilibanum ‘T’. Whereas ‘Turiani’ was present in rivers, it was not collected on human bait and appears to be zoophilic. Simulium nyasalandicum was collected in low numbers on human bait at 3/7 catch sites. In total, 12,452 S. damnosum s.l. were pool screened and O. volvulus infection was detected in 97/104 pools of bodies and 51/104 pools of heads. The estimated percentage of S. damnosum s.l. carrying infective L3 stage parasites was 0.57% (95% CI 0.43%–0.74%).Onchocerca volvulus transmission by S. damnosum s.l. is continuing in the Mahenge Mountains after 19 years of annual CDTI. Infection rates appear similar to those reported in the 1960s, but a more detailed study is required to fully understand the epidemiological significance of the ongoing transmission. These results provide further evidence that annual CDTI may be insufficient to eliminate the parasite in formerly hyperendemic foci.

Triplex real-time PCR method for the qualitative detection of European and American foulbrood in honeybee

The bacteria Melissococcus plutonius and Paenibacillus larvae, causative agents of respectively European and American foulbrood, damage honeybee health worldwide. Here, we present a specific and sensitive qualitative triplex real-time PCR method to detect simultaneously those microbial agents and a honeybee gene, validated through a study involving 7 laboratories through Europe.

Triplex real-time PCR detection of three quarantine Phytophthora pathogens infecting Malus Miller

In order to develop a simultaneous and specific molecular detection of the three quarantine Phytophthora pathogens, Phytophthora hibernalis, Phytophthora cambivora and Phytophthora syringae that infect Malus Miller, three pairs of real-time PCR primers (PH-F/PH-R, PC-F/PC-R and PS-F/PS-R) and three probes (PH-Pr, PC-Pr and PS-Pr) labeled with HEX, FAM and ROX, respectively, were designed for P. hibernalis, P. cambivora and P. syringae by alignment analyses of enolase (Enol), ras-like protein Ypt1 and HSP90 gene sequences with other Phytophthora spp. Black Hole Quencher 1 (BHQ1) was used for P. hibernalis and P. cambivora and BHQ2 for P. syringae. Through the optimization of the reaction conditions, a triplex real-time PCR simultaneous detection for the three Phytophthora species infecting Malus Miller was developed. It could achieve simultaneous and specific detection with a sensitivity of 2 × 10−4, 2 × 10−4 and 2 × 10−2 ng/μL genomic DNA, respectively, for P. hibernalis, P. cambivora and P. syringae.

Cross-priming amplification-based lateral flow strip as a novel tool for rapid on-site detection of wild-type pseudorabies virus

Pseudorabies (PR), also called as Aujeszky’s disease, is an important infectious disease of pigs and other mammals caused by pseudorabies virus (PRV). This paper presents a novel assay based on cross-priming amplification in combination with gold nanoparticle lateral flow strip (CAP-strip) for rapid and on-site detection of wild-type PRV. In the assay, FITC and biotin were labeled at the 5′-ends of the two probes, respectively, resulting in amplified products labeled with either FITC or biotin at the 5′-end. Then the amplified products (biotin-dsDNA-FITC), as novel targets, were recognized by standardized strips. The assay had excellent visualization results from 2.0 × 102 to 2.0 × 108 copies of PRV and the detection limit was determined to be 200 copies. No cross-reactivity was observed with several common porcine viruses. When testing a total of 293 field swine samples, the agreement between the CPA-strip assay and a triplex real-time PCR or virus isolation were 100% (293/293) or 97.3% (285/293). Collectively, the assay is specific, sensitive and convenient that enables rapid, on-site diagnosis of PRV infections.

Novel motB as a potential predictive tool for identification of B. cereus, B. thuringiensis and differentiation from other Bacillus species by triplex real-time PCR

Quantitative triplex real-time PCR (qPCR) offers an alternative method for detection of bacterial contamination. It provides quantitation of the number of gene copies. In our study, we established a qPCR assay to detect and quantify the specificity towards Bacillus cereus and B. thuringiensis. The assay was designed to detect a 280 bp fragment of motB gene encoding the flagellar motor protein, specific for detection of B. cereus and B. thuringiensis, excluding other group species B. pseudomycoides, B. mycoides and B. weihenstephanensis. Specificity of the assay was confirmed with 111 strains belonging to Bacillus cereus group and performed against 58 B. cereus, 50 B. thuringiensis, 3 other Bacillus bacteria and 9 non-Bacillus bacteria. Detection limit was determined for each assay. Direct analysis of samples revealed the specificity towards identification and characterization of B. cereus group cultured in nutrient media. Based on results, it was observed that motB showed 97% specificity towards B. cereus strains, 98% for B. thuringiensis but other B. cereus group showed less sensitivity (0%), thus, provides an efficient tool to identify B. cereus and B. thuringiensis. Further, environmental and food samples do not require band isolation, re-amplification or sequence identification. Thus, reducing the time and cost of analysis.

One-step cross-genogroup multiplex RT-qPCR with an internal control system for the detection of infectious pancreatic necrosis virus (IPNV)

Infectious pancreatic necrosis virus (IPNV) causes great losses in fish hatcheries world-wide. The detection of IPNV can be challenging in certain circumstances, particularly due to low viral load and the genetic variability of this RNA virus. For the first time, this project created a quantitative triplex real-time reverse transcription PCR (RT-qPCR), including an endogenous control system, for specific, sensitive and rapid detection of IPNV in routine diagnostics. Multiple sequence alignment of 46 nucleotide sequences of the segment A genome obtained from the NCBI database allowed the design of two RT-qPCR systems covering the IPNV genogroup 1 and genogroups 2–5, respectively. The completed triplex RT-qPCR including a salmonid-specific endogenous control showed high specificity and an analytical sensitivity of 20–40 oligonucleotide copies. Testing of dilution series of virus-loaded cell culture suspensions proved equality of the triplex RT-qPCR with virus detection in cell culture and a higher sensitivity than conventional RT-PCR in field samples. In comparative studies of a total of 77 field samples tested, 51 showed identical positive and 19 identical negative results in cell culture and the triplex RT-qPCR. However, seven other samples yielded positive results in the triplex RT-qPCR, but negative results in cell culture.