Duplex Real-time PCR Research Articles

A Novel Method for Rapid Screening of Salmonidae Ingredients and Accurate Detection of Atlantic Salmon (Salmo salar) Simultaneously Using Duplex Real-Time PCR Coupled with Melting Curve Analysis

The substitution of ingredients with Salmonidae, particularly Salmo salar, has led to widespread reports of financial losses and health risks globally, emphasizing the urgent need for the development of a rapid and precise method for species identification. The aim of the present study was to develop a novel method for the rapid screening of Salmonidae ingredients and the accurate detection of S. salar simultaneously using multiplex real-time PCR coupled with melting curve analysis. Specifically, primer sets specific for S. salar and Salmonidae were cross-confirmed. Moreover, the reaction system and conditions of a real-time duplex PCR were optimized, and the proposed methodology was verified, proving that the assay has good specificity and sensitivity. Clear and distinguishable melting peaks, with expected Tm values of around 80 °C (S. salar) and 84 °C (Salmonidae), were observed for twelve products, proving the presence of S. salar. However, four products were not derived from S. salar, but they could have belonged to another species within the Salmonidae family due to the presence of only one specific melting peak at a Tm value of about 84 °C. Therefore, the novel assay in the present study allows for the fast and accurate screening of Salmonidae ingredients and the detection of S. salar simultaneously.

Development and evaluation of a duplex real-time multienzyme isothermal rapid amplification assay for the detection of hypervirulent Klebsiella pneumoniae in clinical spiked blood specimens

ObjectivesOur objective was to establish a rapid and precise method for detecting hypervirulent Klebsiella pneumoniae (hvKP) by utilizing a duplex real-time multienzyme isothermal rapid amplification (real-time MIRA) and to evaluate its performance in clinical spiked blood specimens. MethodsThe research comprised two phases: an initial pilot study to establish the methodology and a clinical validation study to assess its effectiveness. In the pilot phase, we designed specific primers and probes targeting the hvKP pg344 and incA genes and subsequently developed a duplex real-time MIRA assay to evaluate its detection limits, specificity, and efficiency. In the clinical validation phase, we analyzed thirty-three spiked blood specimens using the duplex real-time MIRA assay. ResultsThe duplex real-time MIRA assay demonstrated no cross-reactivity with other strains. Sensitivity experiments confirmed that the assay had a detection limit as low as 8 × 102 CFU per reaction for hvKP. The analysis of clinical spiked blood specimens indicated that the sensitivity and specificity of the duplex real-time MIRA assay were on par with those of duplex real-time PCR. ConclusionsThese findings confirm that the duplex real-time MIRA assay is a fast, straightforward, and dependable method for detecting hvKP.

Duplex Real-Time Fluorescent Quantitative PCR Assays for the Detection of Toxigenic Microcystis Genotypes Based on SNP/InDel Variation in mcy Gene Cluster.

In this study, the toxigenic characteristics of 14 strains of Microcystis were analyzed, and single nucleotide polymorphism (SNP) and insertion/deletion (InDel) loci in microcystinsynthetase (mcy)geneclusters were screened. Based on SNP and InDel loci associated with the toxigenic characteristics, primers andTaqMan or Cycling fluorescent probes were designed to develop duplex real-time fluorescent quantitative PCR (FQ-PCR) assays. After evaluating specificity and sensitivity, these assays were applied to detect the toxigenic Microcystis genotypes in a shrimp pond where Microcystis blooms occurred. The results showed a total of 2155 SNP loci and 66 InDel loci were obtained, of which 12 SNP loci and 5 InDel loci were associated with the toxigenic characteristics. Three duplex real-time FQ-PCR assays were developed, each of which could quantify two genotypes of toxigenic Microcystis. These FQ-PCR assays were highly specific, and two Cycling assays were more sensitive than TaqMan assay. In the shrimp pond, six genotypes of toxigenic Microcystis were detected using the developed FQ-PCR assays, indicating that above genotyping assays have the potential for quantitative analysis of the toxigenic Microcystis genotypes in natural water.

Identifying a novel Listeria innocua subgroup and enhancing Listeria detection in grain: A duplex real-time PCR approach informed by comparative genomic analysis

This study focuses on enhancing the detection accuracy of Listeria species in the food industry, particularly addressing the challenges posed by closely related strains that complicate pathogen identification. Detecting Listeria monocytogenes, a key psychrotolerant foodborne pathogen, is crucial in the food industry. Although real-time PCR-based methods targeting the iap gene are commonly employed for identification, our investigation of L. innocua strains isolated from wheat in South Korea revealed false positives, indicating an imperative for more accurate detection approaches. We used comparative genomic analysis to identify a novel subgroup of L. innocua with closer genomic affiliations to L. monocytogenes. Consequently, we developed new primer and probe sets for more accurate detection of both L. monocytogenes and L. innocua, demonstrating high specificity and selectivity. Additionally, we revealed the importance of food matrix effects, particularly color pigments, in the design of diagnostic assays. These advances provide insight into genomic differences between L. monocytogenes and L. innocua, and pioneer new detection techniques for Listeria species.

Prevalence and quantitative assessment of foodborne viruses on the imported mussels in Polish market

The aim of this study was an assessment of the prevalence of human enteric viruses such as norovirus (NoV) and hepatitis A and E virus (HAV, HEV) in mussels sold on the Polish market. In addition, the presence of human (hAdV) and swine (pAdV) adenoviruses as indicators of faecal contamination of shellfish was also studied. In total, 246 shellfish samples representing 41 batches of blue and Mediterranean mussels were purchased from Polish seafood wholesalers. Shellfish were processed according to the method in ISO 15216-2:2019 followed by isolation of viral nucleic acids using NucliSens®Magnetic Extraction Reagents (bioMérieux). For virus detection several duplex real-time PCR protocols with incorporated internal amplification controls (IAC) were used. The presence of human enteric viruses was shown in 42 shellfish samples (17.1%). The most frequently detected were NoV (41 samples; 16.7%) followed by HEV (1 sample; 0.4%). None of the samples was positive for HAV, hAdV or pAdV. 15 shellfish batches (36.6%) were virus positive. By the use of Bayesian inference, a true seasonal and country related virus prevalence in shellfish was estimated. NoV GI was more frequently detected in Dutch mussels (18.9%; 95% CI: 6.7%–34.0%), while NoV GII was more frequent in Danish mussels (17.1%; 95% CI: 5.8%–32.5%). However significant differences in virus prevalence in individual and shellfish batches between producing countries were not shown. A seasonal virus distribution pattern in shellfish samples was observed. Lower level of NoV contamination was found in mussels harvested during spring-summer (0.0%–1.3%, 95% CI: 0.1%–4.8%) compared to the fall-winter season (13.0%–20.7%, 95% CI: 6.1%–31.2%). For shellfish batches, a similar seasonal correlation was only observed for NoV GII. The monitoring of marketed shellfish would be an essential tool allowing a reduction of the number of viral food-borne outbreaks.

Quantification of Pork, Chicken, Beef, and Sheep Contents in Meat Products Using Duplex Real-Time PCR.

Accurate methods for meat speciation and quantification are essential for ensuring the supply of safe and wholesome meat and composite products with animal origins to negate the potential associated hazards, aid classification of consignments at the import control system, and thwart food fraud committed for financial gain. To better enhance meat safety control and combat food fraud, this study developed two duplex real-time polymerase chain reaction (real-time PCR) systems specifically designed for chicken, pork, sheep, and beef, using single-copy, chromosomally encoded, species-specific gene sequences to accurately measure the content of each meat type in meat products. DNA extracted from the raw and boiled reference materials prepared in varying proportions (ranging from 1% to 75%) were used in the development of the duplex assay to derive calibration factors to determine the meat content in different meat products. The method was further validated using proficiency test samples and market monitoring samples. Our findings showed that this method exhibits high specificity and sensitivity, with a significant accuracy range of 0.14% to 24.07% in quantifying the four meat types in both raw and processed meat products. Validation results further confirmed the effectiveness of our method in accurately quantifying meat content. Thus, we have demonstrated the duplex qPCR assays as promising approaches for implementation in routine analysis to strengthen meat safety control systems and combat meat fraud, thereby safeguarding consumer health and trust in the meat industry.

Development of a real-time duplex PCR assay for simultaneously diagnosis of KHV and CEV in common carp and koi

Koi herpesvirus (KHV) and carp edema virus (CEV) are potential risks for the koi trade and for global common carp aquaculture. Due to the severe impact of both viruses, a robust diagnostic tool was required, capable of detecting and distinguishing both infections with high accuracy and precision. The aim of this study was to describe a real-time duplex TaqMan PCR assay for simultaneous detection of KHV and CEV in common carp and koi. Two pairs of primers with two TaqMan probes were used to amplify specific and conserved regions of KHV and CEV DNA. This assay was confirmed to be sensitive and specific. Limit of detections of the assay were 15 DNA copies/µL for KHV and 150 DNA copies/µL for CEV, respectively. This assay was able to identify and distinguish CEV and KHV, but was unable to identify other pathogens and sample matrices. For clinical validation, 18 KHV and CEV positive samples each, as well as 12 negative samples were tested with three different test methods, i.e., real-time duplex PCR, real-time simplex PCR, and conventional PCR. All three tests provide optimal conformity of results. The results showed that real-time duplex PCR was able to detect the presence and distinguish each pathogen in infected fish. This real-time duplex PCR assay is a rapid, sensitive, and specific test for detecting KHV and CEV in carp fish, thus it can be considered a valid alternative assay in aquaculture clinical laboratories.
 
 Keywords: Cyprinus carpio, CEV, diagnostic, KHV, real-time duplex PCR
 
 ABSTRAK
 
 Koi herpesvirus (KHV) dan carp edema virus (CEV) merupakan risiko potensial untuk perdagangan koi dan budidaya ikan mas global. Karena dampak dari keduanya yang parah, maka diperlukan perangkat diagnostik yang tangguh, yang mampu mendeteksi dan membedakan keduanya dengan akurasi dan presisi yang tinggi. Tujuan dari penelitian ini adalah menjabarkan pengujian real time TaqMan PCR dupleks untuk mendeteksi KHV dan CEV pada ikan mas dan koi secara simultan dalam satu reaksi. Dua pasang primer dengan dua TaqMan probe digunakan untuk mengamplifikasi wilayah spesifik dan lestari dari DNA KHV dan CEV. Pengujian ini terbukti sensitif dan spesifik. Sensitivitas dari pengujian ini adalah 15 kopi DNA/µL untuk KHV dan 150 kopi DNA/µL untuk CEV. Pengujian ini mampu mengidentifikasi dan membedakan CEV dan KHV, tetapi tidak dapat mengidentifikasi patogen lain dan matriks sampel. Untuk validasi klinis, masing-masing 18 sampel positif KHV dan CEV, serta 12 sampel negatif diuji dengan tiga metode pengujian yang berbeda, yaitu real-time PCR dupleks, real-time PCR tunggal dan PCR konvensional. Ketiga pengujian tersebut memberikan kesesuaian hasil yang optimal. Hasil penelitian menunjukkan bahwa real-time PCR dupleks mampu mendeteksi keberadaan dan membedakan setiap patogen pada ikan yang terinfeksi. Uji real-time PCR dupleks ini merupakan pengujian yang cepat, sensitif, dan spesifik untuk mendeteksi KHV dan CEV pada ikan koi dan mas, sehingga dapat dipertimbangkan sebagai pengujian alternatif yang valid di laboratorium klinis akuakultur.
 
 Kata kunci: Cyprinus carpio, CEV, diagnostik, KHV, real-time PCR dupleks

Morphological, Molecular and Genomic Identification and Characterisation of Monilinia fructicola in Prunus persica from Portugal

In Portugal, the Cova da Beira region is well-known for the production of Prunus spp. and is considered the main peach production area in the country. In the spring of 2021 and 2022, field surveys in peach and nectarine orchards showed symptoms of decline such as cankers, gummosis, dry branches, abortion of flowers, mummified fruits and the partial or total death of some plants. Brown rot is caused by three species of the genus Monilinia, M. fructigena, M. laxa and M. fructicola, the last is an OEPP/EPPO A2 quarantine organism on peach trees. Brown rot disease had previously been described in the Cova da Beira region, however, the recent high mortality and severity of symptoms raised doubts as to the species involved. Symptomatic plant material was collected from thirteen orchards and used for fungal isolation and molecular detection according to the OEPP/EPPO standard. M. fructicola was confirmed morphologically and molecularly in two orchards, and molecularly (duplex real-time PCR) detected in two others. Whole genome sequencing using Oxford Nanopore MinION was also carried out to confirm the identification. Pathogenicity tests were performed on peach, nectarine and sweet cherry fruit according to Koch’s postulates. Based on all the results obtained, we report the first detection of M. fructicola in P. persica in Portugal.

Duplex real-time PCR assay for the simultaneous detection of Ophiostoma novo-ulmi and Geosmithia spp. in elm wood and insect vectors

Dutch elm disease (DED) is a destructive tracheomycosis caused by Ophiostoma novo-ulmi, an ascomycete probably originating in East-Asia that is devastating natural elm populations throughout Europe, North America and Asia. The fungus is mainly spread by elm bark beetles that complete their life cycle between healthy and diseased elms. Recently, it has been highlighted that some fungi of the genus Geosmithia, which are similarly well associated with bark beetles, seem to also play a role in the DED pathosystem acting as mycoparasites of O. novo-ulmi. Although some relationship between the fungi is clear, the biological cycle of Geosmithia spp. within the DED cycle is still partly unclear, as is the role of Geosmithia spp. in association with the bark beetles. In this work, we tried to clarify these aspects by developing a qPCR duplex TaqMan assay to detect and quantify DNA of both fungi. The assay is extremely sensitive showing a limit of detection as low as 2 fg μl–1 for both fungi. We collected woody samples from healthy and infected elm trees throughout the beetle life cycle. All healthy elm samples were negative for both Geosmithia spp. and O. novo-ulmi DNA. Geosmithia spp. are never present in infected, but living trees, while they are present in frass of elm bark beetles (EBB – Scolytus spp.) and at each stage of the EBB life cycle in much higher quantities than O. novo-ulmi. This work provides a better understanding of the role and interactions occurring amongst the main players of the DED pathosystem.

Duplex real-time PCR assays for the simultaneous detection and quantification of Botryosphaeriaceae species causing canker diseases in woody crops

Duplex real-time PCR assays for the simultaneous detection and quantification of Botryosphaeriaceae species causing canker diseases in woody crops

Differential detection of sheep and goat meat using duplex real-time PCR and high-resolution melt analysis

Authenticity in meat and meat products is of paramount importance in preventing adulteration and ensuring food safety. Since morphologically indistinct samples like sheep and goat meat requires accurate and sensitive differentiation, we developed and validated a duplex real-time polymerase chain reaction (qPCR) assay with high-resolution melt analysis (HRMA) for simultaneous identification of sheep and goat meat. Species-specific amplicons with melting temperature of 78 °C for goat and 80 °C for sheep (with associated standard errors) was identified. The assay was optimized for basic PCR parameters and the HRMA detection was standardized based on melt curve shape, color and inflexion points. The absolute limit of detection (LODabs) and limit of quantification (LOQ) of the assay were found to be 0.39 ng and 0.78 ng of target DNA respectively. A sensitivity of 0.1% was obtained for both sheep and goat meat. The relative limit of detection (LODrel) was also found to be 5%. The linearity and efficiency were evaluated in both simplex and duplex assays. The assay applicability was evaluated using proficiency test samples and commercially available raw and processed meat samples. The obtained results showed that this closed-tube qPCR-HRMA method can be a rapid and sensitive detection technique for meat speciation.

Intracellular persistence of Leishmania tarentolae in primary canine macrophage cells

Leishmania tarentolae is a non-pathogenic species first isolated from geckoes in the Mediterranean basin. The finding that dogs test positive against both Leishmania infantum and L. tarentolae raises questions regarding the ability of the latter species to persist and adapt to new hosts. This study aimed to evaluate in vitro the capability of L. tarentolae to colonize, survive and persist in canine primary monocyte-derived mononuclear cells. Monocytes were isolated from dog whole blood samples and placed in 24-well plates for differentiation into macrophages and for incubation with L. tarentolae field-isolated strains (RI-325 and SF-178) and laboratory (LEM-124) strain; the parasite burden was assessed at different time points post-infection. The L. infantum laboratory strain (MON-1) was used as control. Infection parameters were evaluated by microscopy, counting the number of amastigotes/200 infected cells, and by duplex real-time PCR from supernatants and detached cells. Similar to L. infantum, L. tarentolae strains developed into round-shaped amastigote-like forms, with higher infection rates detected at 4 h followed by an overall decrease until 48 h. RI-325 presented also a higher infection rate at 72 h. Data showed that L. tarentolae strains infect and persist inside in vitro primary canine mononuclear cells, opening new perspectives for further laboratory studies.

Duplex real-time PCR assays for the simultaneous detection and quantification of Botryosphaeriaceae species causing canker diseases in woody crops

Duplex real-time PCR assays for the simultaneous detection and quantification of Botryosphaeriaceae species causing canker diseases in woody crops

Rapid diagnosis of different goose astrovirus genotypes with Taqman-based duplex real-time quantitative PCR

Rapid diagnosis of different goose astrovirus genotypes with Taqman-based duplex real-time quantitative PCR

Molecular Diagnosis of Leishmaniasis in Spain: Development and Validation of Ready-To-Use Gel-Form Nested and Real-Time PCRs To Detect Leishmania spp.

Leishmaniasis is an endemic parasitic disease in at least 98 countries. In Spain, it is considered a zoonosis caused by Leishmania infantum, with an annual incidence of 0.62 cases/100,000 inhabitants. The predominant clinical manifestations are the cutaneous (CL) and visceral forms (VL), and the diagnosis is performed by parasitological, serological, and molecular tests. At the WHO Collaborating Center for Leishmaniasis (WHOCCLeish), routine diagnostic tests are based on a nested PCR (Ln-PCR), culture, and serological tests. To simplify our PCR protocol, we aimed to develop and validate a ready-to-use nested gel-form PCR (LeishGelPCR) and a duplex real-time PCR (qPCR) that allowed simultaneous detection of Leishmania and mammalian DNA as an internal control (Leish-qPCR). Clinical validation was performed in 200 samples from the WHOCCLeish collection; 92 and 85 out of 94 and 87 samples were positive by LeishGelPCR and Leish-qPCR, respectively, showing a sensitivity of 98% in both approaches. The specificity was 100% for LeishGelPCR and 98% for Leish-qPCR. The limits of detection of both protocols were similar (0.5 and 0.2 parasites/reaction). Parasite loads in VL and CL forms were similar, although high loads were observed when invasive samples were tested. In conclusion, LeishGelPCR and Leish-qPCR showed excellent performance in the diagnosis of leishmaniasis. These new forms of 18S rRNA gene PCR are equivalent to Ln-PCR and can be introduced in the algorithm for CL and VL diagnosis. IMPORTANCE Although the gold standard for diagnosis of leishmaniasis is the microscopic observation of amastigotes, molecular techniques are becoming a cost-efficient alternative. Currently, PCR is a routine resource that is used in many reference microbiology laboratories. In this article, we have described two ways to improve the reproducibility and usability of the molecular detection of Leishmania spp. These new approaches could be introduced even in middle- and low-resource laboratories; one is a ready-to-use gel-form system of a nested PCR and the other is a real-time PCR. We show why molecular diagnosis is the best methodology to confirm a clinical suspicion of leishmaniasis with higher sensitivity than traditional methods, thus facilitating early diagnosis and timely treatment of human leishmaniasis.

Rapid diagnosis of duck Tembusu virus and goose astrovirus with TaqMan-based duplex real-time PCR.

The mixed infection of duck Tembusu virus (DTMUV) and goose astrovirus (GoAstV) is an important problem that endangers the goose industry. Although quantitative PCR has been widely used in monitoring these two viruses, there is no reliable method to detect them at the same time. In this study, by analyzing the published genomes of DTMUV and goose astrovirus genotype 2 (GoAstV-2) isolated in China, we found that both viruses have high conservation, showing 96.5 to 99.5% identities within different strains of DTMUV and GoAstV, respectively. Subsequently, PCR primers and TaqMan probes were designed to identify DTMUV and GoAstV-2, and different fluorescent reporters were given to two probes for differential diagnosis. Through the optimization and verification, this study finally developed a duplex TaqMan qPCR method that can simultaneously detect the above two viruses. The lower limits of detection were 100 copies/μL and 10 copies/μL for DTMUV and GoAstV-2 under optimal condition. The assay was also highly specific in detecting one or two viruses in various combinations in specimens, and provide tool for clinical diagnosis of mixed infections of viruses in goose.

Development and Validation of a New DIVA Real-Time PCR Allowing to Differentiate Wild-Type Lumpy Skin Disease Virus Strains, Including the Asian Recombinant Strains, from Neethling-Based Vaccine Strains.

The current epidemic in Asia, driven by LSDV recombinants, poses difficulties to existing DIVA PCR tests, as these do not differentiate between homologous vaccine strains and the recombinant strains. We, therefore, developed and validated a new duplex real-time PCR capable of differentiating Neethling-based vaccine strains from classical and recombinant wild-type strains that are currently circulating in Asia. The DIVA potential of this new assay, seen in the in silico evaluation, was confirmed on samples from LSDV infected and vaccinated animals and on isolates of LSDV recombinants (n = 12), vaccine (n = 5), and classic wild-type strains (n = 6). No cross-reactivity or a-specificity with other capripox viruses was observed under field conditions in non-capripox viral stocks and negative animals. The high analytical sensitivity is translated into a high diagnostic specificity as more than 70 samples were all correctly detected with Ct values very similar to those of a published first-line pan capripox real-time PCR. Finally, the low inter- and intra-run variability observed shows that the new DIVA PCR is very robust which facilitates its implementation in the lab. All validation parameters that are mentioned above indicate the potential of the newly developed test as a promising diagnostic tool which could help to control the current LSDV epidemic in Asia.

Duplex real-time PCR assay with high-resolution melt analysis for the detection and quantification of Listeria species and Listeria monocytogenes in meat products.

The online version contains supplementary material available at 10.1007/s13197-023-05695-2.

Simultaneous Detection of Salmonella spp. and Quantification of Campylobacter spp. in a Real-Time Duplex PCR: Myth or Reality?

In Europe, there is a process hygiene criterion for Salmonella and Campylobacter on broiler carcasses after chilling. The criterion gives indicative contamination values above which corrective actions are required by food business operators. The reference methods for verifying compliance with the criterion for Salmonella and Campylobacter are international standards EN ISO 6579-1 (2017) and EN ISO 10272-2 (2017), respectively. These methods are time-consuming and expensive for food business operators. Therefore, it would be advantageous to simultaneously detect Salmonella spp. and quantify Campylobacter in the same analysis, using the same sample after the pre-enrichment step for Salmonella recovery. A duplex PCR for Salmonella detection and Campylobacter spp. enumeration was developed. Considering the method as a whole, the LOD and LOQ for Campylobacter enumeration were slightly over the limit of 3 log CFU/g set by the process hygiene criterion. A comparison of the duplex PCR method developed with the ISO method on artificially contaminated bacterial suspensions and on naturally contaminated samples demonstrated a good correlation of the results for Campylobacter enumeration when the duplex PCR was performed on samples taken before or after the pre-enrichment step, but revealed a slight bias with a large standard deviation resulting in widely spaced limits of agreement.

Development of a direct duplex real-time PCR assay for rapid detection of domestic cat hepadnavirus.

Domestic cat hepadnavirus (DCH) is a novel hepadnavirus, first identified in 2018. DCH is generally detected using conventional PCR assays, which include time-consuming agarose gel electrophoresis. We developed a rapid, sensitive, and specific real-time PCR (rtPCR) assay for the detection of the DCH genome. To streamline the procedure, our rtPCR assay was carried out using blood samples, without DNA extraction. A consensus primers/probe set was designed based on the nucleotide sequences of the surface/polymerase gene of all DCH strains available in GenBank. To exclude the possibility that the PCR reaction was blocked by anticoagulants, we also used a primers/probe set for amplifying the cat beta-actin gene as a reference gene. Our direct duplex rtPCR assay had high sensitivity, with a limit of detection of 10 copies/μL of blood for DCH. Our direct duplex rtPCR assay should be a useful tool for DCH detection and surveillance.