Prediction of tensile modulus based on parameters of crystalline structure in polyethylene terephthalate with cold crystallization ability

This work aims to adopt a simple modulus prediction method for the crystalline poly(ethylene-terephthalate) (PET), which has strong cold-crystallization ability. Based on a single melting curve generated by calorimetry, crystallinity and average melting temperature can easily be evaluated and consequently, tensile modulus can be predicted. Nonetheless, in the case of polymers with cold crystallization behavior, such as PET, the melting process is affected by cold crystallization, impeding the simple calculation of the aforementioned important parameters. In this paper, the techniques to eradicate cold crystallization during calorimetry are presented. Accordingly, the results of a tensile modulus prediction model are presented and discussed. The crystallization and melting characteristics of PET were measured by differential scanning calorimetry (DSC). The mechanical properties of the specimens were estimated by standardized tensile tests. The specimens, which were used for mechanical tests were fabricated using conventional injection molding. The samples were annealed at different temperatures in order to obtain different crystalline structures. The results clearly indicate that the prediction technique is capable to describe the tensile modulus of PET accurately in the case of very diverse crystalline structures.

Highly Sensitive Detection of PIK3CA Mutations by Looping-Out Probes-Based Melting Curve Analysis

PIK3CA mutations have important therapeutic and prognostic implications in various cancer types. However, highly sensitive detection of PIK3CA hotspot mutations in heterogeneous tumor samples remains a challenge in clinical settings. To establish a rapid PCR assay for highly sensitive detection of multiple PIK3CA hotspot mutations. We described a novel melting curve analysis-based assay using looping-out probes that can enrich target mutations in the background of excess wild-type and concurrently reveal the presence of mutations. The analytical and clinical performance of the assay were evaluated. The developed assay could detect 10 PIK3CA hotspot mutations at a mutant allele fraction of 0.05-0.5% within 2 h in a single step. Analysis of 82 breast cancer tissue samples revealed 43 samples with PIK3CA mutations, 28 of which were confirmed by Sanger sequencing. Further testing of 175 colorectal cancer tissue samples showed that 24 samples contained PIK3CA mutations and 19 samples were confirmed by Sanger sequencing. Droplet digital PCR supported that all mutation-containing samples undetected by sequencing contained mutations with a low allele fraction. The rapidity, ease of use, high sensitivity and accuracy make the new assay a potential screening tool for PIK3CA mutations in clinical laboratories.

Multiplex polymerase spiral reaction for simultaneous detection of Salmonella typhimurium and Staphylococcus aureus

Salmonella typhimurium (S. typhimurium) and Staphylococcus aureus (S. aureus) are common food-borne pahogens that cause food poisoning in humans. In this study, we developed a method for the simultaneous determination of S. typhimurium and S. aureus based on multiplex polymerase spiral reaction (m-PSR) and melting curve analysis. Two pairs of primers were designed specifically to target the conserved invA gene of S. typhimurium and nuc gene of S. aureus, and the nucleic acid amplification reaction was achieved under isothermal conditions in the same reaction tube for 40 min at 61 °C, melting curve analysis of the amplification product was carried out. The distinct mean melting temperature allowed simultaneous differentiation of the two target bacteria in the m-PSR assay. The limit of detection of S. typhimurium and S. aureus that could be detected simultaneously was 4.1 × 10^-4 ng genomic DNA and 2 × 10¹ CFU/mL pure bacterial culture. Based on this method, analysis of artificially contaminated samples showed excellent sensitivity and specificity consistent with those of pure bacterial cultures. This method is rapid, simultaneous and promises to be a useful tool for the detection of food-borne pathogens in the food industry.

Diversity of Microbial Functional Genes Should Be Considered During the Interpretation of the qPCR Melting Curves

Soil microorganisms play an essential role in biogeochemical cycles. One approach to study these microbial communities is quantifying functional genes by quantitative PCR (qPCR), in which a melting curve analysis is usually assessed to confirm that a single PCR product is being quantified. However, the high diversity of functional genes in environmental samples could generate more than one peak in those curves, so the presence of two or multiple peaks does not always indicate nonspecific amplification. Here, we analyzed the taxonomic diversity of soil microorganisms harboring functional genes involved in nitrogen (N) and phosphorus (P) cycles, based on a database of genomes and metagenomes, and predicted the melting curve profiles of these genes. These functional genes were spread across many bacterial phyla, but mainly Proteobacteria and Actinobacteria. In general, the melting curves exhibited more than one peak or peaks with shoulders, mainly related to the variation of the nucleotide composition of the genes and the expected size of the amplicons. These results indicate that the melting curves of functional genes from environmental samples should be carefully evaluated, being in silico analyses a cost-effective way to identify inherent sequence diversity and avoid interpreting multiple peaks always as unspecific amplifications.

Multiplex detection of five common respiratory pathogens from bronchoalveolar lavages using high resolution melting curve analysis

Background

The study describes the application of the multiplex high-resolution melting curve (MHRM) assay for the simultaneous detection of five common bacterial pathogens (Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii and Escherichia coli) directly from bronchoalveolar lavage samples.

Results

Our MHRM assay successfully identified all five respiratory pathogens in less than 5 h, with five separate melting curves with specific melt peak temperatures (Tm). The different Tm were characterized by peaks of 78.1 ± 0.4 °C for S. aureus, 83.3 ± 0.1 °C for A. baumannii, 86.7 ± 0.2 °C for E. coli, 90.5 ± 0.1 °C for K. pneumoniae, 94.5 ± 0.2 °C for P. aeruginosa. The overall sensitivity and specificity of MHRM were 100% and 88.8–100%, respectively.

Conclusions

Our MHRM assay offers a simple and fast alternative to culture approach for simultaneous detection of five major bacterial lower respiratory tract infection pathogens. Utilization of this assay can help clinicians initiate prompt and appropriate antimicrobial treatment, towards reducing the morbidity and mortality of severe respiratory infections.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02558-2.

Single nucleotide polymorphism genotyping of ALDH2 gene based on asymmetric PCR and fluorescent probe-mediated melting curves

Detection of single nucleotide polymorphisms (SNPs) is of great value in precision medicine. The polymorphism of the aldehyde dehydrogenase 2 (ALDH2) gene is caused by a G1510A transition, resulting in the substitution of glutamic acid by lysine at position 487. People of different ALDH2 genotypes show different susceptibility to cancer, metabolic diseases, etc. SNP analysis based on fluorescent probe-mediated melting curves is a relatively efficient and cost-effective method. Genomic DNA extracted from 100 whole blood samples was subjected to polymorphisms mutational analysis using asymmetric PCR and probe-mediated melting curves. Then a certain number of samples from each genotype were randomly selected for direct sequencing verification. The new assay can be performed in 2 h without post-PCR processing such as gel electrophoresis and validated by direct sequencing in a blind study with 100% concordance. Moreover, comparing the detection of polymorphisms of ALDH2 with the clinics, and an overall agreement of 100% (100/100) was demonstrated. Our study has shown a high level of concordance between DNA sequencing, which is suitable for the detection of clinical specimens. Based on the concept of probe-mediated melting curves, we further developed this platform as a universal strategy for the detection of polymorphisms related to folate metabolism.

Web-based LinRegPCR: application for the visualization and analysis of (RT)-qPCR amplification and melting data

BACKGROUND

The analyses of amplification and melting curves have been shown to provide valuable information on the quality of the individual reactions in quantitative PCR (qPCR) experiments and to result in more reliable and reproducible quantitative results.

IMPLEMENTATION

The main steps in the amplification curve analysis are (1) a unique baseline subtraction, not using the ground phase cycles, (2) PCR efficiency determination from the exponential phase of the individual reactions, (3) setting a common quantification threshold and (4) calculation of the efficiency-corrected target quantity with the common threshold, efficiency per assay and C_q per reaction. The melting curve analysis encompasses smoothing of the observed fluorescence data, normalization to remove product-independent fluorescence loss, peak calling and assessment of the correct peak by comparing its melting temperature with the known melting temperature of the intended amplification product.

RESULTS

The LinRegPCR web application provides visualization and analysis of a single qPCR run. The user interface displays the analysis results on the amplification curve analysis and melting curve analysis in tables and graphs in which deviant reactions are highlighted. The annotated results in the tables can be exported for calculation of gene-expression ratios, fold-change between experimental conditions and further statistical analysis. Web-based LinRegPCR addresses two types of users, wet-lab scientists analyzing the amplification and melting curves of their own qPCR experiments and bioinformaticians creating pipelines for analysis of series of qPCR experiments by splitting its functionality into a stand-alone back-end RDML (Real-time PCR Data Markup Language) Python library and several companion applications for data visualization, analysis and interactive access. The use of the RDML data standard enables machine independent storage and exchange of qPCR data and the RDML-Tools assist with the import of qPCR data from the files exported by the qPCR instrument.

CONCLUSIONS

The combined implementation of these analyses in the newly developed web-based LinRegPCR ( https://www.gear-genomics.com/rdml-tools/ ) is platform independent and much faster than the original Windows-based versions of the LinRegPCR program. Moreover, web-based LinRegPCR includes a novel statistical outlier detection and the combination of amplification and melting curve analyses allows direct validation of the amplification product and reporting of reactions that amplify artefacts.

Rapid screening method for the detection of SARS-CoV-2 variants of concern

Background

Comprehensive and up-to-date monitoring of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOC) is crucial as these are characterized by their increased transmissibility, immune evasion and virulence.

Objectives

To describe the wide-scale implementation of a reverse transcriptase polymerase chain reaction (RT-PCR) multiple variants assay with melting curve analysis as a routine procedure.

Study design

We prospectively performed multiple variants RT-PCR on consecutive SARS-CoV-2 RT-PCR positive samples from patients, healthcare workers and nursing home residents from our hospital catchment area. This technique was implemented in our automated Roche FLOW system with a turn-around time of 6 h.

Results

Between February 1 and May 2, 2021, 989 samples were tested by the variant RT-PCR. Our method was validated by comparison of variant RT-PCR to whole genome sequencing testing. We observed an increase over time in the proportion of UK variant that became the dominant variant, and the concurrent emergence of the South-African and Brazilian variants. Prompt public health responses for infection control were possible because of this rapid screening method, resulting in early detection and reduction of unnoticed spread of VOC as early as possible.

Conclusion

A variant RT-PCR with additional melting curve analyses is a feasible, rapid and efficient screening strategy that can be implemented in routine microbiological laboratories.

A Novel 2-dimensional Multiplex qPCR Assay for Single-Tube Detection of Nine Human Herpesviruses

Human herpesviruses are double-stranded DNA viruses that are classified into nine species. More than 90% of adults are ever infected with one or more herpesviruses. The symptoms of infection with different herpesviruses are diverse ranging from mild or asymptomatic infections to deadly diseases such as aggressive lymphomas and sarcomas. Timely and accurate detection of herpesvirus infection is critical for clinical management and treatment. In this study, we established a single-tube nonuple qPCR assay for detection of all nine herpesviruses using a 2-D multiplex qPCR method with a house-keeping gene as the internal control. The novel assay can detect and distinguish different herpesviruses with 30 to 300 copies per 25 µL single-tube reaction, and does not cross-react with 20 other human viruses, including DNA and RNA viruses. The robustness of the novel assay was evaluated using 170 clinical samples. The novel assay showed a high consistency (100%) with the single qPCR assay for HHVs detection. The features of simple, rapid, high sensitivity, specificity, and low cost make this assay a high potential to be widely used in clinical diagnosis and patient treatment.

Single probe PCR melting curve analysis MTHFR C677T SNP sites

BACKGROUND

The detection and analysis of methylene tetrahydrofolate reductase (MTHFR) C677T single nucleotide polymorphism (SNP) from blood samples is time-consuming and costly. We aimed to establish a method to detect these SNPs by direct whole blood PCR and without DNA extraction.

METHODS

Probes modified by different fluorescent groups on the same sequence were designed. Various MTHFR genotypes from direct blood PCR experiments were used to verify the similarity of the obtained and sequencing results. The SNP sites adjacent to the MTHFR C677T SNP were used to verify whether the method can accurately distinguish these sites.

RESULTS

The ROX probe was found to be the most suitable for this study. We tested 291 samples with 1 μL whole blood as a template, and obtained 126, 43, and 122 cases of C677C, C677T, and C677 C/T genotypes, respectively. The melting curve was consistent with the sequencing results. The detection limit was approximately 1000 white blood cells/μL. Through PCR and the melting curve method, the adjacent sites were accurately distinguished.

CONCLUSION

We established a reliable, simple, rapid, and low-cost direct blood PCR method for the detection of MTHFR C677T SNPs. This could also be used as a potential diagnostic tool for a variety of diseases.

Quantification of Ammonia Oxidizing Bacterial Abundances in Environmental Samples by Quantitative-PCR

Quantitative-PCR (qPCR) enables the quantification of specific DNA targets, such as functional or phylogenetic marker genes associated with environmental samples. During each qPCR cycle, the number of copies of a gene (or region) of interest in DNA samples is determined in real time using a fluorescence-based label and compared to a standard serial dilution. Here, we describe a qPCR method to quantify the ammonia oxidizing bacteria involved in the first step of nitrification, using the amoA gene as a proxy of their abundance. The preparation of the standards from environmental samples and qPCR is presented in detail for specifically quantifying microbial abundance in environmental samples such as soil.

Single-tube detection of nine bacterial antibiotic-resistance genes by a 2-dimensional multiplex qPCR assay based on fluorescence and melting temperature

Simple, multiplex qPCR methods are advantages for rapid molecular diagnosis of multiple antibiotics-resistant genes simultaneously. However, the number of genes can be detected in a single reaction tube is often limited by the fluorescence channels of a real-time PCR instrument. In this study, we developed a simple 2-D multiplex qPCR method by combining the probe colors and amplicon Tm values to overcome the mechanical limit of the machine. The principle of the novel assay was validated by detection of nine bacterial antibiotic-resistance genes (KPC, NDM, VIM, OXA-48, GES, CIT, EBC, ACC and DHA) in a single reaction tube. This assay is highly sensitive within a range of 30-3000 copies per reaction. The simplicity, rapidity, high sensitivity and specificity, and low cost of the novel method make it a promising tool for developing clinical diagnostic kits for monitoring resistance and other genetic determinants of infectious diseases.

Genotyping on blood and buccal cells using loop-mediated isothermal amplification in healthy humans

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Genetic variations contribute to phenotypic individual vulnerabilities to sleep debt.

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LAMP-MC is a recently developed method to characterize Single Nucleotide Polymorphism.

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Detection is performed directly from whole blood or buccal cells.

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LAMP-MC method produced specific melting curves for 5 sleep debt-related SNPs.

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High concordance of results was observed between LAMP-MC and Taqman referent method.

Genetic variations contribute to phenotypic individual vulnerabilities to sleep debt, particularly for five single nucleotide polymorphisms (SNPs). Loop-mediated isothermal amplification and melting curve analysis (LAMP-MC) is a recently developed method to characterize SNPs. The aim of present study was to evaluate the LAMP-MC method on blood and buccal cells for detection of five SNPs of interest in healthy humans.

We first analyzed signals obtained from LAMP-MC method on 42 samples. Then we compared the results with those of referent TaqMan method.

The LAMP-MC method produced specific melting curves for the five SNPs. A high concordance of genotyping results was observed between the two methods for rs5751876_ADORA2A, rs1800629_TNF-α, rs73598374_ADA and rs228697_PER3 in blood and saliva (Cohen’s kappa coefficient >0.80). A good agreement ( = 0.61) was observed for rs4680_COMT in blood only.

LAMP-MC is a simple and reliable method to study genetic influences on health, sleep debt-related performance impairments and countermeasures.

Infectious bronchitis virus Mass-type (GI-1) and QX-like (GI-19) genotyping and vaccine differentiation using SYBR green RT-qPCR paired with melting curve analysis

Infectious Bronchitis Virus (IBV) is a highly contagious virus of chicken, causing huge economic losses in the poultry industry. Many genotypes circulate in a given area, and optimal protection relies on vaccination with live attenuated vaccines of the same genotype. As these live vaccines are derived from field viruses and circulate, understanding the prevalence of different IBV genotypes in any area is complex. In a recent study, the genome comparison of an IBV QX vaccine and its progenitor field strain led to the identification of vaccine markers. Here we developed a simplex SYBRgreen RT-qPCR assay for differentiation between QX-like field and vaccine strains and a multiplex SYBRgreen RT-qPCR assay for IBV genotyping with melting curve analysis, as each virus produced distinct and reliable melting peaks. Both the simplex and the multiplex assays showed excellent efficiency, sensitivity and specificity representing a low cost diagnostic tool for IBV genotyping and vaccine differentiation.

A novel multiplex PCR for virus detection by melting curve analysis

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Taqman probe based melting curve analysis can detect and distinguish six respiratory viruses simultaneously.

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The multiplex PCR established here has a good analytical sensitivity and specificity.

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The accordance rate between the multiplex PCR and direct fluorescent antibody testing was high.

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Taqman probe based melting curve analysis is well suited to multiple virus detection.

Background

Rapid and accurate laboratory diagnoses of viral infections are crucial for the management and treatment of patients with viral infections. Conventional methods for virus detection are labourious, time consuming, and only a single virus can be analysed in one assay.

Objectives

The objective of this study was to develop a novel real-time PCR method for multiple virus detection by melting curve analysis using Taqman probes in a single reaction.

Study design

As a model, six respiratory viruses were detected in one tube using three fluorophores. The specificity was assessed by cross-reaction tests with other common respiratory pathogens. The analytical sensitivity was assessed by testing the limit of detection of the assay using artificial plasmids as the positive template. The clinical evaluation of the established assay was evaluated for the detection of respiratory viruses in clinical samples, and the results were compared with direct fluorescent antibody testing (DFA).

Results

The six respiratory viruses were clearly distinguished by their respective melting temperature values in the corresponding fluorescence detection channels. No cross reactions were observed by cross reaction tests. The detection limits of this assay were 2 to 2 × 10³ copies per reaction for each virus. The clinical evaluation of this assay was demonstrated by analysing 352 clinical samples, and 67(19.0%) samples were positive for at least one virus. The accordance rate between the established PCR and DFA testing was high, and ranged from 94.57% to 100%.

Conclusions

Taqman probe-based melting curve analysis is well suited for detection of multiple viruses in clinical and research laboratories because of its high throughput, reliability, and cost savings.

Development of a melting-curve based multiplex real-time PCR assay for simultaneous detection of Streptococcus agalactiae and genes encoding resistance to macrolides and lincosamides

Background

Streptococcus agalactiae or Group B Streptococcus (GBS) remains the leading cause of infections in newborns worldwilde. Prenatal GBS screening of pregnant women for vaginal-rectal colonization is recommended in many countries to manage appropriate intrapartum antimicrobial prophylaxis for those identified as carriers. In this study, a novel melting-curve based multiplex real-time PCR assay for the simultaneous detection of GBS and macrolide and lincosamide resistance markers was developed. The usefulness of the assay was evaluated for rapid and accurate prenatal GBS screening.

Methods

One hundred two pregnant women who were at 35–37 weeks of gestation were enrolled in this study. The analytical performance of the multiplex real-time PCR was first tested using a panel of reference and clinical bacterial and fungal strains. To test the clinical performance, vaginal-rectal swabs were obtained from pregnant women who were seen at the teaching hospital for regular prenatal care. The results of real-time were compared with those obtained from microbiological analyses.

Results

The real-time PCR assay showed 100% specificity and a limit of detection of 10⁴ colony forming units equivalent per reaction. The prevalence of GBS colonization among the population studied was 15.7% (16/102) based on a positive culture and the real-time PCR results. Agreement between the two assays was found for 11 (68.75%) GBS colonized women. Using the culture-based results as a reference, the multiplex real-time PCR had a sensitivity of 91.7% (11/12, CI 59.7–99.6%), a specificity of 95.5% (86/90, CI 89.8–98.7%), a positive predictive value of 73.3% (11/15, CI 44.8–91.1%) and a negative predictive value of 98.9% (86/87, CI 92.9–99.9%).

Conclusion

The multiplex real-time PCR is a rapid, affordable and sensitive assay for direct detection of GBS in vaginal-rectal swabs.

Electronic supplementary material

The online version of this article (10.1186/s12884-018-1774-5) contains supplementary material, which is available to authorized users.

High-resolution melting PCR assay, applicable for diagnostics and screening studies, allowing detection and differentiation of several Babesia spp. infecting humans and animals

The goal of the study was to design a single tube PCR test for detection and differentiation of Babesia species in DNA samples obtained from diverse biological materials. A multiplex, single tube PCR test was designed for amplification of approximately 400 bp region of the Babesia 18S rRNA gene. Universal primers were designed to match DNA of multiple Babesia spp. and to have low levels of similarity to DNA sequences of other intracellular protozoa and Babesia hosts. The PCR products amplified from Babesia DNA isolated from human, dog, rodent, deer, and tick samples were subjected to high-resolution melting analysis for Babesia species identification. The designed test allowed detection and differentiation of four Babesia species, three zoonotic (B. microti, B. divergens, B. venatorum) and one that is generally not considered zoonotic—Babesia canis. Both detection and identification of all four species were possible based on the HRM curves of the PCR products in samples obtained from the following: humans, dogs, rodents, and ticks. No cross-reactivity with DNA of Babesia hosts or Plasmodium falciparum and Toxoplasma gondii was observed. The lack of cross-reactivity with P. falciparum DNA might allow using the assay in endemic malaria areas. The designed assay is the first PCR-based test for detection and differentiation of several Babesia spp. of medical and veterinary importance, in a single tube reaction. The results of the study show that the designed assay for Babesia detection and identification could be a practical and inexpensive tool for diagnostics and screening studies of diverse biological materials.

Development of a multiplex real-time PCR assay for phylogenetic analysis of Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is among major pathogens causing 80-90% of all episodes of urinary tract infections (UTIs). Recently, E. coli strains are divided into eight main phylogenetic groups including A, B1, B2, C, D, E, F, and clade I. This study was aimed to develop a rapid, sensitive, and specific multiplex real time PCR method capable of detecting phylogenetic groups of E. coli strains. This study was carried out on E. coli strains (isolated from the patient with UTI) in which the presence of all seven target genes had been confirmed in our previous phylogenetic study. An EvaGreen-based singleplex and multiplex real-time PCR with melting curve analysis was designed for simultaneous detection and differentiation of these genes. The primers were selected mainly based on the production of amplicons with melting temperatures (T_m) ranging from 82°C to 93°C and temperature difference of more than 1.5°C between each peak.The multiplex real-time PCR assays that have been developed in the present study were successful in detecting the eight main phylogenetic groups. Seven distinct melting peaks were discriminated, with Tm value of 93±0.8 for arpA, 89.2±0.1for chuA, 86.5±0.1 for yjaA, 82.3±0.2 for TspE4C2, 87.8±0.1for trpAgpC, 85.4±0.6 for arpAgpE genes, and 91±0.5 for the internal control. To our knowledge, this study is the first melting curve-based real-time PCR assay developed for simultaneous and discrete detection of these seven target genes. Our findings showed that this assay has the potential to be a rapid, reliable and cost-effective alternative for routine phylotyping of E. coli strains.

Silver ion-mediated killing of a food pathogen: Melting curve analysis data of silver resistance genes and growth curve data

Limited antibacterial activity of silver ions leached from silver-impregnated food contact materials could be due to: 1) the presence of silver resistance genes in tested bacteria; or 2) lack of susceptibility to silver ion-mediated killing in the bacterial strain (K. Williams, L. Valencia, K. Gokulan, R. Trbojevich, S. Khare, 2016 [1]). This study contains data to address the specificity of silver resistance genes in Salmonella Typhimurium during the real time PCR using melting curve analysis and an assessment of the minimum inhibitory concentration of silver ions for Salmonella.

Molecular detection of Mycoplasma haemomuris subspecies using dnaK-targeted real-time PCR with SYBR Green I and melting curve analysis

Hemoplasmas cause severe infections in mammals, but these pathogens are difficult to detect and identify at the species and subspecies level because of the need for time-consuming sequence based methods. Here, we used real-time PCR with SYBR Green I targeting of the dnaK gene followed by standard melting curve analysis to achieve rapid detection and differentiation of the Mycoplasma haemomuris subspecies 'Candidatus Mycoplasma haemomuris subsp. musculi' and 'Candidatus M. haemomuris subsp. ratti'. The melting temperatures of the PCR products, 84.63 ± 0.14 °C for 'Candidatus M. haemomuris subsp. musculi', and 80.72 ± 0.16 °C for 'Candidatus M. haemomuris subsp. ratti', provided clear differentiation between them. Murine hemoplasma DNA samples, which were used as references, were confirmed for species by an analysis of 16S rRNA sequences. The protocol described herein provides a new rapid detection and identification method suitable for use with two recognized subspecies of M. haemomuris.

Rapid detection and grouping of porcine bocaviruses by an EvaGreen(®) based multiplex real-time PCR assay using melting curve analysis

Several novel porcine bocaviruses (PBoVs) have been identified in pigs in recent years and association of these viruses with respiratory signs or diarrhea has been suggested. In this study, an EvaGreen(®)-based multiplex real-time PCR (EG-mPCR) with melting curve analysis was developed for simultaneous detection and grouping of novel PBoVs into the same genogroups G1, G2 and G3. Each target produced a specific amplicon with a melting peak of 81.3 ± 0.34 °C for PBoV G1, 78.2 ± 0.37 °C for PBoV G2, and 85.0 ± 0.29 °C for PBoV G3. Non-specific reactions were not observed when other pig viruses were used to assess the EG-mPCR assay. The sensitivity of the EG-mPCR assay using purified plasmid constructs containing the specific viral target fragments was 100 copies for PBoV G1, 50 for PBoV G2 and 100 for PBoV G3. The assay is able to detect and distinguish three PBoV groups with intra-assay and inter-assay variations ranging from 0.13 to 1.59%. The newly established EG-mPCR assay was validated with 227 field samples from pigs. PBoV G1, G2 and G3 was detected in 15.0%, 25.1% and 41.9% of the investigated samples and coinfections of two or three PBoV groups were also detected in 25.1% of the cases, indicating that all PBoV groups are prevalent in Chinese pigs. The agreement of the EG-mPCR assay with an EvaGreen-based singleplex real-time PCR (EG-sPCR) assay was 99.1%. This EG-mPCR will serve as a rapid, sensitive, reliable and cost effective alternative for routine surveillance testing of multiple PBoVs in pigs and will enhance our understanding of the epidemiological features and possible also pathogenetic changes associated with these viruses in pigs.

Real-time PCR using FRET technology for Old World cutaneous leishmaniasis species differentiation

Background

Recently, there has been a re-emergence of cutaneous leishmaniasis in endemic countries and an increase in imported cases in non-endemic countries by travelers, workers, expatriates, immigrants, and military force personnel. Old World cutaneous leishmaniasis is caused primarily by Leishmania major, L. tropica and L. aethiopica. Despite their low sensitivity, diagnosis traditionally includes microscopic and histopathological examinations, and in vitro cultivation. Several conventional PCR techniques have been developed for species identification, which are time-consuming and labour-intensive. Real-time PCR using SYBR green dye, although provides rapid detection, may generate false positive signals. Therefore, a rapid and easy method such as a FRET-based real-time PCR would improve not only the turn-around time of diagnosing Old World cutaneous Leishmania species but will also increase its specificity and sensitivity.

Methods

A FRET-based real-time PCR assay which amplifies the cathepsin L-like cysteine protease B gene encoding a major Leishmania antigen was developed to differentiate L. major, L. tropica, and L. aethiopica in one single step using one set of primers and probes. Assay performance was tested on cutaneous and visceral strains of Leishmania parasite cultures and isolates of other protozoan parasites as well as human biopsy specimen.

Results

The assay readily differentiates between the three Old World cutaneous leishmaniasis species based on their melting curve characteristics. A single Tm at 55.2 ± 0.5 °C for L. aethiopica strains was distinguished from a single Tm at 57.4 ± 0.2 °C for L. major strains. A double curve with melting peaks at 66.6 ± 0.1 °C and 48.1 ± 0.5 °C or 55.8 ± 0.6 °C was observed for all L. tropica strains. The assay was further tested on biopsy specimens, which showed 100 % agreement with results obtained from isoenzyme electrophoresis and Sanger sequencing.

Conclusion

Currently, there are no published data on real-time PCR using FRET technology to differentiate between Old World cutaneous Leishmania species. In summary, our assay based on specific hybridization addresses the limitations of previous PCR technology and provides a single step, reliable method of species identification and rapid diagnostic applications.

A probe-free four-tube real-time PCR assay for simultaneous detection of twelve enteric viruses and bacteria

OBJECTIVES

We aim to develop a multiplex real-time PCR assay to detect the most common pathogens causing community outbreaks of diarrhea.

METHODS

Four reaction systems of fluorescence dye-based real-time PCR assay were performed to amplify genes of norovirus, sapovirus, rotavirus, astrovirus, adenovirus, Campylobacter jejuni, Yersinia enterocolitica, Vibrio parahaemolyticus, Salmonella spp., Escherichia coli, and Shigella spp. PCR products of each pathogen were identified by characteristic peaks in melting curves.

RESULTS

The assay was able to achieve detection limit of 50 copies/reaction for each individual virus target, and 140-500CFU/mL for each individual bacterium target. A total of 122 clinical specimens from hospitalized children with acute diarrhea were used to evaluate the assay. The clinical sensitivity was very similar to that of reference methods. Norovirus genogroup II revealed the highest detectable rate (45/122, 36.9%). Coinfection was found in 28 out of 122 (23%) clinical specimens.

CONCLUSION

This assay proved to be a cost-effective, sensitive and reliable method for simultaneous detection of enteric viruses and bacteria.

Rapid detection of α-thalassaemia alleles of --(SEA)/, -α(3.7)/ and -α(4.2)/ using a dual labelling, self-quenching hybridization probe/melting curve analysis

OBJECTIVES

The aim of the study was to set up an alternative automatic molecular diagnostic method for deletional α-thalassaemia mutations without gel electrophoresis.

METHODS

Based on the sequence variation within the two Z boxes and melting curve analysis of dually labelled probes, a real-time PCR assay was developed and validated for the rapid detection of major α-genotypes (--(SEA)/αα, --(SEA)/-α(3.7), --(SEA)/-α(4.2), --(SEA)/--(SEA), -α(3.7)/-α(3.7) and -α(4.2)/-α(4.2)).

RESULTS

Samples with the -α(3.7)/-α(3.7), -α(4.2)/-α(4.2), --(SEA)/αα, --(SEA)/-α(3.7), --(SEA)/-α(4.2), and --(SEA)/--(SEA) genotypes could be clearly distinguished. The accuracy of this technique for these samples was 100% sensitivity and specificity.

CONCLUSION

This technique is rapid and reliable, demonstrating feasibility for use in large-scale population screening and prenatal diagnosis of deletional Hb H disease and Hb Bart's hydrops fetalis.

Picosecond acoustics method for measuring the thermodynamical properties of solids and liquids at high pressure and high temperature

Based on the original combination of picosecond acoustics and diamond anvils cell, recent improvements to accurately measure hypersonic sound velocities of liquids and solids under extreme conditions are described. To illustrate the capability of this technique, results are given on the pressure and temperature dependence of acoustic properties for three prototypical cases: polycrystal (iron), single-crystal (silicon) and liquid (mercury) samples. It is shown that such technique also enables the determination of the density as a function of pressure for liquids, of the complete set of elastic constants for single crystals, and of the melting curve for any kind of material. High pressure ultrafast acoustic spectroscopy technique clearly opens opportunities to measure thermodynamical properties under previously unattainable extreme conditions. Beyond physics, this state-of-the-art experiment would thus be useful in many other fields such as nonlinear acoustics, oceanography, petrology, in of view. A brief description of new developments and future directions of works conclude the article.

Detection and Identification of Six Foodborne Bacteria by Two-tube Multiplex Real Time PCR and Melting Curve Analysis

OBJECTIVE

This study is aimed to develop a two-tube melting curve-based multiplex real time PCR assay (MCMRT-PCR) for the simultaneous detection of six common foodborne pathogenic bacteria (diarrhoeagenic Escherichia coli, Salmonella, and Shigella in tube 1, Staphylococcus aureus, Vibrio parahaemolyticus, and Listeria monocytogenes in tube 2).

METHODS

A two-tube MCMRT-PCR assay was performed on 7900HT Fast Real-Time PCR System (Applied Biosystems, USA). Amplification by PCR was optimized to obtain high efficiency. The sensitivity and specificity of assays were investigated.

RESULTS

The detection limit of optimized MCMRT-PCR assay was 3.9×102 CFU/mL for S. aureus, 4.4×102 CFU/mL for L. monocytogenes, 3.0×102 CFU/mL for Salmonella, 2.5×102 CFU/mL for Shigella, 2.1×102 CFU/mL for V. parahaemolyticus, and 1.2×102 CFU/mL for E. coli. The feasibility of MCMRT-PCR was further evaluated using artificially contaminated milk, the sensitivity was at the level of 105 CFU/mL.

CONCLUSION

A two-tube MCMRT-PCR assay using six primer sets was developed for detection of multiple pathogens. Our findings demonstrates that the proposed two-tube assay is reliable, useful and rapid for simultaneous detection of six foodborne pathogenic bacteria with an intended application in provincial Centers for Diseases Control and Prevention (CDC).