Differential susceptibility of PCR reactions to inhibitors: an important and unrecognised phenomenon

Specifications of qPCR based epigenetic immune cell quantification

OBJECTIVES

Immune monitoring is an important aspect in diagnostics and clinical trials for patients with compromised immune systems. Flow cytometry is the standard method for immune cell counting but faces limitations. Best practice guidelines are available, but lack of standardization complicates compliance with e.g., in vitro diagnostic regulations. Limited sample availability forces immune monitoring to predominantly use population-based reference intervals. Epigenetic qPCR has evolved as alternative with broad applicability and low logistical demands. Analytical performance specifications (APS) have been defined for qPCR in several regulated fields including testing of genetically modified organisms or vector-shedding.

METHODS

APS were characterized using five epigenetic qPCR-based assays quantifying CD3+, CD4+, CD8+ T, B and NK cells in light of regulatory requirements.

RESULTS

Epigenetic qPCR meets all specifications including bias, variability, linearity, ruggedness and sample stability as suggested by pertinent guidelines and regulations. The assays were subsequently applied to capillary blood from 25 normal donors over a 28-day period. Index of individuality (IoI) and reference change values were determined to evaluate potential diagnostic gains of individual reference intervals. Analysis of the IoI suggests benefits for individual over population-based references. Reference change values (RCVs) show that changes of approx. Fifty percent from prior measurement are suggestive for clinically relevant changes in any of the 5 cell types.

CONCLUSIONS

The demonstrated precision, long-term stability and obtained RCVs render epigenetic cell counting a promising tool for immune monitoring in clinical trials and diagnosis.

Comparison of quantitative PCR and digital PCR assays for quantitative detection of infectious bronchitis virus (IBV) genome

The quantitative polymerase chain reaction (qPCR) technique is an extensively used molecular tool for the detection and quantification of viral genome load. However, since the qPCR assay is a relative quantification method that relies on an external calibration curve it has a lower assay precision and sensitivity. The digital PCR (dPCR) technique is a good alternative to the qPCR assay as it offers highly precise and direct quantification of viral genome load in samples. In this study, performance characteristics such as the quantification range, sensitivity, precision, and specificity of the dPCR technique was compared to qPCR technique for the detection and quantification of IBV genome loads in serial dilutions of IBV positive plasmid DNA, and IBV infected chicken tissue and swab samples. The quantification range of the qPCR assay was wider than that of the dPCR assay, however dPCR had a higher sensitivity compared to qPCR. The precision of quantification of DNA in plasmid samples in terms of repeatability and reproducibility of results was higher when using the dPCR assay compared to qPCR assay. The quantification results of IBV genome load in infected samples by the qPCR and dPCR assays displayed a high correlation. Hence, our findings suggest that dPCR could be used in avian virology research for improved precision and sensitivity in detection and quantification of viral genome loads.

First field study using Strong-LAMP for diagnosis of strongyloidiasis in Cubal, Angola

BACKGROUND

Strongyloides stercoralis infection is a common neglected tropical disease distributed worldwide, mainly in tropical and subtropical climates. The impact of S. stercoralis infections on human health ranges from mild asymptomatic infections to chronic strongyloidiasis unnoticeable until the host is immunosuppressed. In severe strongyloidiasis, a syndrome of hyperinfection and larval dissemination to various organs can occur with high mortality rates. The diagnosis of strongyloidiasis is challenging because of the absence of a single standard reference test with high sensitivity and specificity, which also makes it difficult to estimate the accuracy of other diagnostic tests. This study aimed to evaluate, for the first time, the use of an easy-to-perform loop-mediated isothermal amplification (LAMP) colorimetric assay (named Strong-LAMP) for the molecular screening of strongyloidiasis in stool samples from patients in a low-resource endemic area in Cubal, Angola. To compare different LAMP application scenarios, the performance of the Strong-LAMP under field conditions in Angola was reassessed in a well-equipped reference laboratory in Spain and compared with a quantitative polymerase chain reaction (qPCR) method.

METHODS

A total of 192 stool samples were collected from adult population in Cubal, Angola, and examined by parasitological methods (direct saline microscopy and Baermann's technique). DNA was extracted from each stool sample using a commercial kit and tested by the colorimetric Strong-LAMP assay for the detection of Strongyloides spp. under field conditions. Furthermore, all samples were shipped to a well-equipped laboratory in Spain, reanalysed by the same procedure and compared with a qPCR method. The overall results after testing were compared.

RESULTS

Strongyloides stercoralis larvae were identified by direct saline microscopy and Baermann in a total of 10/192 (5.2%) and 18/192 (9.4%) stool samples, respectively. Other helminth and protozoan species were also identified. The Strong-LAMP-positive results were visually detected in 69/192 (35.9%) stool samples. The comparison of Strong-LAMP results in field conditions and at a reference laboratory matched in a total of 146/192 (76.0%) samples. A total of 24/192 (12.5%) stool samples tested positive by qPCR.

CONCLUSIONS

This is the first study in which colorimetric Strong-LAMP has been clinically evaluated in a resource-poor strongyloidiasis endemic area. Strong-LAMP has been shown to be more effective in screening for strongyloidiasis than parasitological methods under field conditions and qPCR in the laboratory. Our Strong-LAMP has proven to be a field-friendly and highly accurate molecular test for the diagnosis of strongyloidiasis.

A qPCR Method to Assay Endonuclease Activity of Cas9-sgRNA Ribonucleoprotein Complexes

The CRISPR-Cas system has emerged as the most efficient genome editing technique for a wide range of cells. Delivery of the Cas9-sgRNA ribonucleoprotein complex (Cas9 RNP) has gained popularity. The objective of this study was to develop a quantitative polymerase chain reaction (qPCR)-based assay to quantify the double-strand break reaction mediated by Cas9 RNP. To accomplish this, the dextransucrase gene (dsr) from Leuconostoc citreum was selected as the target DNA. The Cas9 protein was produced using recombinant Escherichia coli BL21, and two sgRNAs were synthesized through in vitro transcription to facilitate binding with the dsr gene. Under optimized in vitro conditions, the 2.6 kb dsr DNA was specifically cleaved into 1.1 and 1.5 kb fragments by both Cas9-sgRNA365 and Cas9-sgRNA433. By monitoring changes in dsr concentration using qPCR, the endonuclease activities of the two Cas9 RNPs were measured, and their efficiencies were compared. Specifically, the specific activities of dsr365RNP and dsr433RNP were 28.74 and 34.48 (unit/μg RNP), respectively. The versatility of this method was also verified using different target genes, uracil phosphoribosyl transferase (upp) gene, of Bifidobacterium bifidum and specific sgRNAs. The assay method was also utilized to determine the impact of high electrical field on Cas9 RNP activity during an efficient electroporation process. Overall, the results demonstrated that the qPCR-based method is an effective tool for measuring the endonuclease activity of Cas9 RNP.

Detecting human cytomegalovirus in urine, vagina and saliva: Impact of biological fluids and storage durations and temperatures on CMV DNA recovery

Sample collection, transport and storage conditions vary in the human cytomegalovirus (CMV) shedding literature. Currently, limited data exist on the impact of biological fluids and pre-analytical sample handling on the detection of CMV DNA. To evaluate CMV DNA recovery from urine, vaginal fluid and saliva stored in different conditions, adult urine, vaginal and saliva fluids and swabs, stored with or without selected nucleic acid preservation media at various durations and temperatures, was compared by polymerase chain reaction (PCR) quantitation of spiked samples and self-collected urine (n = 45) and vaginal swabs (n = 58) from CMV seropositive pregnant women. There was a time-dependent reduction in CMV DNA recovery from urine, urine diluted in phosphate-buffered saline, and saliva stored at 2-8°C, but not from urine preserved in cobas® PCR transport media (CPM) (urine/CPM). For vaginal fluid, a reduction in recovery was evident after 7 days storage at 2-8°C. CMV DNA recovery over 91 days was similar between -80°C and -20°C storage for urine and vaginal swabs preserved in CPM, and saliva swabs preserved in eNAT® PCR transport media. A statistically significant change in CMV DNA recovery after 25 months storage (median) at -80°C was not observed for self-collected urine/CPM and vaginal swab/CPM from pregnant women. Taken together, recovery of CMV DNA is dependent on fluid type and storage conditions. To improve the validity and reliability of detection at different storage durations and temperatures, the use of nucleic acid preserving transport media at the point of collection for urine, vaginal fluid and saliva may be essential.

Effects of solvent-based adhesive removal on the subsequent dual analysis of fingerprint and DNA

The combined approach of classical fingerprinting and DNA profiling is a powerful tool in forensic investigations of latent "touch" traces. However, little attention has been paid to the organic solvents frequently used in dactyloscopic laboratories to facilitate the separation of adhesive evidence prior to fingerprint development and downstream effects on subsequent DNA profiling. In the present study, we tested a selection of adhesive removers (n = 9) and assessed their potential impact on DNA recovery and amplification by PCR. Thereby, we identified and characterized novel PCR inhibitors. All investigated chemicals contain volatile organic compounds that evaporate under normal indoor atmospheric conditions. Exposure to certain solvents resulted in increased DNA degradation, but only if evaporation was prevented. A series of adhesive-removal experiments were conducted with prepared mock evidence (self-adhesive postage stamps affixed to paper envelope) to investigate the impact of treatment time and the location of applied traces on DNA recovery and dactyloscopy, respectively. Due to the early onset of print decomposition, we found that only a short treatment time was compatible with the development of fingerprints on the adhesive side of a stamp. Solvents also removed DNA from the adhesive surface, thus resulting in a marked shift in the substrate distribution of recovered DNA from the stamp to the envelope, but not in the reverse direction. Furthermore, we observed that treatment with conventional fingerprint reagents lead to a significant reduction in the amounts of DNA recovered from stamps, while the additional use of adhesive removers did not significantly enhance this effect.

Extracellular circulating miRNAs as potential non-invasive biomarkers in non-small cell lung cancer patients

Non-small cell lung cancer (NSCLC) comprises 85% of all lung cancers and is a malignant condition resistant to advanced-stage treatment. Despite the advancement in detection and treatment techniques, the disease is taking a deadly toll worldwide, being the leading cause of cancer death every year. Current diagnostic methods do not ensure the detection of the disease at an early stage, nor can they predict the risk of its development. There is an urgent need to identify biomarkers that can help predict an individual's risk of developing NSCLC, distinguish NSCLC subtype, allow monitor disease and treatment progression which can improve patient survival. Micro RNAs (miRNAs) represent the class of small and non-coding RNAs involved in gene expression regulation, influencing many biological processes such as proliferation, differentiation, and carcinogenesis. Research reports significant differences in miRNA profiles between healthy and neoplastic tissues in NSCLC. Its abundant presence in biofluids, such as serum, blood, urine, and saliva, makes them easily detectable and does not require invasive collection techniques. Many studies support miRNAs' importance in detecting, predicting, and prognosis of NSCLC, indicating their utility as a promising biomarker. In this work, we reviewed up-to-date research focusing on biofluid miRNAs' role as a diagnostic tool in NSCLC cases. We also discussed the limitations of applying miRNAs as biomarkers and highlighted future areas of interest.

Drug Regulatory-Compliant Validation of a qPCR Assay for Bioanalysis Studies of a Cell Therapy Product with a Special Focus on Matrix Interferences in a Wide Range of Organ Tissues

Quantitative polymerase chain reaction (qPCR) has emerged as an important bioanalytical method for assessing the pharmacokinetics of human-cell-based medicinal products after xenotransplantation into immunodeficient mice. A particular challenge in bioanalytical qPCR studies is that the different tissues of the host organism can affect amplification efficiency and amplicon detection to varying degrees, and ignoring these matrix effects can easily cause a significant underestimation of the true number of target cells in a sample. Here, we describe the development and drug regulatory-compliant validation of a TaqMan® qPCR assay for the quantification of mesenchymal stromal cells in the range of 125 to 20,000 cells/200 µL lysate via the amplification of a human-specific, highly repetitive α-satellite DNA sequence of the chromosome 17 centromere region HSSATA17. An assessment of matrix effects in 14 different mouse tissues and blood revealed a wide range of spike recovery rates across the different tissue types, from 11 to 174%. Based on these observations, we propose performing systematic spike-and-recovery experiments during assay validation and correcting for the effects of the different tissue matrices on cell quantification in subsequent bioanalytical studies by multiplying the back-calculated cell number by tissue-specific factors derived from the inverse of the validated percent recovery rate.

COVID-19 PCR: frequency of internal control inhibition in clinical practice

Introduction

Diagnosis of COVID-19 (coronavirus disease 2019) is best performed with real-time (quantitative) PCR (qPCR), the most sensitive method for detection and quantification of viral RNA. Using the Centers for Disease Control and Prevention (CDC) protocol, for each sample tested for the virus, three qPCR tests are performed, targeting the viral genes N1 and N2, in addition to the internal control gene RNase P. Samples in which internal control fails to amplify should be labelled 'invalid'.

Methods

This study aims to determine the frequency of inhibition of the RNase P gene used as an internal control in qPCR tests for SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) in a reference hospital in Southern Brazil during the COVID-19 pandemic (1 February 2021 to 31 March 2021).

Results

A total 10, 311 samples were available for analysis. The mean cycle threshold (Ct) value for the RNAse P gene was 26.65 and the standard deviation was 3.18. A total of 252 samples were inhibited (2.4%) during the study period: amongst these, 77 (30.5%) showed late amplifications (beyond 2 standard deviations from the mean Ct value), and 175 (69.4%) revealed no fluorescence at all for the RNase P gene.

Conclusions

This study showed a low percentage of inhibition using RNase P as an internal control in COVID-19 PCRs using the CDC protocol, thus proving the effectiveness of this protocol for identification of SARS-CoV-2 in clinical samples. Re-extraction was efficacious for samples that showed little or no fluorescence for the RNase P gene.

A standardized method for plasma extracellular vesicle isolation and size distribution analysis

The following protocol describes our workflow for isolation and quantification of plasma extracellular vesicles (EVs). It requires limited sample volume so that the scientific value of specimens is maximized. These steps include isolation of vesicles by automated size exclusion chromatography and quantification by tunable resistive pulse sensing. This workflow optimizes reproducibility by minimizing variations in processing, handling, and storage of EVs. EVs have significant diagnostic and therapeutic potential, but clinical application is limited by disparate methods of data collection. This standardized protocol is scalable and ensures efficient recovery of physiologically intact EVs that may be used in a variety of downstream biochemical and functional analyses. Simultaneous measurement quantifies EV concentration and size distribution absolutely. Absolute quantification corrects for variations in EV number and size, offering a novel method of standardization in downstream applications.

The Inhibition and Variability of Two Different RT-qPCR Assays Used for Quantifying SARS-CoV-2 RNA in Wastewater

Faecal shedding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its subsequent detection in wastewater turned the spotlight onto wastewater-based epidemiology (WBE) for monitoring the coronavirus-disease 2019 (COVID-19) pandemic. WBE for SARS-CoV-2 has been deployed in 70 countries, providing insights into disease prevalence, forecasting and the spatiotemporal tracking and emergence of SARS-CoV-2 variants. Wastewater, however, is a complex sample matrix containing numerous reverse transcription quantitative PCR (RT-qPCR) inhibitors whose concentration and diversity are influenced by factors including population size, surrounding industry and agriculture and climate. Such differences in the RT-qPCR inhibitor profile are likely to impact the quality of data produced by WBE and potentially produce erroneous results.To help determine the possible impact of RT-qPCR assay on data quality, two assays employed by different laboratories within the UK's SARS-CoV-2 wastewater monitoring programme were assessed in the Cefas laboratory in Weymouth, UK. The assays were based on Fast Virus (FV) and qScript (qS) chemistries using the same primers and probes, but at different concentrations and under different cycling conditions. Bovine serum albumin and MgSO4 were also added to the FV assay reaction mixture. Two-hundred and eighty-six samples were analysed, and an external control RNA (EC RNA)-based method was used to measure RT-qPCR inhibition. Compared with qS, FV showed a 40.5% reduction in mean inhibition and a 57.0% reduction in inter-sample inhibition variability. A 4.1-fold increase in SARS-CoV-2 quantification was seen for FV relative to qS; partially due (1.5-fold) to differences in reverse transcription efficiency and the use of a dsDNA standard. Analytical variability was reduced by 51.2% using FV while qS increased the number of SARS-CoV-2 negative samples by 2.6-fold. This study indicates the importance of thorough method optimisation for RT-qPCR-based WBE which should be performed using a selection of samples which are representative of the physiochemical properties of wastewater. Furthermore, RT-qPCR inhibition, analytical variability and reverse transcription efficiency should be key considerations during assay optimisation. A standardised framework for the optimisation and validation of WBE procedures should be formed including concessions for emergency response situations that would allow flexibility in the process to address the difficult balance between the urgency of providing data and the availability of resources.

Direct, precise, enzyme-free detection of miR-103–3p in real samples by microgels with highly specific molecular beacons

Low abundance, small size, and sequence similarities render microRNA (miRNAs) detection challenging, particularly in real samples, where quantifying weakly expressed miRNAs can be arduous due to interference of more abundant molecules. The standard quantitative reverse transcription polymerase chain reaction (qRT-PCR) requires multiple steps, thermal cycles, and costly enzymatic reactions that can negatively affect results. Here we present a direct, precise, enzyme-free assay based on microgels particles conjugating molecular beacons (MB) capable of optically detecting low abundant miRNAs in real samples. We validate the applicability of microgels assay using qRT-PCR as a reference technology. As a relevant case, we chose miR-103-3p, a valuable diagnostic biomarker for breast cancer, both in serum samples and MCF7 cells. As a result, microgels assay quantifies miRNA molecules at room temperature in a single step, 1 h (vs. 4 hrs for qRT-PCR) without complementary DNA synthesis, amplification, or expensive reagents. Microgels assay exhibits femtomolar sensitivity, single nucleotide specificity, and a wide linear range (10²-10⁷ fM) (wider than qRT-PCR), with low sample consumption (2 μL) and excellent linearity (R²= 0.98). To test the selectivity of the microgel assay in real samples, MCF7 cells were considered where the pool of 8 other miRNAs were further upregulated with respect to miRNA 103-3p. In such complex environments, microgels assay selectively detects the miRNA target, mainly due to MB advanced stability and specificity as well as high microgel antifouling properties. These results show the reliability of microgels assay to detect miRNAs in real samples.

Gene Expression Quantification from Pathogenic Bacterial Biofilms by Quantitative PCR

Quantitative PCR (qPCR) is one of the most used techniques to quantify gene expression in bacterial biofilms due to its easiness, sensitivity, and robustness. However, several practical aspects need to be considered to obtain accurate and reliable results. Here, we describe a detailed and optimized protocol to quantify mRNA transcripts from bacterial biofilms using qPCR, including pieces of advice to improve RNA quality, which ultimately increases the accuracy, consistency, and relevance of gene expression data.

Optimized Method for Bacterial Nucleic Acid Extraction from Positive Blood Culture Broth for Whole-Genome Sequencing, Resistance Phenotype Prediction, and Downstream Molecular Applications

The application of direct metagenomic sequencing from positive blood culture broth may solve the challenges of sequencing from low-bacterial-load blood samples in patients with sepsis. Forty prospectively collected blood culture broth samples growing Gram-negative bacteria were extracted using commercially available kits to achieve high-quality DNA.

Assessment of genotypes, endosymbionts and clinical characteristics of Acanthamoeba recovered from ocular infection

Introduction

Acanthamoeba is an emerging pathogen, infamous for its resilience against antiprotozoal compounds, disinfectants and harsh environments. It is known to cause keratitis, a sight-threatening, painful and difficult to treat corneal infection which is often reported among contact lens wearers and patients with ocular trauma. Acanthamoeba comprises over 24 species and currently 23 genotypes (T1-T23) have been identified.

Aims

This retrospective study was designed to examine the Acanthamoeba species and genotypes recovered from patients with Acanthamoeba keratitis (AK), determine the presence of endosymbionts in ocular isolates of Acanthamoeba and review the clinical presentations.

Methodology

Thirteen culture-confirmed AK patients treated in a tertiary eye care facility in Hyderabad, India from February to October 2020 were included in this study. The clinical manifestations, medications and visual outcomes of all patients were obtained from medical records. The Acanthamoeba isolates were identified by sequencing the ribosomal nuclear subunit (rns) gene. Acanthamoeba isolates were assessed for the presence of bacterial or fungal endosymbionts using molecular assays, PCR and fluorescence in situ hybridization (FISH).

Results

The mean age of the patients was 33 years (SD ± 17.4; 95% CI 22.5 to 43.5 years). Six (46.2%) cases had AK associated risk factors; four patients had ocular trauma and two were contact lens wearers. A. culbertsoni (6/13, 46.2%) was the most common species, followed by A. polyphaga and A. triangularis. Most of the isolates (12/13) belonged to genotype T4 and one was a T12; three sub-clusters T4A, T4B, and T4F were identified within the T4 genotype. There was no significant association between Acanthamoeba types and clinical outcomes. Eight (61.5%) isolates harboured intracellular bacteria and one contained Malassezia restricta. The presence of intracellular microbes was associated with a higher proportion of stromal infiltrates (88.9%, 8/9), epithelial defect (55.6%, 5/9) and hypopyon (55.6%, 5/9) compared to 50% (2/4), 25% (1/4) and 25% (1/4) AK cases without intracellular microbes, respectively.

Conclusions

Genotype T4 was the predominant isolate in southern India. This is the second report of T12 genotype identified from AK patient in India, which is rarely reported worldwide. The majority of the Acanthamoeba clinical isolates in this study harboured intracellular microbes, which may impact clinical characteristics of AK.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07741-4.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

An investigation into simplifying total RNA extraction with minimal equipment using a low volume, electrokinetically driven microfluidic protocol

Current methods for total RNA extraction are time-consuming and require several hands-on steps and specialized equipment. Microfluidic devices can offer the opportunity to reduce the number of hands-on steps, decrease the volumes of reagents required for purification, and make extraction high throughput. Here, we investigated the translation of a high volume magnetic bead-based total RNA extraction method (from human whole blood) onto a low input volume microfluidic device. Our results first show that RNA integrity is maintained when the reagent volumes are scaled down by a factor of 22 and the wash buffers are combined 1:1. With our microfluidic method, the number of wash steps can be reduced from four to one. Thus, the time to complete RNA extraction can be reduced from 2 h to 40 min. These manipulations to the conventional protocol yielded RNA amplifiable within 40 cycles of reverse transcription quantitative PCR (RT-qPCR) when using the microfluidic device to simplify the wash steps. To improve the purification of the RNA during the bead transport through the microchannel, we also investigated the effect of a synergetic application of the electrokinetic flow. Our results show that DNase I and other contaminants surrounding the beads get washed away more effectively via electrophoretic transport. Most notably, RNA adsorption on the beads is strong enough to counter electrophoretically-driven desorption. In all, our work opens new ways to extract high-quality total RNA rapidly and simply from a small quantity of blood, making the process of RNA extraction more accessible.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement, towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

Detection of Enteric Viruses from Wastewater and River Water in Botswana

Waterborne diseases remain a public health concern in developing countries where many lack access to safe water. Water testing mainly uses bacterial indicators to assess water quality, which may not fully indicate the threat from other non-bacterial pathogens like enteric viruses. This study was done to ascertain and establish the viral load, the temporal and spatial distribution of rotavirus A and norovirus (GI and GII) in sewage and river water samples. A total of 45 samples of raw and treated sewage, and surface water, were collected from a sludge activated wastewater treatment plant in Gaborone, and after treatment from the Notwane River, Botswana, over a period of 9 months (February 2016 to October 2016). Viruses were concentrated using polyethylene glycol/NaCl precipitation. Virus detection was performed using real-time polymerase chain reaction (RT-PCR). Rotavirus A was the most prevalent (84.4% positive samples), followed by Norovirus GI (48.9% positive samples), and Norovirus GII 46.7% positive samples). Detected viral loads went up to 10⁴ genome copies per liter (copies/L) for all the viruses. The enteric viruses were detected in all the study sites with highest detection from site S1 (inlet). There was no significant association between physicochemical parameters and viral loads, except for pH which showed significant relationship with rotavirus and norovirus GII (p ≤ 0.05). This is the first study in Botswana to highlight the occurrence and quantification of the enteric viruses in treated and untreated wastewater, as well as surface water.

Wastewater-Based Estimation of the Effective Reproductive Number of SARS-CoV-2

BACKGROUND

The effective reproductive number, R e , is a critical indicator to monitor disease dynamics, inform regional and national policies, and estimate the effectiveness of interventions. It describes the average number of new infections caused by a single infectious person through time. To date, R e estimates are based on clinical data such as observed cases, hospitalizations, and/or deaths. These estimates are temporarily biased when clinical testing or reporting strategies change.

OBJECTIVES

We show that the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater can be used to estimate R e in near real time, independent of clinical data and without the associated biases.

METHODS

We collected longitudinal measurements of SARS-CoV-2 RNA in wastewater in Zurich, Switzerland, and San Jose, California, USA. We combined this data with information on the temporal dynamics of shedding (the shedding load distribution) to estimate a time series proportional to the daily COVID-19 infection incidence. We estimated a wastewater-based R e from this incidence.

RESULTS

The method to estimate R e from wastewater worked robustly on data from two different countries and two wastewater matrices. The resulting estimates were as similar to the R e estimates from case report data as R e estimates based on observed cases, hospitalizations, and deaths are among each other. We further provide details on the effect of sampling frequency and the shedding load distribution on the ability to infer R e .

DISCUSSION

To our knowledge, this is the first time R e has been estimated from wastewater. This method provides a low-cost, rapid, and independent way to inform SARS-CoV-2 monitoring during the ongoing pandemic and is applicable to future wastewater-based epidemiology targeting other pathogens. https://doi.org/10.1289/EHP10050.

Evaluation of viral load in patients with Ebola virus disease in Liberia: a retrospective observational study

Background

Viral load in patients with Ebola virus disease affects case fatality rate and is an important parameter used for diagnostic cutoffs, stratification in randomised controlled trials, and epidemiological studies. However, viral load in Ebola virus disease is currently estimated using numerous different assays and protocols that were not developed or validated for this purpose. Here, our aim was to conduct a laboratory-based re-evaluation of the viral loads of a large cohort of Liberian patients with Ebola virus disease and analyse these data in the broader context of the west Africa epidemic.

Methods

In this retrospective observational study, whole blood samples from patients at the Eternal Love Winning Africa Ebola treatment unit (Monrovia, Liberia) were re-extracted with an optimised protocol and analysed by droplet digital PCR (ddPCR) using a novel semi-strand specific assay to measure viral load. To allow for more direct comparisons, the ddPCR viral loads were also back-calculated to cycle threshold (C_t) values. The new viral load data were then compared with the C_t values from the original diagnostic quantitative RT-PCR (qRT-PCR) testing to identify differing trends and discrepancies.

Findings

Between Aug 28 and Dec 18, 2014, 727 whole blood samples from 528 individuals were collected. 463 (64%) were first-draw samples and 409 (56%) were from patients positive for Ebola virus (EBOV), species Zaire ebolavirus. Of the 307 first-draw EBOV-positive samples, 127 (41%) were from survivors and 180 (59%) were from non-survivors; 155 (50%) were women, 145 (47%) were men, and seven (2%) were not recorded, and the mean age was 29·3 (SD 15·0) years for women and 31·8 (SD 14·8) years for men. Survivors had significantly lower mean viral loads at presentation than non-survivors in both the reanalysed dataset (5·61 [95% CI 5·34–5·87] vs 7·19 [6·99–7·38] log₁₀ EBOV RNA copies per mL; p<0·0001) and diagnostic dataset (C_t value 28·72 [27·97–29·47] vs 26·26 [25·72–26·81]; p<0·0001). However, the prognostic capacity of viral load increased with the reanalysed dataset (odds ratio [OR] of death 8·06 [95% CI 4·81–13·53], p<0·0001 for viral loads above 6·71 log₁₀ EBOV RNA copies per mL vs OR of death 2·02 [1·27–3·20], p=0·0028 for C_t values below 27·37). Diagnostic qRT-PCR significantly (p<0·0001) underestimated viral load in both survivors and non-survivors (difference in diagnostic C_t value minus laboratory C_t value of 1·79 [95% CI 1·16–2·43] for survivors and 5·15 [4·43–5·87] for non-survivors). Six samples that were reported negative by diagnostic testing were found to be positive upon reanalysis and had high viral loads.

Interpretation

Inaccurate viral load estimation from diagnostic C_t values is probably multifactorial; however, unaddressed PCR inhibition from tissue damage in patients with fulminant Ebola virus disease could largely account for the discrepancies observed in our study. Testing protocols for Ebola virus disease require further standardisation and validation to produce accurate viral load estimates, minimise false negatives, and allow for reliable epidemiological investigation.

Wastewater-Based Estimation of the Effective Reproductive Number of SARS-CoV-2

BACKGROUND

The effective reproductive number, Re, is a critical indicator to monitor disease dynamics, inform regional and national policies, and estimate the effectiveness of interventions. It describes the average number of new infections caused by a single infectious person through time. To date, Re estimates are based on clinical data such as observed cases, hospitalizations, and/or deaths. These estimates are temporarily biased when clinical testing or reporting strategies change.

OBJECTIVES

We show that the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater can be used to estimate Re in near real time, independent of clinical data and without the associated biases.

METHODS

We collected longitudinal measurements of SARS-CoV-2 RNA in wastewater in Zurich, Switzerland, and San Jose, California, USA. We combined this data with information on the temporal dynamics of shedding (the shedding load distribution) to estimate a time series proportional to the daily COVID-19 infection incidence. We estimated a wastewater-based Re from this incidence.

RESULTS

The method to estimate Re from wastewater worked robustly on data from two different countries and two wastewater matrices. The resulting estimates were as similar to the Re estimates from case report data as Re estimates based on observed cases, hospitalizations, and deaths are among each other. We further provide details on the effect of sampling frequency and the shedding load distribution on the ability to infer Re.

DISCUSSION

To our knowledge, this is the first time Re has been estimated from wastewater. This method provides a low-cost, rapid, and independent way to inform SARS-CoV-2 monitoring during the ongoing pandemic and is applicable to future wastewater-based epidemiology targeting other pathogens. https://doi.org/10.1289/EHP10050.

Intra-Laboratory Evaluation of DNA Extraction Methods and Assessment of a Droplet Digital PCR for the Detection of Xanthomonas citri pv. citri on Different Citrus Species

Xanthomonas citri pv. citri (Xcc) and X. citri pv. aurantifolii (Xca), causal agents of citrus bacterial canker, are both regulated by the European Union to prevent their introduction. Xcc is responsible for severe outbreaks of citrus production worldwide, therefore, a prompt and reliable detection is advisable for the early detection of this bacterium either in symptomatic or asymptomatic plant material. The current EPPO (European and Mediterranean Plant Protection Organization) diagnostic protocol, PM 7/44(1), includes several diagnostic tests even if new assays have been developed in the latter years for which validation data are needed. Recently, a test performance study was organized within the Valitest EU Project to validate Xcc diagnostic methods and provide evidence on the most reliable assays; however, the influence of DNA extraction methods (DEM) on the reliability of the detection has never been assessed. In this study we evaluate four different DEM, by following two different approaches: (i) a comparison by real-time PCR standard curves of bacterial DNA versus bacterial DNA added to plant DNA (lemon, leaves and fruit; orange fruit); and (ii) the evaluation of performance criteria of spiked samples (plant extract added with ten-fold diluted bacterial suspensions at known concentrations). Droplet digital PCR is developed and compared with real-time PCR, as the detection method.

Inferring transmission fitness advantage of SARS-CoV-2 variants of concern from wastewater samples using digital PCR, Switzerland, December 2020 through March 2021

BackgroundThroughout the COVID-19 pandemic, SARS-CoV-2 genetic variants of concern (VOCs) have repeatedly and independently arisen. VOCs are characterised by increased transmissibility, increased virulence or reduced neutralisation by antibodies obtained from prior infection or vaccination. Tracking the introduction and transmission of VOCs relies on sequencing, typically whole genome sequencing of clinical samples. Wastewater surveillance is increasingly used to track the introduction and spread of SARS-CoV-2 variants through sequencing approaches.AimHere, we adapt and apply a rapid, high-throughput method for detection and quantification of the relative frequency of two deletions characteristic of the Alpha, Beta, and Gamma VOCs in wastewater.MethodsWe developed drop-off RT-dPCR assays and an associated statistical approach implemented in the R package WWdPCR to analyse temporal dynamics of SARS-CoV-2 signature mutations (spike Δ69-70 and ORF1a Δ3675-3677) in wastewater and quantify transmission fitness advantage of the Alpha VOC.ResultsBased on analysis of Zurich wastewater samples, the estimated transmission fitness advantage of SARS-CoV-2 Alpha based on the spike Δ69-70 was 0.34 (95% confidence interval (CI): 0.30-0.39) and based on ORF1a Δ3675-3677 was 0.53 (95% CI: 0.49-0.57), aligning with the transmission fitness advantage of Alpha estimated by clinical sample sequencing in the surrounding canton of 0.49 (95% CI: 0.38-0.61).ConclusionDigital PCR assays targeting signature mutations in wastewater offer near real-time monitoring of SARS-CoV-2 VOCs and potentially earlier detection and inference on transmission fitness advantage than clinical sequencing.

Development of a droplet digital polymerase chain reaction tool for the detection of Toxoplasma gondii in meat samples

Toxoplasmosis is a zoonotic disease caused by the protozoan parasite Toxoplasma gondii. Infection in humans has usually been related to the consumption of raw, undercooked or cured meat. The aim of this study was to develop a droplet digital polymerase chain reaction (ddPCR)-based assay for the detection and quantification of T. gondii in meat samples. To optimize the ddPCR, T.gondii reference DNA aliquots at five known concentrations: 8000 cg/µl, 800 cg/µl, 80 cg/µl, 8 cg/µl were used. Moreover, results obtained by ddPCR and quantitative PCR (qPCR) were compared using 80 known samples (40 positive and 40 negative), as well as 171 unknown diaphragm tissue samples collected at slaughterhouses. The ddPCR showed a sensitivity of 97.5% and a specificity of 100%, with a detection limit of 8 genomic copy/µl of T. gondii. A nearly perfect agreement (κ = 0.85) was found between results obtained by ddPCR and qPCR for both positive and negative known samples analysed. On the 171 diaphragm tissue samples from field, 7.6% resulted positive by ddPCR and only 1.2% by qPCR. Therefore, this innovative method could be very useful for the detection of T. gondii in meat samples, aiming to prevent human infections.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement, towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

Circulating microRNA-197-3p as a potential biomarker for asbestos exposure

Asbestos is considered the main cause of diseases in workers exposed to this mineral in the workplace as well as an environmental pollutant. The association between asbestos and the onset of different diseases has been reported, but asbestos exposure specific biomarkers are not known. MicroRNAs (miRNAs) are small, single-strand, non-coding RNAs, with potential value as diagnostic, prognostic, and predictive markers in liquid biopsies. Sera collected from workers ex-exposed to asbestos (WEA) fibers were compared with sera from healthy subjects (HS) of similar age, as liquid biopsies. The expression of the circulating miRNA 197-3p was investigated employing two different highly analytical PCR methods, i.e. RT-qPCR and ddPCR. MiR-197-3p levels were tested in sera from WEA compared to HS. MiR-197-3p tested dysregulated in sera from WEA (n = 75) compared to HS (n = 62). Indeed, miR-197-3p was found to be 2.6 times down-regulated in WEA vs. HS (p = 0.0001***). In addition, an inverse correlation was detected between miR-197-3p expression level and cumulative asbestos exposure, being this miRNA down-regulated 2.1 times in WEA, with high cumulative asbestos exposure, compared to WEA with low exposure (p = 0.0303*). Circulating miR-197-3p, found to be down regulated in sera from WEA, is proposed as a new potential biomarker of asbestos exposure.

High-Throughput and Accurate Determination of Transgene Copy Number and Zygosity in Transgenic Maize: From DNA Extraction to Data Analysis

It is vital to develop high-throughput methods to determine transgene copy numbers initially and zygosity during subsequent breeding. In this study, the target sequence of the previously reported endogenous reference gene hmg was analyzed using 633 maize inbred lines, and two SNPs were observed. These SNPs significantly increased the PCR efficiency, while the newly developed hmg gene assay (hmg-taq-F2/R2) excluding these SNPs reduced the efficiency into normal ranges. The TaqMan amplification efficiency of bar and hmg with newly developed primers was calculated as 0.993 and 1.000, respectively. The inter-assay coefficient of variation (CV) values for the bar and hmg genes varied from 1.18 to 2.94%. The copy numbers of the transgene bar using new TaqMan assays were identical to those using dPCR. Significantly, the precision of one repetition reached 96.7% of that of three repetitions of single-copy plants analyzed by simple random sampling, and the actual accuracy reached 95.8%, confirmed by T₁ and T₂ progeny. With the high-throughput DNA extraction and automated data analysis procedures developed in this study, nearly 2700 samples could be analyzed within eight hours by two persons. The combined results suggested that the new hmg gene assay developed here could be a universal maize reference gene system, and the new assay has high throughput and high accuracy for large-scale screening of maize varieties around the world.

Biosynthesis of Poly-ß-Hydroxybutyrate (PHB) from Different Bacterial Strains Grown on Alternative Cheap Carbon Sources

Thirty bacterial isolates were tested on three different media for Poly-ß-hydroxybutyrate (PHB) production. The best bacterial isolates for producing PHB were screened and identified based on molecular biology; then, using three different alternative carbon sources (dried whey, sugar beet molasses and date molasses), physical properties were evaluated by Infrared (IR) spectrometry and Gas chromatography–mass spectrometry (GC-MS/MS) analysis. Our results showed that the best isolates identified based on molecular biology were Bacillus paramycoides MCCC 1A04098, Azotobacter salinestris NBRC 102611 and Brevundimonas naejangsanensis BIO-TAS2-2. The addition of sugar beet molasses to the medium of A. salinestris increased the cell dry weight (CDW), PHB concentration, PHB% and conversion coefficient (4.97 g/L, 1.56 g/L, 31.38% and 23.92%, respectively). The correlation coefficient values between PHB g/L and CDW g/L varied between very strong and moderate positive correlation. IR of the produced PHB from B. paramycoides and A. salinestris showed similar bands which confirmed the presence of PHB; however, B. naejangsanensis showed weak bands, indicating lower PHB concentration. The chemical composition obtained showed that the GC-MS of the PHB extracted represents 2, 4-ditert-butylphenol for B. paramycoides and isopropyl ester of 2-butenoic acid for both of A. salinestris and Brevundimonas naejangsanensis. Therefore, PHB produced by microorganisms can be considered a biodegradable polyester, and represents a promising technique for the development of eco-friendly and fully biodegradable plastics.

Advances and insights in the diagnosis of viral infections

Viral infections are the most common among diseases that globally require around 60 percent of medical care. However, in the heat of the pandemic, there was a lack of medical equipment and inpatient facilities to provide all patients with viral infections. The detection of viral infections is possible in three general ways such as (i) direct virus detection, which is performed immediately 1-3 days after the infection, (ii) determination of antibodies against some virus proteins mainly observed during/after virus incubation period, (iii) detection of virus-induced disease when specific tissue changes in the organism. This review surveys some global pandemics from 1889 to 2020, virus types, which induced these pandemics, and symptoms of some viral diseases. Non-analytical methods such as radiology and microscopy also are overviewed. This review overlooks molecular analysis methods such as nucleic acid amplification, antibody-antigen complex determination, CRISPR-Cas system-based viral genome determination methods. Methods widely used in the certificated diagnostic laboratory for SARS-CoV-2, Influenza A, B, C, HIV, and other viruses during a viral pandemic are outlined. A comprehensive overview of molecular analytical methods has shown that the assay's sensitivity, accuracy, and suitability for virus detection depends on the choice of the number of regions in the viral open reading frame (ORF) genome sequence and the validity of the selected analytical method.

Competitiveness of Quantitative Polymerase Chain Reaction (qPCR) and Droplet Digital Polymerase Chain Reaction (ddPCR) Technologies, with a Particular Focus on Detection of Antibiotic Resistance Genes (ARGs)

With fast-growing polymerase chain reaction (PCR) technologies and various application methods, the technique has benefited science and medical fields. While having strengths and limitations on each technology, there are not many studies comparing the efficiency and specificity of PCR technologies. The objective of this review is to summarize a large amount of scattered information on PCR technologies focused on the two majorly used technologies: qPCR (quantitative polymerase chain reaction) and ddPCR (droplet-digital polymerase chain reaction). Here we analyze and compare the two methods for (1) efficiency, (2) range of detection and limitations under different disciplines and gene targets, (3) optimization, and (4) status on antibiotic resistance genes (ARGs) analysis. It has been identified that the range of detection and quantification limit varies depending on the PCR method and the type of sample. Careful optimization of target gene analysis is essential for building robust analysis for both qPCR and ddPCR. In our era where mutation of genes may lead to a pandemic of viral infectious disease or antibiotic resistance-induced health threats, this study hopes to set guidelines for meticulous detection, quantification, and analysis to help future prevention and protection of global health, the economy, and ecosystems.

Real-time qPCR to evaluate bacterial contamination of cosmetic cream and the efficiency of protective ingredients

AIMS

The absence of objectionable micro-organisms in cosmetics and the efficiency of preservatives are still mainly assessed by time-consuming cultivation-based methods. We explored the applicability of real-time quantitative polymerase chain reaction (qPCR) and reported on the behaviour of different bacteria in artificially contaminated creams.

METHODS AND RESULTS

Real-time qPCR on DNA from Burkholderia cepacia, Pluribacter gergoviae, Pseudomonas aeruginosa and Sphingomonas paucimobilis identified specific primer pairs that amplify accurately and efficiently two strains/isolates of each species. Using DNeasy mericon Food Kit, we detected bacterial growth in an inoculated cosmetic cream and persistency of DNA from heat-inactivated bacteria. We were also able to monitor the growth inhibitory effect of caprylyl glycol and EDTA, also showing how different bacterial species interact depending on the presence/absence of these ingredients. Finally, creams supplemented with the protective cosmetic ingredients revealed the various behaviour of five strains/isolates from P. aeruginosa.

CONCLUSIONS

Successfully extracting bacterial DNA from artificially contaminated cosmetic creams, we could perform real-time qPCR to identify and follow the growth of various strains of 4 bacteria species under different conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Real-time qPCR appears as a promising method to detect bacterial contamination in cosmetic creams and/or to monitor growth inhibition by ingredients.

Comparison of Skimmed Milk and Lanthanum Flocculation for Concentration of Pathogenic Viruses in Water

Concentration of viruses in water is necessary for detection and quantification of the viruses present, in order to evaluate microbiological barriers in water treatment plants and detect pathogenic viruses during waterborne outbreaks, but there is currently no standardised procedure. In this study, we implemented a previously described fast and simple lanthanum-based protocol for concentration of norovirus genogroup I (GI), genogroup II (GII) and hepatitis A virus (HAV) in drinking and surface water. We compared the results with those of a widely used skimmed milk flocculation method, followed by nucleic acid extraction and RT-qPCR detection. Three seeding levels, with intended concentrations 5 × 10³, 5 × 10⁴ and 5 × 10⁵ genome copies/10 L, were added to drinking water or surface water. All seed levels were detected with both flocculation methods. Samples extracted with skimmed milk flocculation had on average 1.82, 1.86 and 1.38 times higher measured concentration of norovirus GI, GII and HAV, respectively, than those extracted with lanthanum flocculation, across all seeding levels and water types tested. Mengovirus was used as a positive process control. Mengovirus recovery was higher for skimmed milk (40.7% in drinking water, 26.0% in surface water) than for lanthanum flocculation (24.4% in drinking water, 9.7% in surface water). Together, this indicates that skimmed milk flocculation provides higher viral recovery than lanthanum flocculation. However, lanthanum-based flocculation can be performed much faster than skimmed milk flocculation (1.5 h versus 16 h flocculation time) and thus could be a good alternative for rapid monitoring of viruses in water.

The Environmental Microbiology Minimum Information (EMMI) Guidelines: qPCR and dPCR Quality and Reporting for Environmental Microbiology

Real-time quantitative polymerase chain reaction (qPCR) and digital PCR (dPCR) methods have revolutionized environmental microbiology, yielding quantitative organism-specific data of nucleic acid targets in the environment. Such data are essential for characterizing interactions and processes of microbial communities, assessing microbial contaminants in the environment (water, air, fomites), and developing interventions (water treatment, surface disinfection, air purification) to curb infectious disease transmission. However, our review of recent qPCR and dPCR literature in our field of health-related environmental microbiology showed that many researchers are not reporting necessary and sufficient controls and methods, which would serve to strengthen their study results and conclusions. Here, we describe the application, utility, and interpretation of the suite of controls needed to make high quality qPCR and dPCR measurements of microorganisms in the environment. Our presentation is organized by the discrete steps and operations typical of this measurement process. We propose systematic terminology to minimize ambiguity and aid comparisons among studies. Example schemes for batching and combining controls for efficient work flow are demonstrated. We describe critical reporting elements for enhancing data credibility, and we provide an element checklist in the Supporting Information. Additionally, we present several key principles in metrology as context for laboratories to devise their own quality assurance and quality control reporting framework. Following the EMMI guidelines will improve comparability and reproducibility among qPCR and dPCR studies in environmental microbiology, better inform engineering and public health actions for preventing disease transmission through environmental pathways, and for the most pressing issues in the discipline, focus the weight of evidence in the direction toward solutions.

Robustness of digital PCR and real-time PCR against inhibitors in transgene detection for gene doping control in equestrian sports

Gene doping is a threat to fair competition in sports, both human and equestrian. One method of gene doping is to administer exogenous genetic materials, called transgenes, into the bodies of postnatal humans and horses. Polymerase chain reaction (PCR)-based transgene detection methods such as digital PCR and real-time PCR have been developed for gene doping testing in humans and horses. However, the significance of PCR inhibitors in gene doping testing has not been well evaluated. In this study, we evaluated the effects of PCR inhibitors on transgene detection using digital PCR and real-time PCR against gene doping. Digital PCR amplification was significantly inhibited by high concentrations of proteinase K (more than 0.1 μg/μl), ethylenediaminetetraacetic acid (more than 5 nmol/μl), and heparin (more than 0.05 unit/μl) but not by ethanol or genomic DNA. In addition, phenol affected droplet formation in the digital PCR amplification process. Real-time PCR amplification was inhibited by high concentrations of phenol (more than 1% v/v), proteinase K (more than 0.001 μg/μl), ethylenediaminetetraacetic acid (more than 1 nmol/μl), heparin (more than 0.005 unit/μl), and genomic DNA (more than 51.9 ng/μl) but not by ethanol. Although both PCR systems were inhibited by nearly the same substances, digital PCR was more robust than real-time PCR against the inhibitors. We believe that our findings are important for the development of better methods for transgene detection and prevention of false negative results in gene doping testing.

Use and Misuse of Cq in qPCR Data Analysis and Reporting

In the analysis of quantitative PCR (qPCR) data, the quantification cycle (C_q) indicates the position of the amplification curve with respect to the cycle axis. Because C_q is directly related to the starting concentration of the target, and the difference in C_q values is related to the starting concentration ratio, the only results of qPCR analysis reported are often C_q, ΔC_q or ΔΔC_q values. However, reporting of C_q values ignores the fact that C_q values may differ between runs and machines, and, therefore, cannot be compared between laboratories. Moreover, C_q values are highly dependent on the PCR efficiency, which differs between assays and may differ between samples. Interpreting reported C_q values, assuming a 100% efficient PCR, may lead to assumed gene expression ratios that are 100-fold off. This review describes how differences in quantification threshold setting, PCR efficiency, starting material, PCR artefacts, pipetting errors and sampling variation are at the origin of differences and variability in C_q values and discusses the limits to the interpretation of observed C_q values. These issues can be avoided by calculating efficiency-corrected starting concentrations per reaction. The reporting of gene expression ratios and fold difference between treatments can then easily be based on these starting concentrations.

Direct PCR amplification from saliva sample using non-direct multiplex STR kits for forensic DNA typing

Due to its proficiency to provide the most discriminating results for forensic applications, medical research and anthropological studies, multiplex PCR based STR analysis has been established as the most efficient technique in the forensic DNA analysis. Several multiplex amplification kits based on 4, 5 and 6 dyes chemistry are commercially available and used in forensic DNA typing across the globe. These multiplex PCR systems are routinely used for amplification of multiple STR loci (Autosomal, Y and/or X STR's) in the DNA extracted from various biological samples. In the routine forensic DNA testing, DNA profile obtained is compared with the DNA profile of the reference sample, which takes a certain turnaround time and employs costly lab resources. Successive development in forensic DNA typing have resulted in advent of improved multiplex kits which have reduced the effective analysis time, cost and minimized the number of steps required in comparison to conventional forensic DNA typing. Specialized direct amplification compatible multiplex kits are also available nowadays. These kits are relatively costlier but still require few pre-processing steps, which does not make them worth the hefty cost. Herein, this study, we have used non-direct multiplex STR kits to assess their efficacy for direct amplification. In the present study, 103 saliva samples were directly amplified without any pre-treatment of the samples using thirteen non-direct multiplex kits (4 dyes, 5 dyes and 6 dyes chemistry based) for forensic DNA typing. Here, we report a validated direct PCR amplification protocol from the reference saliva samples by omitting DNA extraction and quantification steps, which resulted in 80% reduction of the turnaround time. The developed protocol is cost effective, time efficient and it does not compromise with the quality of DNA profiles. To the best of our knowledge, this is the first report for direct amplification of DNA with the most commonly used non-direct multiplex STR kits without any pre-treatment of the sample. Complete DNA profiles matching all the essential quality parameters were obtained successfully from all the tested samples.

Fluorometric Paper-Based, Loop-Mediated Isothermal Amplification Devices for Quantitative Point-of-Care Detection of Methicillin-Resistant Staphylococcus aureus (MRSA)

Loop-mediated isothermal amplification (LAMP) has been widely used to detect many infectious diseases. However, minor inconveniences during the steps of adding reaction ingredients and lack of simple color results hinder point-of-care detection. We therefore invented a fluorometric paper-based LAMP by incorporating LAMP reagents, including a biotinylated primer, onto a cellulose membrane paper, with a simple DNA fluorescent dye incubation that demonstrated rapid and accurate results parallel to quantitative polymerase chain reaction (qPCR) methods. This technology allows for instant paper strip detection of methicillin-resistant Staphylococcus aureus (MRSA) in the laboratory and clinical samples. MRSA represents a major public health problem as it can cause infections in different parts of the human body and yet is resistant to commonly used antibiotics. In this study, we optimized LAMP reaction ingredients and incubation conditions following a central composite design (CCD) that yielded the shortest reaction time with high sensitivity. These CCD components and conditions were used to construct the paper-based LAMP reaction by immobilizing the biotinylated primer and the rest of the LAMP reagents to produce the ready-to-use MRSA diagnostic device. Our paper-based LAMP device could detect as low as 10 ag (equivalent to 1 copy) of the MRSA gene mecA within 36-43 min, was evaluated using both laboratory (individual cultures of MRSA and non-MRSA bacteria) and clinical blood samples to be 100% specific and sensitive compared to qPCR results, and had 35 day stability under 25 °C storage. Furthermore, the color readout allows for quantitation of MRSA copies. Hence, this device is applicable for point-of-care MRSA detection.

qPCR and qRT-PCR analysis: Regulatory points to consider when conducting biodistribution and vector shedding studies

Gene and cell therapy fields have experienced remarkable growth during the past decade. Demands for preclinical and clinical safety assessments of these cell and gene therapy test articles (TAs) have effectively increased the necessity for regulated biodistribution, vector shedding, gene expression, and/or pharmacokinetics bioanalysis studies. Guidance documents issued from numerous international regulatory authorities recommend the use of quantitative polymerase chain reaction (qPCR) and/or quantitative reverse transcriptase PCR (qRT-PCR) assays due to their highly sensitive and robust target-specific detection. However, only preclinical biodistribution assay sensitivity is specified in these documents. Criteria such as accuracy, precision, and repeatability are not yet defined. This guidance void has resulted in several conflicting institutional interpretations of essential parameters necessary for the development and validation of robust assays to support safety assessments of gene and cell therapy TAs. There is an urgent need for an ongoing discussion among bioanalytical scientists in this field to generate a "best practice" consensus around preclinical and clinical qPCR/qRT-PCR assay design. With regard to this need, we offer critical points to consider when developing, validating, running sample analysis, and reporting qPCR/qRT-PCR assays.

Multiplex TaqMan Real-Time PCR Assay for Sensitive Detection of Two Weevil Species (Coleoptera: Curculionidae)

Rapid and cost-efficient identification of Naupactus species is becoming a key process for the exportation of citrus fruit from Chile and other countries, considering the quarantine regulations for some species of the cosmopolitan genus Naupactus. This study deals with the development of a fast and sensitive detection protocol for Naupactus cervinus (Coleoptera: Curculionidae) (Boheman) and Naupactus xanthographus (Coleoptera: Curculionidae) (Germar) based on multiplex TaqMan Real-time polymerase chain reaction. Both N. cervinus and N. xanthographus primer and probe sets achieved species-specific detection in a linear range from 1 pg/μl to 1 × 10-6 pg/μl, allowing detection of as few as 160 copies of template DNA. Non-target amplifications were not detected and a panel composed of 480 test samples had 100% coincidence with the respective morphological identification.

Impact of metal ions on PCR inhibition and RT-PCR efficiency

Inhibition of PCR by metal ions can pose a serious challenge in the process of forensic DNA analysis. Samples contaminated with various types of metal ions encountered at crime scenes include swabs from metal surfaces such as bullets, cartridge casings, weapons (including guns and knives), metal wires and surfaces as well as bone samples which contain calcium. The mechanism behind the impact of metal ions on DNA recovery, extraction and subsequent amplification is not fully understood. In this study, we assessed the inhibitory effects of commonly encountered metals on DNA amplification. Of the nine tested metals, zinc, tin, iron(II) and copper were shown to have the strongest inhibitory properties having IC50 values significantly below 1 mM. In the second part of the study, three commercially available DNA polymerases were tested for their susceptibility to metal inhibition. We found that KOD polymerase was the most resistant to metal inhibition when compared with Q5 and Taq polymerase. We also demonstrate how the calcium chelator ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) can be used as an easy and non-destructive method of reversing calcium-induced inhibition of PCR reactions.

Field Verification of an African Swine Fever Virus Loop-Mediated Isothermal Amplification (LAMP) Assay During an Outbreak in Timor-Leste

Recent outbreaks of African swine fever virus (ASFV) have seen the movement of this virus into multiple new regions with devastating impact. Many of these outbreaks are occurring in remote, or resource-limited areas, that do not have access to molecular laboratories. Loop-mediated isothermal amplification (LAMP) is a rapid point of care test that can overcome a range of inhibitors. We outline further development of a real-time ASFV LAMP, including field verification during an outbreak in Timor-Leste. To increase field applicability, the extraction step was removed and an internal amplification control (IAC) was implemented. Assay performance was assessed in six different sample matrices and verified for a range of clinical samples. A LAMP detection limit of 400 copies/rxn was determined based on synthetic positive control spikes. A colourmetric LAMP assay was also assessed on serum samples. Comparison of the LAMP assay to a quantitative polymerase chain reaction (qPCR) was performed on clinical ASFV samples, using both serum and oral/rectal swabs, with a substantial level of agreement observed. The further verification of the ASFV LAMP assay, removal of extraction step, implementation of an IAC and the assessment of a range of sample matrix, further support the use of this assay for rapid in-field detection of ASFV.

Improve sample preparation process for miRNA isolation from the culture cells by using silica fiber membrane

In clinical applications of miRNAs, the purity and quality of the testing samples are very critical, especially the obtained tissue sample volume is limited. If the extracted miRNAs are contaminated or different in quality before analysis, it will increase the variance of the analysis result and make the medical information judgment incorrect and cannot be portable. Herein, we improved the commercially extraction kit by realizing the fundamental mechanism and hoped to serve finding optimal procedures for increasing the recovery of miRNAs extracted from cultured cells. In the adsorption process, the factors, like increasing the ethanol concentration or adding Ca²⁺, could influence the RNA adsorption were investigated. For the elution process, the effect caused by raising the elution temperature and raising the pH value of elution buffer was studied. Finally, the conditions for miRNA extraction are optimal modified by using a 65% (v/v) solution of ethanol in the adsorption process, and using TE buffer with the pH value of 8.0 and raising the temperature to 55 °C in the elution. According to the quantified results, the improved extraction kit can promote the recovery of endogenous miR-21 by about 6 times by using the optimal extraction conditions comparing with the miRNeasy Mini Kit.

Technical and Methodological Aspects of Cell-Free Nucleic Acids Analyzes

Analyzes of cell-free nucleic acids (cfNAs) have shown huge potential in many biomedical applications, gradually entering several fields of research and everyday clinical care. Many biological properties of cfNAs can be informative to gain deeper insights into the function of the organism, such as their different types (DNA, RNAs) and subtypes (gDNA, mtDNA, bacterial DNA, miRNAs, etc.), forms (naked or vesicle bound NAs), fragmentation profiles, sequence composition, epigenetic modifications, and many others. On the other hand, the workflows of their analyzes comprise many important steps, from sample collection, storage and transportation, through extraction and laboratory analysis, up to bioinformatic analyzes and statistical evaluations, where each of these steps has the potential to affect the outcome and informational value of the performed analyzes. There are, however, no universal or standard protocols on how to exactly proceed when analyzing different cfNAs for different applications, at least according to our best knowledge. We decided therefore to prepare an overview of the available literature and products commercialized for cfNAs processing, in an attempt to summarize the benefits and limitations of the currently available approaches, devices, consumables, and protocols, together with various factors influencing the workflow, its processes, and outcomes.

The quest for absolute abundance: The use of internal standards for DNA-based community ecology

To characterize microbiomes and other ecological assemblages, ecologists routinely sequence and compare loci that differ among focal taxa. Counts of these sequences convey information regarding the occurrence and relative abundances of taxa, but provide no direct measure of their absolute abundances, due to the technical limitations of the sequencing process. The relative abundances in compositional data are inherently constrained and difficult to interpret. The incorporation of internal standards (ISDs; colloquially referred to as 'spike-ins') into DNA pools can ameliorate the problems posed by relative abundance data and allow absolute abundances to be approximated. Unfortunately, many laboratory and sampling biases cause ISDs to underperform or fail. Here, we discuss how careful deployment of ISDs can avoid these complications and be an integral component of well-designed studies seeking to characterize ecological assemblages via sequencing of DNA.

Genetic assays for guano-based identification of species and sex in bats of the United States and Canada

Bat guano is a noninvasive, data-rich genetic resource. However, the constituent bat DNA is relatively scant, degraded, and complexed with polymerase chain reaction inhibitors. It also is comingled with a rich pool of nontarget DNA from microbes, parasites, and dietary items. We designed and tested new DNA assays for bat species identification (COX1-Bat) and sex identification (XGXYC) for use with guano and other challenging samples. We reviewed previously published assays that can be used with guano samples to obtain the same species and sex data, and attempted to validate these assays for species in which they had not previously been tested. Our results demonstrate that guano-derived DNA can be used successfully to 1) identify nearly all US and Canadian bats at the species level, or to one of three Myotis species clusters, and 2) identify the sex of at least 23 US and Canadian bat species. Our newly developed assays, and validation of previously published assays, for guano-based identification of species and sex in bats, significantly enhance the power of noninvasive sampling and genetic analysis for bat studies, management, and conservation.

Degradation of nuclear and mitochondrial DNA after γ-irradiation and its effect on forensic genotyping

Forensic genotyping can be impeded by γ-irradiation of biological evidence in the event of radiological crime; that is, criminal activity involving radioactive material. Oxidative effects within the mitochondria of living cells elicits greater damage to mitochondrial DNA (mtDNA) than nuclear DNA (nuDNA) at low doses. This study presents a novel approach for the assessment of nuDNA versus mtDNA damage from a comparison of genotype and quantity data, while exploring likely mechanisms for differential damage after high doses of γ-irradiation. Liquid (hydrated) and dried (dehydrated) whole blood samples were exposed to high doses of γ-radiation (1-50 kilogray, kGy). The GlobalFiler PCR Amplification Kit was used to evaluate short tandem repeat (STR) genotyping efficacy and nuDNA degradation; a comparison was made to mtDNA degradation measured using real-time PCR assays. Each assay was normalized before comparison by calculation of integrity indices relative to unirradiated controls. Full STR profiles were attainable up to the highest dose, although DNA degradation was noticeable after 10 and 25 kGy for hydrated and dehydrated blood, respectively. This was manifested by heterozygote imbalance more than allele dropout. Degradation was greater for mtDNA than nuDNA, as well as for hydrated than dehydrated cells, after equivalent doses. Oxidative effects due to water radiolysis and mitochondrial function are dominant mechanisms of differential damage to nuDNA versus mtDNA after high-dose γ-irradiation. While differential DNA damage was reduced by cell desiccation, its persistence after drying indicates innate differences between nuDNA and mtDNA radioresistance and/or continued oxidative effects within the mitochondria.

Optimization of Chelex 100 resin-based extraction of genomic DNA from dried blood spots

Dried blood spots (DBS) are widely utilized as part of universal newborn screening and as a means of transporting samples from field sites. We use DBS from African field sites to assess for rare maternal-fetal cell exchange during pregnancy known as microchimerism. We aimed to develop a protocol to maximize the quantity of high-quality genomic DNA (gDNA) extracted from DBS. The total gDNA yield obtained from control DBS utilizing a Qiagen-based protocol and a Chelex^® 100 resin-based protocol was first compared. Variations of the Chelex^® protocol were subsequently tested to develop an optimized protocol. The gDNA was quantified by qPCR targeting the human beta-globin gene. DNA yield for a given experimental condition was normalized to a Chelex^® control performed on the same day, and the total yields were compared using a Student's t-test. The control Chelex^® protocol yielded 590% more DNA than the QIAamp^® DNA Blood Mini Kit . The absolute efficiency of the control Chelex^® protocol was 54%, compared to an absolute efficiency of 9% for the QIAamp^® DNA Blood Mini Kit. Modification of the Chelex^® protocol to include a second heat precipitation from the same DBS increased the gDNA yield by 29% (P < 0.001). Our optimized protocol including this modification increased the absolute efficiency of extraction to 68%. The gDNA extracted using the Chelex^® protocol was stable through repeated freeze-thaw cycles. In a mock microchimerism experiment, rare donor alleles at a frequency of 10 in 100 000 could be identified in gDNA from DBS extracted using the optimized Chelex^® protocol. Our findings may be of significance for a diverse range of applications that utilize DBS and require high-quality DNA, including newborn screening programs, pathogen and drug resistance screening from remote field sites, forensics, and rare allele detection.

Whole-genome next-generation sequencing and phylogenetic characterization of viral haemorrhagic septicaemia virus in Korea

Whole-genome next-generation sequencing was used to investigate the local evolution of viral haemorrhagic septicaemia virus, a serious pathogen affecting economically important fish such as rainbow trout and turbot in Europe and olive flounder in Asia. Sequence analysis showed that all isolates were genotype IVa, but could be classified further into four subgroups (K1-K4). In addition, genomic regions encompassing the nucleoprotein, phosphoprotein, matrix protein and non-virion protein genes, as well as the seven non-coding regions, were relatively conserved, whereas glycoprotein and RNA-dependent RNA polymerase genes were variable in the coding region. Taken together, the data demonstrate that whole-genome next-generation sequencing may be useful for future surveillance, prevention and control strategies against viral haemorrhagic septicaemia.