Preparation of MS2-based nanoparticles as control and standard materials for the molecular detection of dengue virus serotypes

One-plasmid double-expression system for preparation of MS2 virus-like particles packaging SARS-CoV-2 RNA

COVID-19 is a disease caused by a virus named SARS-CoV-2. SARS-CoV-2 is a single-stranded positive-sense RNA virus. Reverse transcription quantitative PCR (RT-qPCR) assays are the gold standard molecular test for detection of RNA viruses. The aim of this study was to construct an RNA-positive control based on MS2 phage-like particles (MS2 VLPs) to detect SARS-CoV-2 RNA. pCDFDuet-1 was used as a one-plasmid double-expression system to construct MS2 VLPs containing ssRNA of SARS-CoV-2. The sequence encoding one copy of maturase, His-tag and coat protein dimer was cloned and inserted into MCS1 of the plasmid; the fragment encoding protein N and ORF1ab from SARS-CoV-2 was cloned and inserted into MCS2. The prepared plasmid was transformed into Escherichia coli strain BL2 (DE3), and expression of the construct was induced by 1 mM isopropyl-L-thio-D-galactopyranoside (IPTG) at 30°C for 12 hours. MS2 VLPs were purified and collected with Ni-NTA affinity chromatography columns. The size and shape of the MS2 VLPs were verified by transmission electron microscopy, and the stability of MS2 VLP packaged RNA was evaluated by treatment with RNase A. Effects of storage temperature and buffer on MS2 VLP stability were also investigated. The results showed that SARS-CoV-2 MS2 VLPs could be successfully produced by this one-plasmid double-expression system. MS2 VLPs showed high stability and may be used as a positive control in molecular diagnosis of COVID-19.

External quality assessment of molecular testing of 9 viral encephalitis-related viruses in China

BACKGROUND

Eastern equine encephalitis virus (EEEV), Western equine encephalitis virus (WEEV), Venezuelan equine encephalitis virus (VEEV), Hendra virus (HeV), Nipah virus (NiV), Yellow fever virus (YFV), West Nile virus (WNV), Saint Louis encephalitis virus (SLEV) and Tick-borne encephalitis virus (TBEV) have been detected in travelers returning to China and potentially pose a serious threat to public health. Real-time reverse transcription polymerase chain reaction (rRT-PCR) plays an important role in the detection of these viruses. Although these viruses are not mainly prevalent in China, occasionally imported cases have been reported with the increase in population mobility and entry-exit activities. Therefore, it is necessary to monitor the ability of major domestic laboratories to detect and identify exotic arbovirus infections in travelers.

METHODS

An external quality assessment program for the molecular detection of EEEV, VEEV, WEEV, SLEV, WNV, YFV, TBEV, HeV and NiV was organized. The assessment panel included 26 negative and positive samples with different concentrations of virus-like particles and distributed to 31 laboratories to evaluate the accuracy of virus detection.

RESULTS

At the laboratory level, 87.5% (7/8, EEEV), 85.7% (12/14, WEEV), 100% (13/13, VEEV), 87.5% (7/8, HeV), 76.5% (13/17, NiV), 92.6% (25/27, YFV), 81.3% (13/16, WNV), 100% (5/5, SLEV) and 75.0% (6/8, TBEV) of the participants were considered "competent". Of all the results, the false-positive and false-negative rates were 0.3% and 0.7%, respectively. The sensitivity of most detection assays (15/17, 88.2%) was more than 90%. In addition, we observed significantly different cycle threshold values when using primer-probe sets in different target regions to detect EEEV and SLEV.

CONCLUSIONS

Most laboratories have reliable virus detection capabilities. However, laboratory testing capabilities need to be improved to avoid cross-contamination and to better manage undetected false-negative samples.

Comparison of Seven Commercial Severe Acute Respiratory Syndrome Coronavirus 2 Nucleic Acid Detection Reagents with Pseudovirus as Quality Control Material

The ongoing pandemic of coronavirus disease 2019 threatens the whole world, which catalyzes a variety of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid test (NAT) kits. To monitor test quality and evaluate NAT kits, quality control materials that best simulate real clinical samples are needed. In this study, the performance of SARS-CoV-2 cell culture supernatant, PCDH-based pseudovirus, and MS2-based pseudovirus as quality control materials was compared. PCDH-based pseudovirus was found to be more similar in characteristics to SARS-CoV-2 particle, and more suitable for evaluating SARS-CoV-2 NAT kits than MS2-based pseudovirus. Proper detection using sensitive and precise NAT kits is essential to guarantee diagnosis. Thus, limit of detection, precision, anti-inference ability, and cross-reactivity of NAT kits from PerkinElmer, Beijing Wantai Biological Pharmacy Enterprise Co, Ltd, Shanghai Kehua Bio-Engineering Co, Ltd, Sansure Biotech Inc., Da An Gene Co, Ltd, Shanghai BioGerm Medical Biotechnology Co, Ltd, and Applied Biological Technologies Co, Ltd, were compared using PCDH-based pseudovirus. For the seven kits evaluated, N gene was more sensitive than ORF1ab gene in most kits, whereas E gene was most sensitive among the three genes in Shanghai Kehua Bio-Engineering Co, Ltd, and Applied Biological Technologies Co, Ltd. PerkinElmer got the lowest limit of detection for N gene at 11.61 copies/mL, and the value was 34.66 copies/mL for ORF1ab gene. All of the kits showed good precision, with CV values less than 5%, as well as acceptable anti-interference ability of 2 mg/L human genomic DNA. No cross-reactivity was observed with other respiratory viruses.