Characterization of the Genomic Diversity of Norovirus in Linked Patients Using a Metagenomic Deep Sequencing Approach

An international inter-laboratory study to compare digital PCR with ISO standardized qPCR assays for the detection of norovirus GI and GII in oyster tissue

An optimized digital RT-PCR (RT-dPCR) assay for the detection of human norovirus GI and GII RNA was compared with ISO 15216-conform quantitative real-time RT-PCR (RT-qPCR) assays in an interlaboratory study (ILS) among eight laboratories. A duplex GI/GII RT-dPCR assay, based on the ISO 15216-oligonucleotides, was used on a Bio-Rad QX200 platform by six laboratories. Adapted assays for Qiagen Qiacuity or ThermoFisher QuantStudio 3D were used by one laboratory each. The ILS comprised quantification of norovirus RNA in the absence of matrix and in oyster tissue samples. On average, results of the RT-dPCR assays were very similar to those obtained by RT-qPCR assays. The coefficient of variation (CV%) of norovirus GI results was, however, much lower for RT-dPCR than for RT-qPCR in intra-laboratory replicates (eight runs) and between the eight laboratories. The CV% of norovirus GII results was in the same range for both detection formats. Had in-house prepared dsDNA standards been used, the CV% of norovirus GII could have been in favor of the RT-dPCR assay. The ratio between RT-dPCR and RT-qPCR results varied per laboratory, despite using the distributed RT-qPCR dsDNA standards. The study indicates that the RT-dPCR assay is likely to increase uniformity of quantitative results between laboratories.

Using molecular methods to delineate norovirus outbreaks: a systematic review

Noroviruses are among the major causative agents of human acute gastroenteritis, and the nature of norovirus outbreaks can differ considerably. The number of single-nucleotide polymorphisms (SNPs) between strains is used to assess their relationships. There is currently no universally accepted cutoff value for clustering strains that define an outbreak or linking the individuals involved. This study was conducted to estimate the threshold value of genomic variations among related strains within norovirus outbreaks. We carried out a literature search in the PubMed and Web of Science databases. SNP rates were defined as the number of SNPs/sequence length (bp) × 100%. The Mann-Whitney U-test was used in comparisons of the distribution of SNP rates for different sequence regions, genogroups (GI and GII), transmission routes, and sequencing methods. A total of 25 articles reporting on 108 norovirus outbreaks were included. In 99.1% of the outbreaks, the SNP rates were below 0.50%, and in 89.8%, the SNP rates were under 0.20%. Outbreak strains showed higher SNP rates when the P2 domain was used for sequence analysis (Z = -2.652, p = 0.008) and when an NGS method was used (Z = -3.686, p < 0.001). Outbreaks caused by different norovirus genotypes showed no significant difference in SNP rates. Compared with person-to-person outbreaks, SNP rates were lower in common-source outbreaks, but no significant difference was found when differences in sequencing methods were taken into consideraton. SNP rates under 0.20% and 0.50% could be considered as the rigorous and relaxed threshold, respectively, of strain similarity within a norovirus outbreak. More data are needed to evaluate differences within and between various norovirus outbreaks.

Multiplex MinION sequencing suggests enteric adenovirus F41 genetic diversity comparable to pre-COVID-19 era

Human adenovirus F41 causes acute gastroenteritis in children, and has recently been associated with an apparent increase in paediatric hepatitis of unknown aetiology in the UK, with further cases reported in multiple countries. Relatively little is known about the genetic diversity of adenovirus F41 in UK children; and it is unclear what, if any, impact the COVID-19 pandemic has had on viral diversity in the UK. Methods that allow F41 to be sequenced from clinical samples without the need for viral culture are required to provide the genomic data to address these questions. Therefore, we evaluated an overlapping-amplicon method of sequencing adenovirus genomes from clinical samples using Oxford Nanopore technology. We applied this method to a small sample of adenovirus-species-F-positive extracts collected as part of standard care in the East of England region in January-May 2022. This method produced genomes with >75 % coverage in 13/22 samples and >50 % coverage in 19/22 samples. We identified two F41 lineages present in paediatric patients in the East of England in 2022. Where F41 genomes from paediatric hepatitis cases were available (n=2), these genomes fell within the diversity of F41 from the UK and continental Europe sequenced before and after the 2020-2021 phase of the COVID-19 pandemic. Our analyses suggest that overlapping amplicon sequencing is an appropriate method for generating F41 genomic data from high-virus-load clinical samples, and currently circulating F41 viral lineages were present in the UK and Europe before the COVID-19 pandemic.

Genomic stratification and differential natural selection signatures among human norovirus genogroup II isolates

Noroviruses (NoVs), which are members of the family Caliciviridae, are the most common cause of gastroenteritis in humans. Ten NoV genogroups have been reported so far. Of these, genogroup II (GII) is the most prevalent, and it causes serious infections worldwide. The complete genome sequences of NoV GII isolates from different geographical regions were retrieved from the public database. The model-based clustering approach, implemented in the STRUCTURE resource, was employed for assessment of genetic composition. The MEGA X and IQ Tree tools were used for phylogenetic analysis. Genome-wide natural selection analysis was performed using maximum-likelihood-based methods. The demographic features of NoV GII genome sequences were assessed using the BEAST package. All of the NoV GII sequences initially clustered into two main subpopulations at significant K = 2, where the genotype GII.4 samples clearly split from the rest of the genotypes. This indicates a marked genetic distinction between norovirus GII.4 and non-GII.4 samples. Phylogenetic analysis showed the presence of five distinct subclades for genotype GII.2 and seven subclades for GII.4 samples. Several isolates with admixed ancestry were identified that constituted distinct subclusters in the phylogenetic tree. No continental-specific genetic distinctions were observed among the NoV GII samples. Significant genomic signatures of both positive and negative natural selection were identified across the NoV GII genes. A differential pattern of positive selection signals was inferred between the GII.4 and non-GII.4 genotypes. The demographic analysis revealed an increase in the effective population size of NoV GII during 2009-2010, followed by a rapid fall in 2015.

Viral intra-host evolution in immunocompetent children contributes to human norovirus diversification at the global scale

Norovirus is a major cause of acute gastroenteritis. Human noroviruses present >30 different genotypes, with a single genotype (GII.4) predominating worldwide. Concurrent outbreaks of norovirus are often associated with the emergence of new viruses. While different hypotheses have been presented, the source of new mutations in noroviruses is still unknown. In this study, we applied high-resolution sequencing to determine the intra-host viral diversity presented by noroviruses during the acute and shedding phase of infection in children. Profiling viral intra-host diversification at nearly full genome level indicated that GII.4 viruses presented dynamic intra-host variation, while non-GII.4 viruses presented minimal variation throughout the infection. Notably, the intra-host genetic variation during the shedding phase recapitulates the genetic diversity observed at the global level, particularly those mapping at the VP1 antigenic sites. Thus the intra-host evolution in healthy children explains the source of norovirus mutations that results in diversification at the global scale.

Benchmarking different approaches for Norovirus genome assembly in metagenome samples

BACKGROUND

Genome assembly of viruses with high mutation rates, such as Norovirus and other RNA viruses, or from metagenome samples, poses a challenge for the scientific community due to the coexistence of several viral quasispecies and strains. Furthermore, there is no standard method for obtaining whole-genome sequences in non-related patients. After polyA RNA isolation and sequencing in eight patients with acute gastroenteritis, we evaluated two de Bruijn graph assemblers (SPAdes and MEGAHIT), combined with four different and common pre-assembly strategies, and compared those yielding whole genome Norovirus contigs.

RESULTS

Reference-genome guided strategies with both host and target virus did not present any advantages compared to the assembly of non-filtered data in the case of SPAdes, and in the case of MEGAHIT, only host genome filtering presented improvements. MEGAHIT performed better than SPAdes in most samples, reaching complete genome sequences in most of them for all the strategies employed. Read binning with CD-HIT improved assembly when paired with different analysis strategies, and more notably in the case of SPAdes.

CONCLUSIONS

Not all metagenome assemblies are equal and the choice in the workflow depends on the species studied and the prior steps to analysis. We may need different approaches even for samples treated equally due to the presence of high intra host variability. We tested and compared different workflows for the accurate assembly of Norovirus genomes and established their assembly capacities for this purpose.

Genomic analysis of human noroviruses using combined Illumina-Nanopore data

Whole-genome sequence analysis of noroviruses is routinely performed by employing a metagenomic approach. While this methodology has several advantages, such as allowing for the examination of co-infection, it has some limitations, such as the requirement of high viral load to achieve full-length or near full-length genomic sequences. In this study, we used a pre-amplification step to obtain full-length genomic amplicons from 39 Canadian GII isolates, followed by deep sequencing on Illumina and Oxford Nanopore platforms. This approach significantly reduced the required viral titre to obtain full-genome coverage. Herein, we compared the coverage and sequences obtained by both platforms and provided an in-depth genomic analysis of the obtained sequences, including the presence of single-nucleotide variants and recombination events.

Prolonged norovirus infections correlate to quasispecies evolution resulting in structural changes of surface-exposed epitopes

In this study, we analyzed norovirus (NoV) evolution in sequential samples of six chronically infected patients. The capsid gene was amplified from stool samples, and deep sequencing was performed. The role of amino acid flexibility in structural changes and ligand binding was studied with molecular dynamics (MD) simulations. Concentrations of capsid-specific antibodies increased in sequential sera. Capsid sequences accumulated mutations during chronic infection, particularly in the surface-exposed antigenic epitopes A, D, and E. The number of quasispecies increased in infections lasting for >1 month. Interestingly, high genetic complexity and distances were followed by ongoing NoV replication, whereas lower genetic complexity and distances preceded cure. MD simulation revealed that surface-exposed amino acid substitutions of the P2 domain caused fluctuation of blockade epitopes. In conclusion, the capsid protein accumulates numerous mutations during chronic infection; however, only those on the protein surface change the protein structure substantially and may lead to immune escape.

De novo Sequencing of Novel Mycoviruses From Fusarium sambucinum: An Attempt on Direct RNA Sequencing of Viral dsRNAs

An increasing number of viruses are continuously being found in a wide range of organisms, including fungi. Recent studies have revealed a wide viral diversity in microbes and a potential importance of these viruses in the natural environment. Although virus exploration has been accelerated by short-read, high-throughput sequencing (HTS), and viral de novo sequencing is still challenging because of several biological/molecular features such as micro-diversity and secondary structure of RNA genomes. This study conducted de novo sequencing of multiple double-stranded (ds) RNA (dsRNA) elements that were obtained from fungal viruses infecting two Fusarium sambucinum strains, FA1837 and FA2242, using conventional HTS and long-read direct RNA sequencing (DRS). De novo assembly of the read data from both technologies generated near-entire genomic sequence of the viruses, and the sequence homology search and phylogenetic analysis suggested that these represented novel species of the Hypoviridae, Totiviridae, and Mitoviridae families. However, the DRS-based consensus sequences contained numerous indel errors that differed from the HTS consensus sequences, and these errors hampered accurate open reading frame (ORF) prediction. Although with its present performance, the use of DRS is premature to determine viral genome sequences, the DRS-mediated sequencing shows great potential as a user-friendly platform for a one-shot, whole-genome sequencing of RNA viruses due to its long-reading ability and relative structure-tolerant nature.

High Throughput Sequencing for the Detection and Characterization of RNA Viruses

This review aims to assess and recommend approaches for targeted and agnostic High Throughput Sequencing of RNA viruses in a variety of sample matrices. HTS also referred to as deep sequencing, next generation sequencing and third generation sequencing; has much to offer to the field of environmental virology as its increased sequencing depth circumvents issues with cloning environmental isolates for Sanger sequencing. That said however, it is important to consider the challenges and biases that method choice can impart to sequencing results. Here, methodology choices from RNA extraction, reverse transcription to library preparation are compared based on their impact on the detection or characterization of RNA viruses.

Complete genome characterization of human noroviruses allows comparison of minor alleles during acute and chronic infections

Human noroviruses (HuNoVs) circulate globally, affect all age groups and place a substantial burden upon health services. High genetic diversity leading to antigenic variation plays a significant role in HuNoV epidemiology, driving periodic global emergence of epidemic variants. Studies have suggested that immunocompromised individuals may be a reservoir for such epidemic variants, but studies investigating the diversity and emergence of HuNoV variants in immunocompetent individuals are underrepresented. To address this, we sequenced the genomes of HuNoVs present in samples collected longitudinally from one immunocompetent (acute infection) and one immunocompromised (chronic infection) patient. A broadly reactive HuNoV capture-based method was used to concentrate the virus present in these specimens prior to massively parallel sequencing to recover near complete viral genomes. Using a novel bioinformatics pipeline, we demonstrated that persistent minor alleles were present in both acute and chronic infections, and that minor allele frequencies represented a larger proportion of the population during chronic infection. In acute infection, minor alleles were more evenly spread across the genome, although present at much lower frequencies, and therefore difficult to discern from error. By contrast, in the chronic infection, more minor alleles were present in the minor structural protein. No non-synonymous minor alleles were detected in the major structural protein over the short sampling period of the HuNoV chronic infection, suggesting where immune pressure is variable or non-existent, epidemic variants could emerge over longer periods of infection by random chance.

Application of Next-Generation Sequencing to Reveal How Evolutionary Dynamics of Viral Population Shape Dengue Epidemiology

Dengue viral (DENV) infection results in a wide spectrum of clinical manifestations from asymptomatic, mild fever to severe hemorrhage diseases upon infection. Severe dengue is the leading cause of pediatric deaths and/or hospitalizations, which are a major public health burden in dengue-endemic or hyperendemic countries. Like other RNA viruses, DENV continues to evolve. Adaptive mutations are obscured by the major consensus sequence (so-called wild-type sequences) and can only be identified once they become the dominant viruses in the virus population, a process that can take months or years. Traditional surveillance systems still rely on Sanger consensus sequencing. However, with the recent advancement of high-throughput next-generation sequencing (NGS) technologies, the genome-wide investigation of virus population within-host and between-hosts becomes achievable. Thus, viral population sequencing by NGS can increase our understanding of the changing epidemiology and evolution of viral genomics at the molecular level. This review focuses on the studies within the recent decade utilizing NGS in different experimental and epidemiological settings to understand how the adaptive evolution of dengue variants shapes the dengue epidemic and disease severity through its transmission. We propose three types of studies that can be pursued in the future to enhance our surveillance for epidemic prediction and better medical management.

Evaluation of High-Pressure Processing in Inactivation of the Hepatitis E Virus

Hepatitis E virus (HEV) causes acute hepatitis with approximately 20 million cases per year globally. Based on genetic diversity, HEV is classified into different genotypes, with genotype 3 (HEV-3) being most prevalent in Europe and North America. The transmission of HEV-3 has been shown to be zoonotic and mainly associated with the consumption of raw or undercooked pork products. Herein, we investigated the efficacy of high-pressure processing (HPP) in inactivation of HEV-3 using a cell culture system. HPP has been indicated as a promising non-thermal pathogen inactivation strategy for treatment of certain high-risk food commodities, without any noticeable changes in their nature. For this purpose, we treated HEV-3 in media with different conditions of HPP: 400 MPa for 1 and 5 min, as well as 600 MPa for 1 and 5 min, at ambient temperature. All four HPP treatments of HEV in media were observed to result in a 2-log reduction in HEV load, as determined by the amounts of extracellular HEV RNA produced at 14-day post-infection, using the A549/D3 cell culture system. However, application of the same treatments to artificially contaminated pork pâté resulted in 0.5 log reduction in viral load. These results indicate that the efficacy of HPP treatment in the inactivation of HEV-3 is matrix-dependent, and independent of maximum pressure between 400 and 600 MPa and hold time between 1 and 5 min. Based on the obtained results, although the HPP treatment of pork pâté reduces the HEV-3 load, it might not be sufficient to fully mitigate the risk.

Genotype-Specific Neutralization of Norovirus Is Mediated by Antibodies Against the Protruding Domain of the Major Capsid Protein

Human noroviruses are the most common viral agents of acute gastroenteritis. Recently, human intestinal enteroids were shown to be permissive for norovirus infection. We tested their suitability as a system to study norovirus neutralization. Hyperimmune sera raised against virus-like particles (VLPs) representing different genotypes showed highly specific neutralization activity against GII.4 and GII.6 noroviruses. Carbohydrate blocking assays and neutralization exhibited similar patterns in antibody responses. Notably, sera produced against chimeric VLPs that presented swapped structural shell and protruding (P) domains, from different genotypes showed that neutralization is primarily mediated by antibodies mapping to the P domain of the norovirus capsid protein. This study provides empirical information on the antigenic differences among genotypes as measured by neutralization, which could guide vaccine design.

Evaluation of Bead-Based Assays for the Isolation of Foodborne Viruses from Low-Moisture Foods

ABSTRACT

Foodborne viruses such as norovirus and hepatitis A virus (HAV) are highly transmissible, persistent in the environment, and resistant to many conventional inactivation methods. Foods can become contaminated with these viruses either at the source of harvest or during food handling and processing. Multiple lines of evidence suggest that foodborne viruses can survive desiccation and dry conditions. Several foodborne virus outbreaks have been linked to low-moisture foods (LMFs), indicating that these foods can be vehicles of virus transmission. However, the efficiencies of common virus extraction methodologies have not been examined with LMFs. We adapted the International Organization for Standardization (ISO) 15216-1:2017 method for virus recovery for use with chocolate, pistachios, and cornflakes. We also developed a magnetic bead assay for the recovery of HAV from LMFs and used the porcine gastric mucin-coated magnetic beads (PGM-MBs) to extract norovirus surrogates, feline calicivirus (FCV), and murine norovirus (MNV) from the same LMFs. The efficiency of virus recovery using the bead-based assay was then compared with that of the ISO 15216-1:2017 method. In chocolate and pistachios, the recovery rates with the PGM-MB method were 5.6- and 21.3-fold higher, respectively, for FCV and 1.65- and 18-fold higher, respectively, for MNV than those with the ISO 15216-1:2017 method. However, the PGM-MB method failed to recover MNV and FCV from cornflakes. The recovery rates for HAV in chocolate, pistachios, and corn flakes with the magnetic bead method were 11.5-, 3-, and 5.6-fold higher, respectively, than those with the ISO 15216-1:2017 method. Thus, depending upon the food matrix and the target virus, the bead-based assays can be used to efficiently and rapidly extract viruses from LMFs.

HIGHLIGHTS

Outbreaks, occurrence, and control of norovirus and hepatitis a virus contamination in berries: A review

Foodborne enteric viruses, in particular HuNoV and HAV, are the most common cause of the berry-linked viral diseases, and outbreaks around the world, and have become an important concern for health authorities. Despite the increased importance of berry fruits as a vehicle for foodborne viruses, there is limited information concerning the fate of foodborne viruses in the berry supply chain from farm to consumer. A comprehensive understanding of berry-associated viral outbreaks - with a focus on contamination sources, persistence, survival, and the effects of current postharvest and processing interventions and practices - is essential for the development of effective preventative strategies to reduce risk of illness. The purpose of this paper is twofold; (i) to critically review the published literature on the current state of knowledge regarding berry-associated foodborne viral outbreaks and the efficiency of berry processing practices and (ii) to identify and prioritize research gaps regarding practical and effective mechanism to reduce viral contamination of berries. The review found that fecally infected food handlers were the predominant source of preharvest and postharvest pathogenic viral contamination. Current industrial practices applied to fresh and frozen berries demonstrated limited efficacy for reducing the viral load. While maintaining best practice personal and environmental hygiene is a key intervention, the optimization of processing parameters (i.e., freezing, frozen storage, and washing) and/or development of alternative processing technologies to induce sufficient viral inactivation in berries along with retaining sensory and nutritional quality, is also an important direction for further research.

Foodborne viral outbreaks associated with frozen produce

Over the past decade, frozen fruits have been a major vehicle of foodborne illnesses mainly attributed to norovirus (NoV) and hepatitis A virus (HAV) infections. Fresh produce may acquire viral contamination by direct contact with contaminated surface, water or hands, and is then frozen without undergoing proper decontamination. Due to their structural integrity, foodborne viruses are able to withstand hostile conditions such as desiccation and freezing, and endure for a long period of time without losing their infectivity. Additionally, these foods are often consumed raw or undercooked, which increases the risk of infection. Herein, we searched published literature and databases of reported outbreaks as well as the databases of news articles for the viral outbreaks associated with the consumption of frozen produce between January 2008 and December 2018; recorded the worldwide distribution of these outbreaks; and analysed the implication of consumption of different types of contaminated frozen food. In addition, we have briefly discussed the factors that contribute to an increased risk of foodborne viral infection following the consumption of frozen produce. Our results revealed that frozen fruits, especially berries and pomegranate arils, contributed to the majority of the outbreaks, and that most outbreaks were reported in industrialised countries.

Advances in Diagnostic Approaches for Viral Etiologies of Diarrhea: From the Lab to the Field

The applications of correct diagnostic approaches play a decisive role in timely containment of infectious diseases spread and mitigation of public health risks. Nevertheless, there is a need to update the diagnostics regularly to capture the new, emergent, and highly divergent viruses. Acute gastroenteritis of viral origin has been identified as a significant cause of mortality across the globe, with the more serious consequences seen at the extremes of age groups (young and elderly) and immune-compromised individuals. Therefore, significant advancements and efforts have been put in the development of enteric virus diagnostics to meet the WHO ASSURED criteria as a benchmark over the years. The Enzyme-Linked Immunosorbent (ELISA) and Polymerase Chain Reaction (PCR) are the basic assays that provided the platform for development of several efficient diagnostics such as real-time RT-PCR, loop-mediated isothermal amplification (LAMP), polymerase spiral reaction (PSR), biosensors, microarrays and next generation sequencing. Herein, we describe and discuss the applications of these advanced technologies in context to enteric virus detection by delineating their features, advantages and limitations.

Analysis of GII.P7 and GII.6 noroviruses circulating in Italy during 2011-2016 reveals a replacement of lineages and complex recombination history

Noroviruses are important human enteric pathogens and monitoring their genetic diversity is important for epidemiological surveillance, vaccine development, and understanding of RNA viruses evolution. Epidemiological investigations have revealed that genogroup II, genotype 6 noroviruses (GII.6) are common agents of gastroenteritis. Upon sequencing of the ORF2 (encoding the viral capsid), GII.6 viruses have been distinguished into three variants. Sentinel hospital-based surveillance in Italy revealed that GII.6 noroviruses were the second most common capsid genotype in 2015, mostly in association with a GII.P7 ORF1 (encoding the viral polymerase). Upon molecular characterization of the ORF1 and ORF2, the GII.P7_GII.6 epidemic viruses circulating in 2014-2015 (variant GII.6b) were different from those that circulated sporadically in 2011-2013 (variant GII.6a). Analysis of the ORF1 (GII.P7) and ORF2 (GII.6) sequences available in the databases unveiled marked genetic diversity and peculiarities in the phylogenetic segregation patterns, suggesting multiple recombination events. Phylogenetic analyses suggest that recent GII.P7_GII.6b viruses were circulating as early as 2008, and formed a genetically homogenous group that emerged globally.

Applied shotgun metagenomics approach for the genetic characterization of dengue viruses

Dengue virus (DENV), an arthropod-borne virus, has rapidly spread in recent years. DENV diagnosis is performed through virus serology, isolation or molecular detection, while genotyping is usually done through Sanger sequencing of the envelope gene. This study aimed to optimize the use of shotgun metagenomics and subsequent bioinformatics analysis to detect and type DENV directly from clinical samples without targeted amplification. Additionally, presence of DENV quasispecies (intra-host variation) was revealed by detecting single nucleotide variants. Viral RNA was isolated with or without DNase-I treatment from 17 DENV (1-4) positive blood samples. cDNA libraries were generated using either a combination of the NEBNext® RNA to synthesize cDNA followed by Nextera XT DNA library preparation, or the TruSeq RNA V2 (TS) library preparation kit. Libraries were sequenced using both the MiSeq and NextSeq. Bioinformatic analysis showed complete ORFs for all samples by all approaches, but longer contigs and higher sequencing depths were obtained with the TS kit. No differences were observed between MiSeq and NextSeq sequencing. Detection of multiple DENV serotypes in a single sample was feasible. Finally, results were obtained within three days with associated reagents costs between €130-170/sample. Therefore, shotgun metagenomics is suitable for identification and typing of DENV in a clinical setting.

Genome and pan-genome analysis to classify emerging bacteria

Background

In the recent years, genomic and pan-genomic studies have become increasingly important. Culturomics allows to study human microbiota through the use of different culture conditions, coupled with a method of rapid identification by MALDI-TOF, or 16S rRNA. Bacterial taxonomy is undergoing many changes as a consequence. With the help of pan-genomic analyses, species can be redefined, and new species definitions generated.

Results

Genomics, coupled with culturomics, has led to the discovery of many novel bacterial species or genera, including Akkermansia muciniphila and Microvirga massiliensis. Using the genome to define species has been applied within the genus Klebsiella. A discontinuity or an abrupt break in the core/pan-genome ratio can uncover novel species.

Conclusions

Applying genomic and pan-genomic analyses to the reclassification of other bacterial species or genera will be important in the future of medical microbiology. The pan-genome is one of many new innovative tools in bacterial taxonomy.

Reviewers

This article was reviewed by William Martin, Eric Bapteste and James Mcinerney.

Open peer review

Reviewed by William Martin, Eric Bapteste and James Mcinerney.

Genetic characterization of norovirus GII.4 variants circulating in Canada using a metagenomic technique

BACKGROUND

Human norovirus is the leading cause of viral gastroenteritis globally, and the GII.4 has been the most predominant genotype for decades. This genotype has numerous variants that have caused repeated epidemics worldwide. However, the molecular evolutionary signatures among the GII.4 variants have not been elucidated throughout the viral genome.

METHOD

A metagenomic, next-generation sequencing method, based on Illumina RNA-Seq, was applied to determine norovirus sequences from clinical samples.

RESULTS

Herein, the obtained deep-sequencing data was employed to analyze full-genomic sequences from GII.4 variants prevailing in Canada from 2012 to 2016. Phylogenetic analysis demonstrated that the majority of these sequences belong to New Orleans 2009 and Sydney 2012 strains, and a recombinant sequence was also identified. Genome-wide similarity analyses implied that while the capsid gene is highly diverse among the isolates, the viral protease and polymerase genes remain relatively conserved. Numerous amino acid substitutions were observed at each putative antigenic epitope of the VP1 protein, whereas few amino acid changes were identified in the polymerase protein. Co-infection with other enteric RNA viruses was investigated and the astrovirus genome was identified in one of the samples.

CONCLUSIONS

Overall this study demonstrated the application of whole genome sequencing as an important tool in molecular characterization of noroviruses.

Critical steps in clinical shotgun metagenomics for the concomitant detection and typing of microbial pathogens

High throughput sequencing has been proposed as a one-stop solution for diagnostics and molecular typing directly from patient samples, allowing timely and appropriate implementation of measures for treatment, infection prevention and control. However, it is unclear how the variety of available methods impacts the end results. We applied shotgun metagenomics on diverse types of patient samples using three different methods to deplete human DNA prior to DNA extraction. Libraries were prepared and sequenced with Illumina chemistry. Data was analyzed using methods likely to be available in clinical microbiology laboratories using genomics. The results of microbial identification were compared to standard culture-based microbiological methods. On average, 75% of the reads corresponded to human DNA, being a major determinant in the analysis outcome. None of the kits was clearly superior suggesting that the initial ratio between host and microbial DNA or other sample characteristics were the major determinants of the proportion of microbial reads. Most pathogens identified by culture were also identified through metagenomics, but substantial differences were noted between the taxonomic classification tools. In two cases the high number of human reads resulted in insufficient sequencing depth of bacterial DNA for identification. In three samples, we could infer the probable multilocus sequence type of the most abundant species. The tools and databases used for taxonomic classification and antimicrobial resistance identification had a key impact on the results, recommending that efforts need to be aimed at standardization of the analysis methods if metagenomics is to be used routinely in clinical microbiology.

Characterization of intra- and inter-host norovirus P2 genetic variability in linked individuals by amplicon sequencing

Noroviruses are the main cause of epidemics of acute gastroenteritis at a global scale. Although chronically infected immunocompromised individuals are regarded as potential reservoirs for the emergence of new viral variants, viral quasispecies distribution and evolution patterns in acute symptomatic and asymptomatic infections has not been extensively studied. Amplicons of 450 nts from the P2 coding capsid domain were studied using next-generation sequencing (454/GS-Junior) platform. Inter-host diversity between symptomatic and asymptomatic acutely infected individuals linked to the same outbreak as well as their viral intra-host diversity over time were characterized. With an average of 2848 reads per sample and a cutoff frequency of 0.1%, minor variant haplotypes were detected in 5 out of 8 specimens. Transmitted variants could not be confirmed in all infected individuals in one outbreak. The observed initial intra-host viral diversity in asymptomatically infected subjects was higher than in symptomatic ones. Viral quasispecies evolution over time within individuals was host-specific, with an average of 2.8 nt changes per day (0.0062 changes per nucleotide per day) in a given symptomatic case. Nucleotide polymorphisms were detected in 28 out of 450 analyzed nucleotide positions, 32.14% of which were synonymous and 67.86% were non-synonymous. Most observed amino acid changes emerged at or near blockade epitopes A, B, D and E. Our results suggest that acutely infected individuals, even in the absence of symptoms, which go underreported and may enhance transmission, may contribute to norovirus genetic variability and evolution.

Metagenomics: The Next Culture-Independent Game Changer

A trend towards the abandonment of obtaining pure culture isolates in frontline laboratories is at a crossroads with the ability of public health agencies to perform their basic mandate of foodborne disease surveillance and response. The implementation of culture-independent diagnostic tests (CIDTs) including nucleic acid and antigen-based assays for acute gastroenteritis is leaving public health agencies without laboratory evidence to link clinical cases to each other and to food or environmental substances. This limits the efficacy of public health epidemiology and surveillance as well as outbreak detection and investigation. Foodborne outbreaks have the potential to remain undetected or have insufficient evidence to support source attribution and may inadvertently increase the incidence of foodborne diseases. Next-generation sequencing of pure culture isolates in clinical microbiology laboratories has the potential to revolutionize the fields of food safety and public health. Metagenomics and other 'omics' disciplines could provide the solution to a cultureless future in clinical microbiology, food safety and public health. Data mining of information obtained from metagenomics assays can be particularly useful for the identification of clinical causative agents or foodborne contamination, detection of AMR and/or virulence factors, in addition to providing high-resolution subtyping data. Thus, metagenomics assays may provide a universal test for clinical diagnostics, foodborne pathogen detection, subtyping and investigation. This information has the potential to reform the field of enteric disease diagnostics and surveillance and also infectious diseases as a whole. The aim of this review will be to present the current state of CIDTs in diagnostic and public health laboratories as they relate to foodborne illness and food safety. Moreover, we will also discuss the diagnostic and subtyping utility and concomitant bias limitations of metagenomics and comparable detection techniques in clinical microbiology, food and public health laboratories. Early advances in the discipline of metagenomics, however, have indicated noteworthy challenges. Through forthcoming improvements in sequencing technology and analytical pipelines among others, we anticipate that within the next decade, detection and characterization of pathogens via metagenomics-based workflows will be implemented in routine usage in diagnostic and public health laboratories.