Impact of wet-lab protocols on quality of whole-genome short-read sequences from foodborne microbial pathogens.

For successful elucidation of a food-borne infection chain, the availability of high-quality sequencing data from suspected microbial contaminants is a prerequisite. Commonly, those investigations are a joint effort undertaken by different laboratories and institutes. To analyze the extent of variability introduced by differing wet-lab procedures on the quality of the sequence data we conducted an interlaboratory study, involving four bacterial pathogens, which account for the majority of food-related bacterial infections: Campylobacter spp., Shiga toxin-producing Escherichia coli, Listeria monocytogenes, and Salmonella enterica. The participants, ranging from German federal research institutes, federal state laboratories to universities and companies, were asked to follow their routine in-house protocols for short-read sequencing of 10 cultures and one isolated bacterial DNA per species. Sequence and assembly quality were then analyzed centrally. Variations within isolate samples were detected with SNP and cgMLST calling. Overall, we found that the quality of Illumina raw sequence data was high with little overall variability, with one exception, attributed to a specific library preparation kit. The variability of Ion Torrent data was higher, independent of the investigated species. For cgMLST and SNP analysis results, we found that technological sequencing artefacts could be reduced by the use of filters, and that SNP analysis was more suited than cgMLST to compare data of different contributors. Regarding the four species, a minority of Campylobacter isolate data showed the in comparison highest divergence with regard to sequence type and cgMLST analysis. We additionally compared the assembler SPAdes and SKESA for their performance on the Illumina data sets of the different species and library preparation methods and found overall similar assembly quality metrics and cgMLST statistics.

Phylogeny and spatiotemporal dynamics of hepatitis E virus infections in wild boar and deer from six areas of Germany during 2013-2017.

The hepatitis E virus (HEV) can cause acute and chronic hepatitis in humans. Infections with the zoonotic HEV genotype 3, which can be transmitted from infected wild boar and deer to humans, are increasingly detected in Europe. To investigate the spatiotemporal HEV infection dynamics in wild animal populations, a study involving 3572 samples of wild boar and three deer species from six different geographic areas in Germany over a 4-year period was conducted. The HEV-specific antibody detection rates increased between 2013-2014 and 2016-2017 in wild boar from 9.5% to 22.8%, and decreased in deer from 1.1% to 0.2%. At the same time, HEV-RNA detection rates increased in wild boar from 2.8% to 13.3% and in deer from 0.7% to 4.2%. Marked differences were recorded between the investigated areas, with constantly high detection rates in one area and new HEV introductions followed by increasing detection rates in others. Molecular typing identified HEV subtypes 3c, 3f, 3i and a putative new subtype related to Italian wild boar strains. In areas, where sufficient numbers of positive samples were available for further analysis, a specific subtype dominated over the whole observation period. Phylogenetic analysis confirmed the close relationship between strains from the same area and identified closely related human strains from Germany. The results suggest that the HEV infection dynamics in wild animals is dependent on the particular geographical area where area-specific dominant strains circulate over a long period. The virus can spread from wild boar, which represent the main wild animal reservoir, to deer, and generally from wild animals to humans.

German-Wide Interlaboratory Study Compares Consistency, Accuracy and Reproducibility of Whole-Genome Short Read Sequencing.

We compared the consistency, accuracy and reproducibility of next-generation short read sequencing between ten laboratories involved in food safety (research institutes, state laboratories, universities and companies) from Germany and Austria. Participants were asked to sequence six DNA samples of three bacterial species (Campylobacter jejuni, Listeria monocytogenes and Salmonella enterica) in duplicate, according to their routine in-house sequencing protocol. Four different types of Illumina sequencing platforms (MiSeq, NextSeq, iSeq, NovaSeq) and one Ion Torrent sequencing instrument (S5) were involved in the study. Sequence quality parameters were determined for all data sets and centrally compared between laboratories. SNP and cgMLST calling were performed to assess the reproducibility of sequence data collected for individual samples. Overall, we found Illumina short read data to be more accurate (higher base calling accuracy, fewer miss-assemblies) and consistent (little variability between independent sequencing runs within a laboratory) than Ion Torrent sequence data, with little variation between the different Illumina instruments. Two laboratories with Illumina instruments submitted sequence data with lower quality, probably due to the use of a library preparation kit, which shows difficulty in sequencing low GC genome regions. Differences in data quality were more evident after assembling short reads into genome assemblies, with Ion Torrent assemblies featuring a great number of allele differences to Illumina assemblies. Clonality of samples was confirmed through SNP calling, which proved to be a more suitable method for an integrated data analysis of Illumina and Ion Torrent data sets in this study.

The Barcoding Table of Animal Species (BaTAnS): a new tool to select appropriate methods for animal species identification using DNA barcoding.

Food and feed products derived from animal materials have a long history of being adulterated. Methods for the identification of animal samples based on DNA barcoding are very potent tools to reveal species substitution. Since numerous DNA barcoding methods are available for different taxa, it is challenging to choose an appropriate and verified method for each sample in question. To overcome this obstacle the working group "Molecular biological methods for plant and animal species differentiation" developed the "Barcoding Table of Animal Species". This working group is established through the German food and feed law and is mandated to validate standard methods, especially for the official food and feed control laboratories in Germany. In this paper, a collection of currently available and verified DNA barcoding methods for the identification of animal species is presented as a Microsoft Excel® file-"The Barcoding Table of Animal Species (BaTAnS)". It consists of several components: The method collection, the results collection and a section for reporting new entries and problems. It is focusing on the validity and applicability of DNA barcoding methods to test food and feed products for correct species declaration. Each method is listed with its reference and is verified by at least two laboratories for their applicability. Since additional information will be available in future, this table will be updated regularly. The BaTAnS is an easy tool that helps to choose the right verified method to identify a certain specimen to taxon, genus or species level in food samples.

Hepatitis E Virus in Wild Boars and Spillover Infection in Red and Roe Deer, Germany, 2013-2015.

To determine animal hepatitis E virus (HEV) reservoirs, we analyzed serologic and molecular markers of HEV infection among wild animals in Germany. We detected HEV genotype 3 strains in inner organs and muscle tissues of a high percentage of wild boars and a lower percentage of deer, indicating a risk for foodborne infection of humans.

Comparison and optimization of detection methods for noroviruses in frozen strawberries containing different amounts of RT-PCR inhibitors.

Frozen berries have been repeatedly identified as vehicles for norovirus (NoV) transmission causing large gastroenteritis outbreaks. However, virus detection in berries is often hampered by the presence of RT-PCR-inhibiting substances. Here, several virus extraction methods for subsequent real-time RT-PCR-based NoV-RNA detection in strawberries were compared and optimized. NoV recovery rates (RRs) between 0.21 ± 0.13% and 10.29 ± 6.03% were found when five different artificially contaminated strawberry batches were analyzed by the ISO/TS15216-2 method indicating the presence of different amounts of RT-PCR inhibitors. A comparison of five different virus extraction methods using artificially contaminated strawberries containing high amounts of RT-PCR inhibitors revealed the best NoV RRs for the ISO/TS15216 method. Further improvement of NoV RRs from 2.83 ± 2.92% to 15.28 ± 9.73% was achieved by the additional use of Sephacryl(®)-based columns for RNA purification. Testing of 22 frozen strawberry samples from a batch involved in a gastroenteritis outbreak resulted in 5 vs. 13 NoV GI-positive and in 9 vs. 20 NoV GII-positive samples using the original ISO/TS15216 method vs. the extended protocol, respectively. It can be concluded that the inclusion of an additional RNA purification step can increase NoV detection by the ISO/TS15216-2 method in frozen berries containing high amounts of RT-PCR inhibitors.

Detection of hepatitis E virus RNA in raw sausages and liver sausages from retail in Germany using an optimized method.

Hepatitis E virus (HEV) is a pathogen of increasing importance, which can be zoonotically transmitted from domestic pigs, wild boar, and deer to humans. Foodborne transmission by consumption of raw and undercooked liver, meat, or sausages prepared from infected animals has been documented. The aim of this study was to investigate the distribution of HEV in different types of sausages sold in Germany. As no standardized methods for HEV detection in food exist, several techniques of sample homogenization, virus concentration and nucleic acid extraction followed by real-time RT-PCR were compared using artificially contaminated sausages. A method using TRI Reagent® Solution showed the best efficacy of matrix disruption and a treatment with chloroform followed by a silica-based RNA extraction method resulted in the highest HEV detection rates. The detection limit of the method was 2.9 × 10(3) and 5.3 × 10(4) genome equivalents per 5 g raw sausage and 2 g liver sausage, respectively. Application of the method to raw and liver sausages from retail in Germany resulted in the HEV genome detection in 14 out of 70 (20%) raw sausages and in 11 out of 50 (22%) liver sausages. The detected HEV sequences showed a high diversity and belonged to different subtypes of HEV genotype 3. The results indicate a broad distribution of HEV-RNA in meat products sold in Germany; however, the infectivity of the detected virus remains to be assessed in future.