Biology subjects

Dallman, T.

Publications and source records attributed to Dallman, T..

6 recordsLinked to original sources

bioRxiv2026

Population analysis and host-disease associations of Shiga toxin-producing Escherichia coli from various sources across eleven European countries using whole genome sequencing

Shiga toxin-producing Escherichia coli (STEC) are important foodborne pathogens, able to cause severe disease in humans. In the DiSCoVeR project (https://onehealthejp.eu/jrp-discover/) a STEC inventory from human and non-human sources from 11 European countries was set up and [≥] 3500 strains were sequenced to perform comparative genomics analysis. We used this dataset to assess STEC population structure and to investigate potential associations between genomic features, host reservoirs and symptoms. Most STEC isolates analysed by Whole Genome Sequencing (WGS) in this study were collected between years 2010-2020. An ad hoc pipeline was deployed for a harmonised characterization of the STEC in the database, allowing the determination of serotyping, stx gene subtyping, 7-loci MLST, virulotyping and cgMLST. The results were analysed with Principal Component Analysis (PCoA) in relation with isolation source to assess clustering of STEC subpopulations. When human STEC data were analysed, the PCoA revealed three distinct human STEC subpopulations (STEC_1, STEC_2 and STEC_3), which were further analysed for associations between genomic features, symptoms and variance. The non-human STEC showed a more dispersed distribution, except for one subpopulation with genes linked to specific host species, and some virulence profiles overlapping with the STEC_1 population. In conclusion, our analysis identified distinct STEC subpopulations from human cases, each characterized by specific genetic features and associated with varying proportions of severe disease outcomes. These findings provide novel insights supporting the risk assessment of STEC. Impact statement[This lay summary of your article should be no more than 200 words, and should a) provide a perspective of how this article adds to the literature in the field; b) identify breadth of interest/utility; and c) state the significance of output (incremental or step), in terms of relevance.] This study is based on the establishment of a One Health STEC genomes database, including sequences from isolates of different sources. Most of the isolates had been isolated in the ten-years time span 2010-2020, in 11 different countries, for surveillance and monitoring activities or specific surveys and research purposes. The final dataset included the whole genome sequencing of 3,418 STEC isolates, mainly from human cases of infections. The metadata included the host symptoms, where available, for human STEC strains and the animal source the strains had been isolated from. We set up a pipeline for the harmonized analysis of STEC WGS, called Discover, made available though ARIES webserver or GitHub. The analysis allowed a deep characterization of STEC strains circulating in Europe. We used this resource to assess STEC population structure and to investigate potential associations between genomic features, host reservoirs, and various symptoms associated with STEC infection by PCoA. This analysis highlighted the presence of subpopulation of human STEC associated with specific features. We provide new information useful for risk characterization, as well as a large dataset genome database and associated metadata compiled from STEC strains, representing a valuable resource for the scientific community, enabling further investigations into STEC diversity, evolution, source attribution and public health relevance. Data summaryThe authors confirm all supporting data, including sequence data accession numbers, code and protocols have been provided within the article or through supplementary data files. One supplementary method and five supplementary tables are available with the online version of this article

genomics↗

bioRxiv2025

Phage-encoded sRNA counteracts xenogenic silencing in pathogenic E. coli

Horizontal gene transfer introduces foreign DNA that can disrupt cellular processes and is therefore subject to xenogenic silencing by nucleoid-associated proteins such as H-NS and Hha. In Enterohaemorrhagic Escherichia coli (EHEC), prophages make up a large fraction of the accessory genome and encode many virulence factors, yet to be expressed they must overcome this silencing. We identify a prophage-encoded small RNA (sRNA), HnrS, that functions as an anti-silencing factor by targeting the H-NS paralogue Hha. HnrS is a short (66-nt) sRNA present in multiple copies (up to nine) in EHEC and Enteropathogenic Escherichia coli (EPEC) genomes and is enriched in E. coli strains that carry the locus of enterocyte effacement (LEE). We show that HnrS directly base-pairs with the ribosome-binding site of the hha mRNA, repressing its translation and thereby reducing Hha-enhanced H-NS silencing. This counter-silencing de-represses the LEE type III secretion system and concomitantly represses motility. Transcriptomic profiling further revealed that HnrS indirectly activates genes involved in nitrate/nitrite respiration and nitric oxide resistance, metabolic pathways that contribute to survival in the inflamed gastrointestinal tract. Deletion of hnrS reduced expression of nitrate reductase genes and impaired actin pedestal formation on host epithelial cells. Our results indicate that prophage-encoded, multicopy hnrS provides a counter-silencing mechanism that reduces Hha-H-NS repression at specific virulence loci. This likely enables expression of horizontally acquired genes without broadly disrupting the core H-NS regulon. HnrS illustrates how mobile genetic elements deploy sRNAs to counteract xenogenic silencing and promote virulence gene expression, enhancing colonisation of the host. Importance statementHorizontally acquired genes are often silenced to protect bacterial genomes, but this defence also limits the expression of new traits. We identify a prophage-encoded small RNA, HnrS, that counteracts this restriction by repressing the xenogenic silencer Hha, lifting Hha-H-NS-mediated repression of virulence and metabolic genes. HnrS activates the locus of enterocyte effacement, nitrate/nitrite respiration, and nitric oxide resistance--pathways that help E. coli survive and colonise the inflamed gut. Our findings reveal an RNA-based counter-silencing mechanism encoded by mobile genetic elements, showing how phages can reprogram bacterial regulatory networks to promote adaptation and pathogenicity.

microbiology↗

bioRxiv2023

Salmonella Infantis, the emerging human multidrug resistant pathogen - a One Health perspective

Salmonella Infantis presents an ever-increasing threat to public health due to its spread throughout many countries and association with high levels of antimicrobial resistance (AMR). Whole genome sequences of 5,284 S. Infantis strains from 74 countries, isolated between 1989 and 2020 from a wide variety of sources including humans, animals, and food, were analysed to compare genetic phylogeny, AMR determinants and plasmid presence. The global S. Infantis population structure diverged into three clusters: a North American cluster, European cluster and a global cluster. The levels of AMR varied between the S. Infantis clusters and by isolation source; 73% of poultry isolates had multidrug resistance (MDR) compared to 35% of human isolates. This correlated with plasmid of emerging S. Infantis (pESI) presence; 71% of poultry isolates contained pESI versus 32% of human isolates. This provides important information for public health teams engaged in reducing the spread of this pathogen.

microbiology↗

bioRxiv2019

Comparison of Shiga toxin-encoding bacteriophages in highly pathogenic strains of Shiga toxin-producing Escherichia coli O157:H7 in the UK.

2.Over the last 35 years in the UK the burden of Shiga toxin-producing Escherichia coli (STEC) O157:H7 infection has, during different periods of time, been associated with five different sub-lineages (1983-1995: Ia, I/IIa and I/IIb, 1996-2014: Ic and 2015-2018: IIb). The acquisition of a stx2a-encoding bacteriophage by these five sub-lineages appears to have coincided with their respective emergences. Oxford Nanopore Technology (ONT) was used to sequence, characterise and compare the stx-encoding prophage harboured by each sub-lineage to investigate the integration of this key virulence factor. The stx2a-encoding prophage from each of the lineages causing clinical disease in the UK were all different, including the two UK sub-lineages (Ia and I/IIa) circulating concurrently and causing severe disease in the early 1980s. Comparisons between the stx2a-encoding prophage in sub-lineages I/IIb and IIb revealed similarity to the prophage commonly found to encode stx2c, and the same site of bacteriophage integration (sbcB) as stx2c encoding prophage. These data suggest independent acquisition of previously unobserved stx2a-encoding phage is more likely to have contributed to the emergence of STEC O157:H7 sub-lineages in the UK than intra-UK lineage to lineage phage transmission. In contrast, the stx2c-encoding prophage showed a high level of similarity across lineage and time, consistent with the model of stx2c being present in the common ancestor to extant STEC O157:H7 and maintained by vertical inheritance in the majority of the population. Studying the nature of the stx-encoding bacteriophage contributes to our understanding of the emergence of highly pathogenic strains of STEC O157:H7. 3. Impact statementThe application of ONT technology to sequence UK epidemic strains of STEC O157:H7 revealed stx2a-encoding prophage exhibit a high level of diversity. There was little evidence of geographical or temporal patterns of relatedness, or of intra-UK transmission of stx2a-encoding prophage between indigenous strains. The stx2a-encoding prophage in the UK lineages associated with severe disease appear to be acquired independently and most likely from different geographical and/or environmental sources. These data provide supporting evidence for the existence of a dynamic environmental reservoir of stx2a-encoding prophage that pose a threat public health due to their potential for integration into competent, indigenous sub-lineages of STEC O157:H7. We also provide further evidence that stx2c-encoding prophage exhibit a high level of similarity across lineage, geographical region and time, and have likely been maintained and inherited vertically. 4. Data summaryAll FASTQ files and assemblies of samples sequenced in this project were submitted to the National Centre for Biotechnology Information (NCBI). All data can be found under BioProject: PRJNA315192 - https://www.ncbi.nlm.nih.gov/bioproject/?term=PRJNA315192. Strain specific details can be found in the methods section under data deposition. Publicly available data used in this project can be found via Table 1 and data bibliography. O_TBL View this table: org.highwire.dtl.DTLVardef@178103aorg.highwire.dtl.DTLVardef@1718d1corg.highwire.dtl.DTLVardef@1e7605forg.highwire.dtl.DTLVardef@1683451org.highwire.dtl.DTLVardef@42c400_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1 -C_FLOATNO O_TABLECAPTIONSummary of the PHE archived and publicly available strains used within this study, their Strain ID, lineage, phage type, Stx profile, assembly accession numbers and NCBI BioProject. C_TABLECAPTION C_TBL

genomics↗

bioRxiv2019

Comparison of single nucleotide variants identified by Illumina and Oxford Nanopore technologies in the context of a potential outbreak of Shiga Toxin Producing Escherichia coli.

BackgroundWe aimed to compare Illumina and Oxford Nanopore Technology (ONT) sequencing data from the two isolates of STEC O157:H7 to determine whether concordant single nucleotide variants were identified and whether inference of relatedness was consistent with the two technologies.\n\nResultsFor the Illumina workflow, the time from DNA extraction to availability of results, was approximately 40 hours in comparison to the ONT workflow where serotyping, Shiga toxin subtyping variant identification were available within seven hours. After optimisation of the ONT variant filtering, on average 95% of the discrepant positions between the technologies were accounted for by methylated positions found in the described 5-Methylcytosine motif sequences, CC(A/T)GG. Of the few discrepant variants (6 and 7 difference for the two isolates) identified by the two technologies, it is likely that both methodologies contain false calls.\n\nConclusionsDespite these discrepancies, Illumina and ONT sequences from the same case were placed on the same phylogenetic location against a dense reference database of STEC O157:H7 genomes sequenced using the Illumina workflow. Robust SNP typing using MinION-based variant calling is possible and we provide evidence that the two technologies can be used interchangeably to type STEC O157:H7 in a public health setting.

microbiology↗

bioRxiv2017

Salmonella enterica Serovar Typhimurium ST313 Responsible For Gastroenteritis In The UK Are Genetically Distinct From Isolates Causing Bloodstream Infections In Africa

The ST313 sequence type of Salmonella enterica serovar Typhimurium causes invasive non-typhoidal salmonellosis amongst immunocompromised people in sub-Saharan Africa (sSA). Previously, two distinct phylogenetic lineages of ST313 have been described which have rarely been found outside sSA. Following the introduction of routine whole genome sequencing of Salmonella enterica by Public Health England in 2014, we have discovered that 2.7% (79/2888) of S. Typhimurium from patients in England and Wales are ST313. Of these isolates, 59/72 originated from stool and 13/72 were from extra-intestinal sites. The isolation of ST313 from extra-intestinal sites was significantly associated with travel to Africa (OR 12 [95% CI: 3,53]). Phylogenetic analysis revealed previously unsampled diversity of ST313, and distinguished UK-linked isolates causing gastroenteritis from African-associated isolates causing invasive disease. Bayesian evolutionary investigation suggested that the two African lineages diverged from their most recent common ancestors independently, circa 1796 and 1903. The majority of genome degradation of African ST313 lineage 2 is conserved in the UK ST313 lineages and only 10/44 pseudogenes were lineage 2-specific. The African lineages carried a characteristic prophage and antibiotic resistance gene repertoire, suggesting a strong selection pressure for these horizontally-acquired genetic elements in the sSA setting. We identified an ST313 isolate associated with travel to Kenya that carried a chromosomally-located blaCTX-M-15, demonstrating the continual evolution of this sequence type in Africa in response to selection pressure exerted by antibiotic usage.\n\nThe S. Typhimurium ST313 sequence type has been primarily associated with invasive disease in Africa. Here, we highlight the power of routine whole-genome-sequencing by public health agencies to make epidemiologically-significant deductions that would be missed by conventional microbiological methods. The discovery of ST313 isolates responsible for gastroenteritis in the UK reveals new diversity in this important sequence type. We speculate that the niche specialization of sub-Saharan African ST313 lineages is driven in part by the acquisition of accessory genome elements.

microbiology↗