Imperial College London

DrXavierDidelot

Faculty of MedicineSchool of Public Health

Visiting Professor
 
 
 
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Contact

 

+44 (0)20 7594 3622x.didelot

 
 
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Location

 

G30Medical SchoolSt Mary's Campus

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Summary

 

Publications

Publication Type
Year
to

154 results found

Didelot X, Geidelberg L, COVID-19 Genomics UK COG-UK consortium, Volz EMet al., 2021, Model design for non-parametric phylodynamic inference and applications to pathogen surveillance., bioRxiv

Inference of effective population size from genomic data can provide unique information about demographic history, and when applied to pathogen genetic data can also provide insights into epidemiological dynamics. The combination of non-parametric models for population dynamics with molecular clock models which relate genetic data to time has enabled phylodynamic inference based on large sets of time-stamped genetic sequence data. The methodology for non-parametric inference of effective population size is well-developed in the Bayesian setting, but here we develop a frequentist approach based on non-parametric latent process models of population size dynamics. We appeal to statistical principles based on out-of-sample prediction accuracy in order to optimize parameters that control shape and smoothness of the population size over time. We demonstrate the flexibility and speed of this approach in a series of simulation experiments, and apply the methodology to reconstruct the previously described waves in the seventh pandemic of cholera. We also estimate the impact of non-pharmaceutical interventions for COVID-19 in England using thousands of SARS-CoV-2 sequences. By incorporating a measure of the strength of these interventions over time within the phylodynamic model, we estimate the impact of the first national lockdown in the UK on the epidemic reproduction number.

Journal article

Helekal D, Ledda A, Volz E, Wyllie D, Didelot Xet al., 2021, Bayesian inference of clonal expansions in a dated phylogeny

<jats:p>Microbial population genetics models often assume that all lineages are constrained by the same population size dynamics over time. However, many neutral and selective events can invalidate this assumption, and can contribute to the clonal expansion of a specific lineage relative to the rest of the population. Such differential phylodynamic properties between lineages result in asymmetries and imbalances in phylogenetic trees that are sometimes described informally but difficult to analyse formally. To this end, we developed a model of how clonal expansions occur and affect the branching patterns of a phylogeny. We show how the parameters of this model can be inferred from a given dated phylogeny using Bayesian statistics, which allows us to assess the probability that one or more clonal expansion events occurred. For each putative clonal expansion event we estimate their date of emergence and subsequent phylodynamic trajectories, including their long-term evolutionary potential which is important to determine how much effort should be placed on specific control measures. We demonstrate the usefulness of our methodology on simulated and real datasets.</jats:p>

Journal article

Knight DR, Imwattana K, Kullin B, Guerrero-Araya E, Paredes-Sabja D, Didelot X, Dingle KE, Eyre DW, Rodriguez C, Riley Tet al., 2021, Major genetic discontinuity and novel toxigenic species in Clostridioides difficile taxonomy, ELIFE, Vol: 10, ISSN: 2050-084X

Journal article

Didelot X, Kendall M, Xu Y, White PJ, McCarthy Net al., 2021, Genomic epidemiology analysis of infectious disease outbreaks using TransPhylo., Current Protocols, Vol: 1, Pages: 1-23, ISSN: 2691-1299

Comparing the pathogen genomes from several cases of an infectious disease has the potential to help us understand and control outbreaks. Many methods exist to reconstruct a phylogeny from such genomes, which represents how the genomes are related to one another. However, such a phylogeny is not directly informative about transmission events between individuals. TransPhylo is a software tool implemented as an R package designed to bridge the gap between pathogen phylogenies and transmission trees. TransPhylo is based on a combined model of transmission between hosts and pathogen evolution within each host. It can simulate both phylogenies and transmission trees jointly under this combined model. TransPhylo can also reconstruct a transmission tree based on a dated phylogeny, by exploring the space of transmission trees compatible with the phylogeny. A transmission tree can be represented as a coloring of a phylogeny where each color represents a different host of the pathogen, and TransPhylo provides convenient ways to plot these colorings and explore the results. This article presents the basic protocols that can be used to make the most of TransPhylo. © 2021 The Authors. Basic Protocol 1: First steps with TransPhylo Basic Protocol 2: Simulation of outbreak data Basic Protocol 3: Inference of transmission Basic Protocol 4: Exploring the results of inference.

Journal article

Lassalle F, Dastgheib SMM, Zhao F-J, Zhang J, Verbag S, Fruhling A, Brinkmann H, Osborne T, Sikorski J, Balloux F, Didelot X, Santini J, Petersen Jet al., 2021, Phylogenomics reveals the basis of adaptation of Pseudorhizobium species to extreme environments and supports a taxonomic revision of the genus, Systematic and Applied Microbiology, Vol: 44, Pages: 1-14, ISSN: 0172-5564

The family Rhizobiaceae includes many genera of soil bacteria, often isolated for their association with plants. Herein, we investigate the genomic diversity of a group of Rhizobium species and unclassified strains isolated from atypical environments, including seawater, rock matrix or polluted soil. Based on whole-genome similarity and core genome phylogeny, we show that this group corresponds to the genus Pseudorhizobium. We thus reclassify Rhizobium halotolerans, R. marinum, R. flavum and R. endolithicum as P. halotolerans sp. nov., P. marinum comb. nov. , P. flavum comb. nov. and P. endolithicum comb. nov. , respectively, and show that P. pelagicum is a synonym of P. marinum . We also delineate a new chemolithoautotroph species, P. banfieldiae sp. nov. , whose type strain is NT-26 T (= DSM 106348 T = CFBP 8663 T ) . This genome-based classification was supported by a chemotaxonomic comparison, with increasing taxonomic resolution provided by fatty acid, protein and metabolic profiles. In addition, we used a phylogenetic approach to infer scenarios of duplication, horizontal transfer and loss for all genes in the Pseudorhizobium pangenome. We thus identify the key functions associated with the diversification of each species and higher clades, shedding light on the mechanisms of adaptation to their respective ecological niches. Respiratory proteins acquired at the origin of Pseudorhizobium were combined with clade-specific genes to enable different strategies for detoxification and nutrition in harsh, nutrient- poor environments.

Journal article

Didelot X, Siveroni I, Volz EM, 2021, Additive uncorrelated relaxed clock models for the dating of genomic epidemiology phylogenies, Molecular Biology and Evolution, Vol: 38, Pages: 307-317, ISSN: 0737-4038

Phylogenetic dating is one of the most powerful and commonly used methods of drawing epidemiological interpretations from pathogen genomic data. Building such trees requires considering a molecular clock model which represents the rate at which substitutions accumulate on genomes. When the molecular clock rate is constant throughout the tree then the clock is said to be strict, but this is often not an acceptable assumption. Alternatively, relaxed clock models consider variations in the clock rate, often based on a distribution of rates for each branch. However, we show here that the distributions of rates across branches in commonly used relaxed clock models are incompatible with the biological expectation that the sum of the numbers of substitutions on two neighbouring branches should be distributed as the substitution number on a single branch of equivalent length. We call this expectation the additivity property. We further show how assumptions of commonly used relaxed clock models can lead to estimates of evolutionary rates and dates with low precision and biased confidence intervals. We therefore propose a new additive relaxed clock model where the additivity property is satisfied. We illustrate the use of our new additive relaxed clock model on a range of simulated and real datasets, and we show that using this new model leads to more accurate estimates of mean evolutionary rates and ancestral dates.

Journal article

Hennart M, Panunzi LG, Rodrigues C, Gaday Q, Baines SL, Barros-Pinkelnig M, Carmi-Leroy A, Dazas M, Wehenkel AM, Didelot X, Toubiana J, Badell E, Brisse Set al., 2020, Population genomics and antimicrobial resistance in Corynebacterium diphtheriae, GENOME MEDICINE, Vol: 12, ISSN: 1756-994X

Journal article

Fountain-Jones NM, Appaw RC, Carver S, Didelot X, Volz E, Charleston Met al., 2020, Emerging phylogenetic structure of the SARS-CoV-2 pandemic., Virus Evol, Vol: 6, ISSN: 2057-1577

Since spilling over into humans, SARS-CoV-2 has rapidly spread across the globe, accumulating significant genetic diversity. The structure of this genetic diversity and whether it reveals epidemiological insights are fundamental questions for understanding the evolutionary trajectory of this virus. Here, we use a recently developed phylodynamic approach to uncover phylogenetic structures underlying the SARS-CoV-2 pandemic. We find support for three SARS-CoV-2 lineages co-circulating, each with significantly different demographic dynamics concordant with known epidemiological factors. For example, Lineage C emerged in Europe with a high growth rate in late February, just prior to the exponential increase in cases in several European countries. Non-synonymous mutations that characterize Lineage C occur in functionally important gene regions responsible for viral replication and cell entry. Even though Lineages A and B had distinct demographic patterns, they were much more difficult to distinguish. Continuous application of phylogenetic approaches to track the evolutionary epidemiology of SARS-CoV-2 lineages will be increasingly important to validate the efficacy of control efforts and monitor significant evolutionary events in the future.

Journal article

Osnes MN, Didelot X, de Korne-Elenbaas J, Alfsnes K, Brynildsrud OB, Syversen G, Nilsen OJ, De Blasio BF, Caugant DA, Eldholm Vet al., 2020, Sudden emergence of a Neisseria gonorrhoeae Glade with reduced susceptibility to extended-spectrum cephalosporins, Norway, MICROBIAL GENOMICS, Vol: 6, ISSN: 2057-5858

Journal article

Zhao L, Chen H, Didelot X, Li Z, Li Y, Chen M, Du Y, Zhao H, Li J, Hu Q, Kan B, Chen M, Pang Bet al., 2020, Co-existence of multiple distinct lineages in Vibrio parahaemolyticus serotype O4:K12, MICROBIAL GENOMICS, Vol: 6, ISSN: 2057-5858

Journal article

Celma CC, Beard S, Douglas A, Wong S, Osafo N-K, Hannah M, Hale A, Huggins G, Ladhani S, Dunning Jet al., 2020, Retrospective analysis on confirmation rates for referred positive rotavirus samples in England, 2016 to 2017: implications for diagnosis and surveillance, Eurosurveillance, Vol: 25, Pages: 1-8, ISSN: 1025-496X

BackgroundRapid diagnostic tests are commonly used by hospital laboratories in England to detect rotavirus (RV), and results are used to inform clinical management and support national surveillance of the infant rotavirus immunisation programme since 2013. In 2017, the Public Health England (PHE) national reference laboratory for enteric viruses observed that the presence of RV could not be confirmed by PCR in a proportion of RV-positive samples referred for confirmatory detection.AimWe aimed to compare the positivity rate of detection methods used by hospital laboratories with the PHE confirmatory test rate.MethodsRotavirus specimens testing positive at local hospital laboratories were re-tested at the PHE national reference laboratory using a PCR test. Confirmatory results were compared to original results from the PHE laboratory information management system.ResultsHospital laboratories screened 70.1% (2,608/3,721) of RV samples using immunochromatographic assay (IC) or rapid tests, 15.5% (578/3,721) using enzyme immunoassays (EIA) and 14.4% (535/3,721) using PCR. Overall, 1,011/3,721 (27.2%) locally RV-positive samples referred to PHE in 2016 and 2017 failed RV detection using the PHE reference laboratory PCR test. Confirmation rates were 66.9% (1,746/2,608) for the IC tests, 87.4% (505/578) for the EIA and 86.4% (465/535) for the PCR assays. Seasonal confirmation rate discrepancies were also evident for IC tests.ConclusionsThis report highlights high false positive rates with the most commonly used RV screening tests and emphasises the importance of implementing verified confirmatory tests for RV detections. This has implications for clinical diagnosis and national surveillance.

Journal article

Whittles LK, White PJ, Didelot X, 2020, Assessment of the potential of vaccination to combat antibiotic resistance in gonorrhea: a modeling analysis to determine preferred product characteristics, Clinical Infectious Diseases, Vol: 71, Pages: 1912-1919, ISSN: 1058-4838

BACKGROUND: Gonorrhea incidence is increasing rapidly in many countries, whilst antibiotic resistance is making treatment more difficult. Combined with evidence that MeNZB and Bexsero meningococcal vaccines are likely partially-protective against gonorrhea, this has renewed interest in a gonococcal vaccine, and several candidates are in development. Key questions are how protective a vaccine needs to be, how long protection needs to last, and how should it be targeted. We assessed vaccination's potential impact, and the feasibility of achieving WHO's target 90% reduction in gonorrhea incidence 2016-2030, by comparing realistic vaccination strategies under a range of scenarios of vaccine efficacy and duration of protection, and emergence of extensively-resistant gonorrhea. METHODS: We developed a stochastic transmission-dynamic model, incorporating asymptomatic and symptomatic infection and heterogeneous sexual behavior in men-who-have-sex-with-men (MSM). We used data from England, which has a comprehensive, consistent nationwide surveillance system. Using particle Markov Chain Monte Carlo methods we fitted the model to gonorrhea incidence in 2008-17, and then used Bayesian forecasting to examine an extensive range of scenarios. RESULTS: Even in the worst-case scenario of untreatable infection emerging, the WHO target is achievable if all MSM attending sexual health clinics receive a vaccine offering ≥52% protection for ≥6 years. A vaccine conferring 31% protection (as estimated for MeNZB) for 2-4 years, could reduce incidence in 2030 by 45% in the worst-case scenario, and by 75% if >70% of resistant gonorrhea remains treatable. CONCLUSIONS: Even a partially-protective vaccine, delivered through a realistic targeting strategy, could substantially reduce gonorrhea incidence, despite antibiotic resistance.

Journal article

Wang L, Didelot X, Yang J, Wong G, Shi Y, Liu W, Gao GF, Bi Yet al., 2020, Inference of person-to-person transmission of COVID-19 reveals hidden super-spreading events during the early outbreak phase, NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723

Journal article

Janezic S, Dingle K, Alvin J, Accetto T, Didelot X, Crook DW, Lacy DB, Rupnik Met al., 2020, Comparative genomics of Clostridioides difficile toxinotypes identifies module-based toxin gene evolution, MICROBIAL GENOMICS, Vol: 6, ISSN: 2057-5858

Journal article

Volz E, Wiuf C, Grad YH, Frost SDW, Dennis AM, Didelot Xet al., 2020, Identification of hidden population structure in time-scaled phylogenies, Systematic Biology, Vol: 69, Pages: 884-896, ISSN: 1063-5157

Abstract Population structure influences genealogical patterns, however data pertaining to how populations are structured are often unavailable or not directly observable. Inference of population structure is highly important in molecular epidemiology where pathogen phylogenetics is increasingly used to infer transmission patterns and detect outbreaks. Discrepancies between observed and idealised genealogies, such as those generated by the coalescent process, can be quantified, and where significant differences occur, may reveal the action of natural selection, host population structure, or other demographic and epidemiological heterogeneities. We have developed a fast non-parametric statistical test for detection of cryptic population structure in time-scaled phylogenetic trees. The test is based on contrasting estimated phylogenies with the theoretically expected phylodynamic ordering of common ancestors in two clades within a coalescent framework. These statistical tests have also motivated the development of algorithms which can be used to quickly screen a phylogenetic tree for clades which are likely to share a distinct demographic or epidemiological history. Epidemiological applications include identification of outbreaks in vulnerable host populations or rapid expansion of genotypes with a fitness advantage. To demonstrate the utility of these methods for outbreak detection, we applied the new methods to large phylogenies reconstructed from thousands of HIV-1 partial pol sequences. This revealed the presence of clades which had grown rapidly in the recent past, and was significantly concentrated in young men, suggesting recent and rapid transmission in that group. Furthermore, to demonstrate the utility of these methods for the study of antimicrobial resistance, we applied the new methods to a large phylogeny reconstructed from whole genome Neisseria gonorrhoeae sequences. We find that population structure detected using these methods closely overlaps with th

Journal article

Lassalle F, Didelot X, 2020, Bacterial microevolution and the pangenome, The Pangenome: Diversity, Dynamics and Evolution of Genomes, Pages: 129-149, ISBN: 9783030382803

The comparison of multiple genome sequences sampled from a bacterial population reveals considerable diversity in both the core and the accessory parts of the pangenome. This diversity can be analysed in terms of microevolutionary events that took place since the genomes shared a common ancestor, especially deletion, duplication, and recombination. We review the basic modelling ingredients used implicitly or explicitly when performing such a pangenome analysis. In particular, we describe a basic neutral phylogenetic framework of bacterial pangenome microevolution, which is not incompatible with evaluating the role of natural selection. We survey the different ways in which pangenome data is summarised in order to be included in microevolutionary models, as well as the main methodological approaches that have been proposed to reconstruct pangenome microevolutionary history.

Book chapter

Ledda A, Cummins M, Shaw LP, Jauneikaite E, Cole K, Lasalle F, Barry D, Rosmarin C, Anaraki S, Wareham D, Stoesser N, Paul J, Manuel R, Cherian BP, Didelot Xet al., 2020, Hospital outbreak of carbapenem-resistant Enterobacteriales associated with an OXA-48 plasmid carried mostly byEscherichia coliST399

<jats:title>Abstract</jats:title><jats:p>A hospital outbreak of carbapenem-resistant Enterobacteriales was detected by routine surveillance. Whole genome sequencing and subsequent analysis revealed a conserved promiscuous OXA-48 carrying plasmid as the defining factor within this outbreak. Four different species of Enterobacteriales were involved in the outbreak.<jats:italic>Escherichia coli</jats:italic>ST399 accounted for 20/55 of all the isolates. Comparative genomics with publicly available<jats:italic>E. coli</jats:italic>ST399 sequence data showed that the outbreak isolates formed a unique clade. The OXA-48 plasmid identified in the outbreak differed from other known plasmids by an estimated five homologous recombination events. We estimated a lower bound to the plasmid conjugation rate to be 0.23 conjugation events per lineage per year. Our analysis suggests co-evolution between the plasmid and its main bacterial host to be a key driver of the outbreak. This is the first study to report carbapenem-resistant<jats:italic>E. coli</jats:italic>ST399 carrying OXA48 as the main cause of a plasmid-borne outbreak within a hospital setting. This study supports complementary roles for both plasmid conjugation and clonal expansion in the emergence of this outbreak.</jats:p>

Journal article

Rodriguez Manzano J, Moser N, Malpartida Cardenas K, Moniri A, Fisarova L, Pennisi I, Boonyasiri A, Jauneikaite E, Abdolrasouli A, Otter J, Bolt F, Davies F, Didelot X, Holmes A, Georgiou Pet al., 2020, Rapid detection of mobilized colistin resistance using a nucleic acid based lab-on-a-chip diagnostic system, Scientific Reports, Vol: 10, ISSN: 2045-2322

The increasing prevalence of antimicrobial resistance is a serious threat to global public health. One of the most concerning trends is the rapid spread of Carbapenemase-Producing Organisms (CPO), where colistin has become the last-resort antibiotic treatment. The emergence of colistin resistance, including the spread of mobilized colistin resistance (mcr) genes, raises the possibility of untreatable bacterial infections and motivates the development of improved diagnostics for the detection of colistin-resistant organisms. This work demonstrates a rapid response for detecting the most recently reported mcr gene, mcr−9, using a portable and affordable lab-on-a-chip (LoC) platform, offering a promising alternative to conventional laboratory-based instruments such as real-time PCR (qPCR). The platform combines semiconductor technology, for non-optical real-time DNA sensing, with a smartphone application for data acquisition, visualization and cloud connectivity. This technology is enabled by using loop-mediated isothermal amplification (LAMP) as the chemistry for targeted DNA detection, by virtue of its high sensitivity, specificity, yield, and manageable temperature requirements. Here, we have developed the first LAMP assay for mcr−9 - showing high sensitivity (down to 100 genomic copies/reaction) and high specificity (no cross-reactivity with other mcr variants). This assay is demonstrated through supporting a hospital investigation where we analyzed nucleic acids extracted from 128 carbapenemase-producing bacteria isolated from clinical and screening samples and found that 41 carried mcr−9 (validated using whole genome sequencing). Average positive detection times were 6.58 ± 0.42 min when performing the experiments on a conventional qPCR instrument (n = 41). For validating the translation of the LAMP assay onto a LoC platform, a subset of the samples were tested (n = 20), showing average detection times o

Journal article

Wang H, Yang C, Sun Z, Zheng W, Zhang W, Yu H, Wu Y, Didelot X, Yang R, Pan J, Cui Yet al., 2020, Genomic epidemiology of Vibrio cholerae reveals the regional and global spread of two epidemic non-toxigenic lineages, PLOS NEGLECTED TROPICAL DISEASES, Vol: 14, ISSN: 1935-2735

Journal article

Wang H, Yang C, Sun Z, Zheng W, Zhang W, Yu H, Wu Y, Didelot X, Yang R, Pan J, Cui Yet al., 2020, Genomic epidemiology of Vibrio cholerae reveals the regional and global spread of two epidemic non-toxigenic lineages., PLoS Negl Trop Dis, Vol: 14

Non-toxigenic Vibrio cholerae isolates have been found associated with diarrheal disease globally, however, the global picture of non-toxigenic infections is largely unknown. Among non-toxigenic V. cholerae, ctxAB negative, tcpA positive (CNTP) isolates have the highest risk of disease. From 2001 to 2012, 71 infectious diarrhea cases were reported in Hangzhou, China, caused by CNTP serogroup O1 isolates. We sequenced 119 V. cholerae genomes isolated from patients, carriers and the environment in Hangzhou between 2001 and 2012, and compared them with 850 publicly available global isolates. We found that CNTP isolates from Hangzhou belonged to two distinctive lineages, named L3b and L9. Both lineages caused disease over a long time period with usually mild or moderate clinical symptoms. Within Hangzhou, the spread route of the L3b lineage was apparently from rural to urban areas, with aquatic food products being the most likely medium. Both lineages had been previously reported as causing local endemic disease in Latin America, but here we show that global spread of them has occurred, with the most likely origin of L3b lineage being in Central Asia. The L3b lineage has spread to China on at least three occasions. Other spread events, including from China to Thailand and to Latin America were also observed. We fill the missing links in the global spread of the two non-toxigenic serogroup O1 V. cholerae lineages that can cause human infection. The results are important for the design of future disease control strategies: surveillance of V. cholerae should not be limited to ctxAB positive strains.

Journal article

Lassalle F, Veber P, Jauneikaite E, Didelot Xet al., 2019, Automated reconstruction of all gene histories in large bacterial pangenome datasets and search for co-evolved gene modules with Pantagruel

<jats:title>Abstract</jats:title><jats:p>The availability of bacterial pangenome data grows exponentially, requiring efficient new methods of analysis. Currently popular approaches for the fast comparison of genomes have the drawback of not being based on explicit evolutionary models of diversification. Making sense of bacterial genome evolution, and notably in the accessory genome, requires however to take into account the complex processes by which the genomes evolve. Here we present the <jats:italic>Pantagruel</jats:italic> bioinformatic software pipeline, which enables the construction of a complete bacterial pangenome database geared towards the inference of gene evolution scenarios using gene tree/species tree reconciliation. <jats:italic>Pantagruel</jats:italic> is a modular pipeline that combines state-of-the-art external software with unique new methods. It can be executed with no supervision to perform a standard pangenome analysis, or be configured by advanced users to integrate methods of choice. A relational database underlies its data structure, allowing efficient retrieval of the large-scale data generated by integrative analyses of pangenome evolutionary history. From the reconstructed gene evolution scenarios, two main outputs are derived: firstly the gene tree-aware assignation of orthology, allowing the fine analysis of gene gain and loss history over the species phylogeny, and secondly a network of gene-to-gene association based on correlated events in scenarios of gene evolution, leading to the definition of co-evolved gene modules. <jats:italic>Pantagruel</jats:italic> is available as an open source software package at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="https://github.com/flass/pantagruel">https://github.com/flass/pantagruel</jats:ext-link>.</jats:p>

Journal article

Lassalle F, Dastgheib SMM, Zhao F-J, Zhang J, Verbarg S, Frühling A, Brinkmann H, Osborne TH, Sikorski J, Balloux F, Didelot X, Santini JM, Petersen Jet al., 2019, Phylogenomic analysis reveals the basis of adaptation of Pseudorhizobium species to extreme environments

<jats:title>Abstract</jats:title><jats:p>The family <jats:italic>Rhizobiaceae</jats:italic> includes many genera of soil bacteria, often isolated for their association with plants. Herein, we investigate the genomic diversity of a group of <jats:italic>Rhizobium</jats:italic> species and unclassified strains isolated from atypical environments, including seawater, rock matrix or polluted soil. Based on whole-genome similarity and core genome phylogeny, we show that this group corresponds to the genus <jats:italic>Pseudorhizobium.</jats:italic> We thus reclassify <jats:italic>Rhizobium halotolerans, R. marinum, R. flavum</jats:italic> and <jats:italic>R. endolithicum</jats:italic> as <jats:italic>P. halotolerans</jats:italic> comb. nov., <jats:italic>P. marinum</jats:italic> comb. nov.<jats:italic>, P. flavum</jats:italic> comb. nov. and <jats:italic>R. endolithicum</jats:italic> comb. nov., respectively, and show that <jats:italic>P. pelagicum</jats:italic> is a synonym of <jats:italic>P. marinum</jats:italic>. We also delineate a new chemolithoautotroph species, <jats:italic>P. banfieldiae</jats:italic> sp. nov., whose type strain is NT-26<jats:sup>T</jats:sup> (= DSM 106348<jats:sup>T</jats:sup> = CFBP 8663<jats:sup>T</jats:sup>). This genome-based classification was supported by a chemotaxonomic comparison, with gradual taxonomic resolution provided by fatty acid, protein and metabolic profiles. In addition, we used a phylogenetic approach to infer scenarios of duplication, horizontal transfer and loss for all genes in the <jats:italic>Pseudorhizobium</jats:italic> pangenome. We thus identify the key functions associated with the diversification of each species and higher clades, shedding light on the mechanisms of adaptation to their respective ecological

Journal article

Criscuolo A, Issenhuth-Jeanjean S, Didelot X, Thorell K, Hale J, Parkhill J, Thomson NR, Weill F-X, Falush D, Brisse Set al., 2019, The speciation and hybridization history of the genus Salmonella, MICROBIAL GENOMICS, Vol: 5, ISSN: 2057-5858

Journal article

Volz EM, Wiuf C, Grad YH, Frost SDW, Dennis AM, Didelot Xet al., 2019, Identification of hidden population structure in time-scaled phylogenies, Publisher: Cold Spring Harbor Laboratory

<jats:title>Abstract</jats:title><jats:p>Population structure influences genealogical patterns, however data pertaining to how populations are structured are often unavailable or not directly observable. Inference of population structure is highly important in molecular epidemiology where pathogen phylogenetics is increasingly used to infer transmission patterns and detect outbreaks. Discrepancies between observed and idealised genealogies, such as those generated by the coalescent process, can be quantified, and where significant differences occur, may reveal the action of natural selection, host population structure, or other demographic and epidemiological heterogeneities. We have developed a fast non-parametric statistical test for detection of cryptic population structure in time-scaled phylogenetic trees. The test is based on contrasting estimated phylogenies with the theoretically expected phylodynamic ordering of common ancestors in two clades within a coalescent framework. These statistical tests have also motivated the development of algorithms which can be used to quickly screen a phylogenetic tree for clades which are likely to share a distinct demographic or epidemiological history. Epidemiological applications include identification of outbreaks in vulnerable host populations or rapid expansion of genotypes with a fitness advantage. To demonstrate the utility of these methods for outbreak detection, we applied the new methods to large phylogenies reconstructed from thousands of HIV-1 partial <jats:italic>pol</jats:italic> sequences. This revealed the presence of clades which had grown rapidly in the recent past, and was significantly concentrated in young men, suggesting recent and rapid transmission in that group. Furthermore, to demonstrate the utility of these methods for the study of antimicrobial resistance, we applied the new methods to a large phylogeny reconstructed from whole genome <jats:italic>Neisseria go

Working paper

Didelot X, Pouwels KB, 2019, Machine-learning-assisted selection of antibiotic prescription, NATURE MEDICINE, Vol: 25, Pages: 1033-1034, ISSN: 1078-8956

Journal article

Ozer EA, Nnah E, Didelot X, Whitaker RJ, Hauser ARet al., 2019, The Population Structure of Pseudomonas aeruginosa Is Characterized by Genetic Isolation of exoU plus and exoS plus Lineages, GENOME BIOLOGY AND EVOLUTION, Vol: 11, Pages: 1780-1796, ISSN: 1759-6653

Journal article

Ailloud F, Didelot X, Woltemate S, Pfaffinger G, Overmann J, Bader RC, Schulz C, Malfertheiner P, Suerbaum Set al., 2019, Within-host evolution of Helicobacter pylori shaped by niche-specific adaptation, intragastric migrations and selective sweeps, NATURE COMMUNICATIONS, Vol: 10, ISSN: 2041-1723

Journal article

Moniri A, Rodriguez-Manzano J, Malpartida-Cardenas K, Yu L-S, Didelot X, Holmes A, Georgiou Pet al., 2019, Framework for DNA quantification and outlier detection using multidimensional standard curves, Analytical Chemistry, Vol: 91, Pages: 7426-7434, ISSN: 0003-2700

Real-time PCR is a highly sensitive and powerful technology for the quantification of DNA and has become the method of choice in microbiology, bioengineering, and molecular biology. Currently, the analysis of real-time PCR data is hampered by only considering a single feature of the amplification profile to generate a standard curve. The current “gold standard” is the cycle-threshold (Ct) method which is known to provide poor quantification under inconsistent reaction efficiencies. Multiple single-feature methods have been developed to overcome the limitations of the Ct method; however, there is an unexplored area of combining multiple features in order to benefit from their joint information. Here, we propose a novel framework that combines existing standard curve methods into a multidimensional standard curve. This is achieved by considering multiple features together such that each amplification curve is viewed as a point in a multidimensional space. Contrary to only considering a single-feature, in the multidimensional space, data points do not fall exactly on the standard curve, which enables a similarity measure between amplification curves based on distances between data points. We show that this framework expands the capabilities of standard curves in order to optimize quantification performance, provide a measure of how suitable an amplification curve is for a standard, and thus automatically detect outliers and increase the reliability of quantification. Our aim is to provide an affordable solution to enhance existing diagnostic settings through maximizing the amount of information extracted from conventional instruments.

Journal article

Eyre DW, Didelot X, Buckley AM, Freeman J, Moura IB, Crook DW, Peto TEA, SarahWalker A, Wilcox MH, Dingle KEet al., 2019, Clostridium difficile trehalose metabolism variants are common and not associated with adverse patient outcomes when variably present in the same lineage, EBIOMEDICINE, Vol: 43, Pages: 347-355, ISSN: 2352-3964

Journal article

van Dorp L, Wang Q, Shaw LP, Acman M, Brynildsrud OB, Eldholm V, Wang R, Gao H, Yin Y, Chen H, Ding C, Farrer RA, Didelot X, Balloux F, Wang Het al., 2019, Rapid phenotypic evolution in multidrug-resistant Klebsiella pneumoniae hospital outbreak strains, MICROBIAL GENOMICS, Vol: 5, ISSN: 2057-5858

Journal article

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