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July 7, 2019

Seeking the source of Pseudomonas aeruginosa infections in a recently opened hospital: an observational study using whole-genome sequencing.

Pseudomonas aeruginosa is a common nosocomial pathogen responsible for significant morbidity and mortality internationally. Patients may become colonised or infected with P. aeruginosa after exposure to contaminated sources within the hospital environment. The aim of this study was to determine whether whole-genome sequencing (WGS) can be used to determine the source in a cohort of burns patients at high risk of P. aeruginosa acquisition.An observational prospective cohort study.Burns care ward and critical care ward in the UK.Patients with >7% total burns by surface area were recruited into the study.All patients were screened for P. aeruginosa on admission and samples taken from their immediate environment, including water. Screening patients who subsequently developed a positive P. aeruginosa microbiology result were subject to enhanced environmental surveillance. All isolates of P. aeruginosa were genome sequenced. Sequence analysis looked at similarity and relatedness between isolates.WGS for 141 P. aeruginosa isolates were obtained from patients, hospital water and the ward environment. Phylogenetic analysis revealed eight distinct clades, with a single clade representing the majority of environmental isolates in the burns unit. Isolates from three patients had identical genotypes compared with water isolates from the same room. There was clear clustering of water isolates by room and outlet, allowing the source of acquisitions to be unambiguously identified. Whole-genome shotgun sequencing of biofilm DNA extracted from a thermostatic mixer valve revealed this was the source of a P. aeruginosa subpopulation previously detected in water. In the remaining two cases there was no clear link to the hospital environment.This study reveals that WGS can be used for source tracking of P. aeruginosa in a hospital setting, and that acquisitions can be traced to a specific source within a hospital ward. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

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July 7, 2019

Bacillary dysentery from World War 1 and NCTC1, the first bacterial isolate in the National Collection.

In early 1915, a 28-year-old man arrived at No 14 Stationary Hospital in Wimereux, France. Although no clinical records remain, we believe he would have presented with bloody diarrhoea and severe abdominal cramping, and he was diagnosed with dysentery. On March 13, 1915, the patient, who we believe was Private Ernest Cable of the 2nd Battalion of the East Surrey Regiment (appendix), died. Lieutenant William Broughton-Alcock, whose military records1 identify him as a bacteriologist for No 14 Stationary Hospital, collected this isolate—later identified as a Shigella flexneri serotype 2a bacterium—which was the first bacterial isolate deposited in the UK National Collection of Type Cultures (NCTC)2 using the original isolate name Cable.

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July 7, 2019

Draft genome sequence of Pantoea agglomerans R190, a producer of antibiotics against phytopathogens and foodborne pathogens.

Pantoea agglomerans R190, isolated from an apple orchard, showed antibacterial activity against various spoilage bacteria, including Pectobacterium carotovorum subsp. carotovorum, and foodborne pathogens such as Escherichia coli O157:H7. Here, we report the genome sequence of P. agglomerans R190. This report will raise the value of P. agglomerans as an agent for biocontrol of disease. Copyright © 2014. Published by Elsevier B.V.

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July 7, 2019

Genome sequencing of an extended series of NDM-producing Klebsiella pneumoniae isolates from Neonatal infections in a Nepali hospital characterizes the extent of community- versus hospital-associated transmission in an endemic setting.

NDM-producing Klebsiella pneumoniae strains represent major clinical and infection control challenges, particularly in resource-limited settings with high rates of antimicrobial resistance. Determining whether transmission occurs at a gene, plasmid, or bacterial strain level and within hospital and/or the community has implications for monitoring and controlling spread. Whole-genome sequencing (WGS) is the highest-resolution typing method available for transmission epidemiology. We sequenced carbapenem-resistant K. pneumoniae isolates from 26 individuals involved in several infection case clusters in a Nepali neonatal unit and 68 other clinical Gram-negative isolates from a similar time frame, using Illumina and PacBio technologies. Within-outbreak chromosomal and closed-plasmid structures were generated and used as data set-specific references. Three temporally separated case clusters were caused by a single NDM K. pneumoniae strain with a conserved set of four plasmids, one being a 304,526-bp plasmid carrying blaNDM-1. The plasmids contained a large number of antimicrobial/heavy metal resistance and plasmid maintenance genes, which may have explained their persistence. No obvious environmental/human reservoir was found. There was no evidence of transmission of outbreak plasmids to other Gram-negative clinical isolates, although blaNDM variants were present in other isolates in different genetic contexts. WGS can effectively define complex antimicrobial resistance epidemiology. Wider sampling frames are required to contextualize outbreaks. Infection control may be effective in terminating outbreaks caused by particular strains, even in areas with widespread resistance, although this study could not demonstrate evidence supporting specific interventions. Larger, detailed studies are needed to characterize resistance genes, vectors, and host strains involved in disease, to enable effective intervention. Copyright © 2014 Stoesser et al.

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July 7, 2019

Diversification of bacterial genome content through distinct mechanisms over different timescales.

Bacterial populations often consist of multiple co-circulating lineages. Determining how such population structures arise requires understanding what drives bacterial diversification. Using 616 systematically sampled genomes, we show that Streptococcus pneumoniae lineages are typically characterized by combinations of infrequently transferred stable genomic islands: those moving primarily through transformation, along with integrative and conjugative elements and phage-related chromosomal islands. The only lineage containing extensive unique sequence corresponds to a set of atypical unencapsulated isolates that may represent a distinct species. However, prophage content is highly variable even within lineages, suggesting frequent horizontal transmission that would necessitate rapidly diversifying anti-phage mechanisms to prevent these viruses sweeping through populations. Correspondingly, two loci encoding Type I restriction-modification systems able to change their specificity over short timescales through intragenomic recombination are ubiquitous across the collection. Hence short-term pneumococcal variation is characterized by movement of phage and intragenomic rearrangements, with the slower transfer of stable loci distinguishing lineages.

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July 7, 2019

Sequence-dependent elongation dynamics on macrolide-bound ribosomes.

The traditional view of macrolide antibiotics as plugs inside the ribosomal nascent peptide exit tunnel (NPET) has lately been challenged in favor of a more complex, heterogeneous mechanism, where drug-peptide interactions determine the fate of a translating ribosome. To investigate these highly dynamic processes, we applied single-molecule tracking of elongating ribosomes during inhibition of elongation by erythromycin of several nascent chains, including ErmCL and H-NS, which were shown to be, respectively, sensitive and resistant to erythromycin. Peptide sequence-specific changes were observed in translation elongation dynamics in the presence of a macrolide-obstructed NPET. Elongation rates were not severely inhibited in general by the presence of the drug; instead, stalls or pauses were observed as abrupt events. The dynamic pathways of nascent-chain-dependent elongation pausing in the presence of macrolides determine the fate of the translating ribosome stalling or readthrough. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

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July 7, 2019

Genome sequences of Vibrio navarrensis, a potential human pathogen.

Vibrio navarrensis is an aquatic bacterium recently shown to be associated with human illness. We report the first genome sequences of three V. navarrensis strains obtained from clinical and environmental sources. Preliminary analyses of the sequences reveal that V. navarrensis contains genes commonly associated with virulence in other human pathogens. Copyright © 2014 Gladney et al.

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July 7, 2019

Pilon: an integrated tool for comprehensive microbial variant detection and genome assembly improvement.

Advances in modern sequencing technologies allow us to generate sufficient data to analyze hundreds of bacterial genomes from a single machine in a single day. This potential for sequencing massive numbers of genomes calls for fully automated methods to produce high-quality assemblies and variant calls. We introduce Pilon, a fully automated, all-in-one tool for correcting draft assemblies and calling sequence variants of multiple sizes, including very large insertions and deletions. Pilon works with many types of sequence data, but is particularly strong when supplied with paired end data from two Illumina libraries with small e.g., 180 bp and large e.g., 3-5 Kb inserts. Pilon significantly improves draft genome assemblies by correcting bases, fixing mis-assemblies and filling gaps. For both haploid and diploid genomes, Pilon produces more contiguous genomes with fewer errors, enabling identification of more biologically relevant genes. Furthermore, Pilon identifies small variants with high accuracy as compared to state-of-the-art tools and is unique in its ability to accurately identify large sequence variants including duplications and resolve large insertions. Pilon is being used to improve the assemblies of thousands of new genomes and to identify variants from thousands of clinically relevant bacterial strains. Pilon is freely available as open source software.

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July 7, 2019

Simultaneous sequencing of oxidized methylcytosines produced by TET/JBP dioxygenases in Coprinopsis cinerea.

TET/JBP enzymes oxidize 5-methylpyrimidines in DNA. In mammals, the oxidized methylcytosines (oxi-mCs) function as epigenetic marks and likely intermediates in DNA demethylation. Here we present a method based on diglucosylation of 5-hydroxymethylcytosine (5hmC) to simultaneously map 5hmC, 5-formylcytosine, and 5-carboxylcytosine at near-base-pair resolution. We have used the method to map the distribution of oxi-mC across the genome of Coprinopsis cinerea, a basidiomycete that encodes 47 TET/JBP paralogs in a previously unidentified class of DNA transposons. Like 5-methylcytosine residues from which they are derived, oxi-mC modifications are enriched at centromeres, TET/JBP transposons, and multicopy paralogous genes that are not expressed, but rarely mark genes whose expression changes between two developmental stages. Our study provides evidence for the emergence of an epigenetic regulatory system through recruitment of selfish elements in a eukaryotic lineage, and describes a method to map all three different species of oxi-mCs simultaneously.

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July 7, 2019

Draft genome sequences of Escherichia coli strains isolated from septic patients.

We present the draft genome sequences of six strains of Escherichia coli isolated from blood cultures collected from patients with sepsis. The strains were collected from two patient sets, those with a high severity of illness, and those with a low severity of illness. Each genome was sequenced by both Illumina and PacBio for comparison. Copyright © 2014 Dunitz et al.

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July 7, 2019

ProbAlign: a re-alignment method for long sequencing reads

The incorrect alignments are a severe problem in variant calling, and remain as a challenge computational issue in Bioinformatics field. Although there have been some methods utilizing the re-alignment approach to tackle the misalignments, a standalone re-alignment tool for long sequencing reads is lacking. Hence, we present a standalone tool to correct the misalignments, called ProbAlign. It can be integrated into the pipelines of not only variant calling but also other genomic applications. We demonstrate the use of re-alignment in two diverse and important genomics fields: variant calling and viral quasispecies reconstruction. First, variant calling results in the Pacific Biosciences SMRT re-sequencing data of NA12878 show that false positives can be reduced by 43.5%, and true positives can be increased by 24.8% averagely, after re-alignment. Second, results in reconstructing a 5-virus-mix show that the viral population can be completely unraveled, and also the estimation of quasispecies frequencies has been improved, after re-alignment. ProbAlign is freely available in the PyroTools toolkit (https://github.com/homopolymer/PyroTools).

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July 7, 2019

The Harvest suite for rapid core-genome alignment and visualization of thousands of intraspecific microbial genomes.

Whole-genome sequences are now available for many microbial species and clades, however, existing whole-genome alignment methods are limited in their ability to perform sequence comparisons of multiple sequences simultaneously. Here we present the Harvest suite of core-genome alignment and visualization tools for the rapid and simultaneous analysis of thousands of intraspecific microbial strains. Harvest includes Parsnp, a fast core-genome multi-aligner, and Gingr, a dynamic visual platform. Together they provide interactive core-genome alignments, variant calls, recombination detection, and phylogenetic trees. Using simulated and real data we demonstrate that our approach exhibits unrivaled speed while maintaining the accuracy of existing methods. The Harvest suite is open-source and freely available from: http://github.com/marbl/harvest.

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