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July 7, 2019  |  

Listeria monocytogenes in stone fruits linked to a multistate outbreak: enumeration of cells and whole-genome sequencing.

In 2014, the identification of stone fruits contaminated with Listeria monocytogenes led to the subsequent identification of a multistate outbreak. Simultaneous detection and enumeration of L. monocytogenes were performed on 105 fruits, each weighing 127 to 145 g, collected from 7 contaminated lots. The results showed that 53.3% of the fruits yielded L. monocytogenes (lower limit of detection, 5 CFU/fruit), and the levels ranged from 5 to 2,850 CFU/fruit, with a geometric mean of 11.3 CFU/fruit (0.1 CFU/g of fruit). Two serotypes, IVb-v1 and 1/2b, were identified by a combination of PCR- and antiserum-based serotyping among isolates from fruits and their packing environment; certain fruits contained a mixture of both serotypes. Single nucleotide polymorphism (SNP)-based whole-genome sequencing (WGS) analysis clustered isolates from two case-patients with the serotype IVb-v1 isolates and distinguished outbreak-associated isolates from pulsed-field gel electrophoresis (PFGE)-matched, but epidemiologically unrelated, clinical isolates. The outbreak-associated isolates differed by up to 42 SNPs. All but one serotype 1/2b isolate formed another WGS cluster and differed by up to 17 SNPs. Fully closed genomes of isolates from the stone fruits were used as references to maximize the resolution and to increase our confidence in prophage analysis. Putative prophages were conserved among isolates of each WGS cluster. All serotype IVb-v1 isolates belonged to singleton sequence type 382 (ST382); all but one serotype 1/2b isolate belonged to clonal complex 5.WGS proved to be an excellent tool to assist in the epidemiologic investigation of listeriosis outbreaks. The comparison at the genome level contributed to our understanding of the genetic diversity and variations among isolates involved in an outbreak or isolates associated with food and environmental samples from one facility. Fully closed genomes increased our confidence in the identification and comparison of accessory genomes. The diversity among the outbreak-associated isolates and the inclusion of PFGE-matched, but epidemiologically unrelated, isolates demonstrate the high resolution of WGS. The prevalence and enumeration data could contribute to our further understanding of the risk associated with Listeria monocytogenes contamination, especially among high-risk populations. Copyright © 2016 Chen et al.

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July 7, 2019  |  

Use of single molecule sequencing for comparative genomics of an environmental and a clinical isolate of Clostridium difficile ribotype 078.

How the pathogen Clostridium difficile might survive, evolve and be transferred between reservoirs within the natural environment is poorly understood. Some ribotypes are found both in clinical and environmental settings. Whether these strains are distinct from each another and evolve in the specific environments is not established. The possession of a highly mobile genome has contributed to the genetic diversity and ongoing evolution of C. difficile. Interpretations of genetic diversity have been limited by fragmented assemblies resulting from short-read length sequencing approaches and by a limited understanding of epigenetic regulation of diversity. To address this, single molecule real time (SMRT) sequencing was used in this study as it produces high quality genome sequences, with resolution of repeat regions (including those found in mobile elements) and can generate data to determine methylation modifications across the sequence (the methylome).Chromosomal rearrangements and ribosomal operon duplications were observed in both genomes. The rearrangements occurred at insertion sites within two mobile genetic elements (MGEs), Tn6164 and Tn6293, present only in the M120 and CD105HS27 genomes, respectively. The gene content of these two transposons differ considerably which could impact upon horizontal gene transfer; differences include CDSs encoding methylases and a conjugative prophage only in Tn6164. To investigate mechanisms which could affect MGE transfer, the methylome, restriction modification (RM)  and the CRISPR/Cas systems were characterised for each strain. Notably, the environmental isolate, CD105HS27, does not share a consensus motif for (m4)C methylation, but has one additional spacer  when compared to the clinical isolate M120.These findings show key differences between the two strains in terms of their genetic capacity for MGE transfer. The carriage of horizontally transferred genes appear to have genome wide effects based on two different methylation patterns. The CRISPR/Cas system appears active although perhaps slow to evolve. Data suggests that both mechanisms are functional and impact upon horizontal gene transfer and genome evolution within C. difficile.

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July 7, 2019  |  

Complete genome sequence of the freshwater bacterium Beggiatoa leptomitoformis strain D-401.

Here, we report the complete closed genome sequence and methylome analysis of Beggiatoa leptomitoformis strain D-401 (DSM 14945, UNIQEMU 779), which is quite different from the previously described Beggiatoa leptomitoformis neotype strain D-402T (DSM 14946, UNIQEM U 779) with regard to morphology and lithotrophic growth in the presence of thiosulfate. Copyright © 2018 Fomenkov et al.

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July 7, 2019  |  

Comparative genomic analysis of Staphylococcus lugdunensis shows a closed pan-genome and multiple barriers to horizontal gene transfer.

Coagulase negative staphylococci (CoNS) are commensal bacteria on human skin. Staphylococcus lugdunensis is a unique CoNS which produces various virulence factors and may, like S. aureus, cause severe infections, particularly in hospital settings. Unlike other staphylococci, it remains highly susceptible to antimicrobials, and genome-based phylogenetic studies have evidenced a highly conserved genome that distinguishes it from all other staphylococci.We demonstrate that S. lugdunensis possesses a closed pan-genome with a very limited number of new genes, in contrast to other staphylococci that have an open pan-genome. Whole-genome nucleotide and amino acid identity levels are also higher than in other staphylococci. We identified numerous genetic barriers to horizontal gene transfer that might explain this result. The S. lugdunensis genome has multiple operons encoding for restriction-modification, CRISPR/Cas and toxin/antitoxin systems. We also identified a new PIN-like domain-associated protein that might belong to a larger operon, comprising a metalloprotease, that could function as a new toxin/antitoxin or detoxification system.We show that S. lugdunensis has a unique genome profile within staphylococci, with a closed pan-genome and several systems to prevent horizontal gene transfer. Its virulence in clinical settings does not rely on its ability to acquire and exchange antibiotic resistance genes or other virulence factors as shown for other staphylococci.

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July 7, 2019  |  

Complete genome sequence of Lactococcus lactis subsp. lactis SLPE1-3, a novel lactic acid bacterium causing postharvest decay of the mushroom Pleurotus eryngii

Lactococcus lactis subsp. lactis is a pathogenic bacterium causing postharvest decay of the cultivated mushroom Pleurotus eryngii, whose pathogenic mechanism is little known. Sequencing of its complete genome is a prerequisite for revealing the molecular mechanism of infection. In this research, the complete genome of SLPE1-3 was obtained using the Single Molecular Real Time (SMRT) sequencing strategy. The genome was analyzed both structurally and functionally. The complete genome of SLPE1-3 consists of a single, circular chromosome (2,522,493 bp; 34.91% GC content) without any plasmid. The results showed the feasibility and superiority of SMRT in bacterial complete-genome research. The genome of SLPE1-3 has the specific features of L. lactis subsp. lactis not just in the phylogenesis and genome structure, but also in functional classification. Compared with L. lactis subsp. lactis IL1403, L. lactis subsp. cremoris MG1363 and L. lactis subsp. lactis KF147, 23 peculiar genes were identified in SLPE1-3 which were involved in lipid metabolism, cell wall biogenesis and some functional enzymes. In addition, 37 potential genes relating to antifungal function were filtered for further mechanism research.

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July 7, 2019  |  

Complete genome sequences of two Rhodobacter strains.

We report the complete genome sequences of two strains of the Alphaproteobacteria genus Rhodobacter, Rhodobacter blasticus 28/5, the source of the commercially available enzyme RsaI, and a new isolate of Rhodobacter sphaeroides 2.4.1. Both strains contain multiple restriction-modification systems, and their DNA methylation motifs are included in this report.

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