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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

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

Complete genome sequence of the lignin-degrading bacterium Klebsiella sp. strain BRL6-2.

In an effort to discover anaerobic bacteria capable of lignin degradation, we isolated Klebsiella sp. strain BRL6-2 on minimal media with alkali lignin as the sole carbon source. This organism was isolated anaerobically from tropical forest soils collected from the Bisley watershed at the Ridge site in the El Yunque National Forest in Puerto Rico, USA, part of the Luquillo Long-Term Ecological Research Station. At this site, the soils experience strong fluctuations in redox potential and are characterized by cycles of iron oxidation and reduction. Genome sequencing was targeted because of its ability to grow on lignin anaerobically and lignocellulolytic activity via in vitro enzyme assays. The genome of Klebsiella sp. strain BRL6-2 is 5.80 Mbp with no detected plasmids, and includes a relatively small arsenal of genes encoding lignocellulolytic carbohydrate active enzymes. The genome revealed four putative peroxidases including glutathione and DyP-type peroxidases, and a complete protocatechuate pathway encoded in a single gene cluster. Physiological studies revealed Klebsiella sp. strain BRL6-2 to be relatively stress tolerant to high ionic strength conditions. It grows in increasing concentrations of ionic liquid (1-ethyl-3-methyl-imidazolium acetate) up to 73.44 mM and NaCl up to 1.5 M.

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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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July 7, 2019

Dissemination of cephalosporin resistance genes between Escherichia coli strains from farm animals and humans by specific plasmid lineages.

Third-generation cephalosporins are a class of ß-lactam antibiotics that are often used for the treatment of human infections caused by Gram-negative bacteria, especially Escherichia coli. Worryingly, the incidence of human infections caused by third-generation cephalosporin-resistant E. coli is increasing worldwide. Recent studies have suggested that these E. coli strains, and their antibiotic resistance genes, can spread from food-producing animals, via the food-chain, to humans. However, these studies used traditional typing methods, which may not have provided sufficient resolution to reliably assess the relatedness of these strains. We therefore used whole-genome sequencing (WGS) to study the relatedness of cephalosporin-resistant E. coli from humans, chicken meat, poultry and pigs. One strain collection included pairs of human and poultry-associated strains that had previously been considered to be identical based on Multi-Locus Sequence Typing, plasmid typing and antibiotic resistance gene sequencing. The second collection included isolates from farmers and their pigs. WGS analysis revealed considerable heterogeneity between human and poultry-associated isolates. The most closely related pairs of strains from both sources carried 1263 Single-Nucleotide Polymorphisms (SNPs) per Mbp core genome. In contrast, epidemiologically linked strains from humans and pigs differed by only 1.8 SNPs per Mbp core genome. WGS-based plasmid reconstructions revealed three distinct plasmid lineages (IncI1- and IncK-type) that carried cephalosporin resistance genes of the Extended-Spectrum Beta-Lactamase (ESBL)- and AmpC-types. The plasmid backbones within each lineage were virtually identical and were shared by genetically unrelated human and animal isolates. Plasmid reconstructions from short-read sequencing data were validated by long-read DNA sequencing for two strains. Our findings failed to demonstrate evidence for recent clonal transmission of cephalosporin-resistant E. coli strains from poultry to humans, as has been suggested based on traditional, low-resolution typing methods. Instead, our data suggest that cephalosporin resistance genes are mainly disseminated in animals and humans via distinct plasmids.

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July 7, 2019

Finished bacterial genomes from shotgun sequence data.

Exceptionally accurate genome reference sequences have proven to be of great value to microbial researchers. Thus, to date, about 1800 bacterial genome assemblies have been “finished” at great expense with the aid of manual laboratory and computational processes that typically iterate over a period of months or even years. By applying a new laboratory design and new assembly algorithm to 16 samples, we demonstrate that assemblies exceeding finished quality can be obtained from whole-genome shotgun data and automated computation. Cost and time requirements are thus dramatically reduced.

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July 7, 2019

Genomic epidemiology of the Escherichia coli O104:H4 outbreaks in Europe, 2011.

The degree to which molecular epidemiology reveals information about the sources and transmission patterns of an outbreak depends on the resolution of the technology used and the samples studied. Isolates of Escherichia coli O104:H4 from the outbreak centered in Germany in May-July 2011, and the much smaller outbreak in southwest France in June 2011, were indistinguishable by standard tests. We report a molecular epidemiological analysis using multiplatform whole-genome sequencing and analysis of multiple isolates from the German and French outbreaks. Isolates from the German outbreak showed remarkably little diversity, with only two single nucleotide polymorphisms (SNPs) found in isolates from four individuals. Surprisingly, we found much greater diversity (19 SNPs) in isolates from seven individuals infected in the French outbreak. The German isolates form a clade within the more diverse French outbreak strains. Moreover, five isolates derived from a single infected individual from the French outbreak had extremely limited diversity. The striking difference in diversity between the German and French outbreak samples is consistent with several hypotheses, including a bottleneck that purged diversity in the German isolates, variation in mutation rates in the two E. coli outbreak populations, or uneven distribution of diversity in the seed populations that led to each outbreak.

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July 7, 2019

Direct sequencing of small genomes on the Pacific Biosciences RS without library preparation.

We have developed a sequencing method on the Pacific Biosciences RS sequencer (the PacBio) for small DNA molecules that avoids the need for a standard library preparation. To date this approach has been applied toward sequencing single-stranded and double-stranded viral genomes, bacterial plasmids, plasmid vector models for DNA-modification analysis, and linear DNA fragments covering an entire bacterial genome. Using direct sequencing it is possible to generate sequence data from as little as 1 ng of DNA, offering a significant advantage over current protocols which typically require 400-500 ng of sheared DNA for the library preparation.

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July 7, 2019

The complete genome sequence of Cronobacter sakazakii ATCC 29544(T), a food-borne pathogen, isolated from a child’s throat.

Cronobacter sakazakii is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of severe diseases: meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. However, the pathogenesis mechanism of this pathogen remains largely unknown. To determine its pathogenesis at the genomic level, the genome of C. sakazakii ATCC 29544(T) was completely sequenced and analyzed.The genomic DNA, containing a circular chromosome and three plasmids, is composed of 4,511,265 bp with a GC content of 56.71%, containing 4380 predicted open reading frames (ORFs), 22 rRNA genes, and 83 tRNA genes. The plasmids, designated pCSK29544_p1, pCSK29544_p2, and pCSK29544_p3, were 93,905-bp, 4938-bp, and 53,457-bp with GC contents of 57.02, 54.88, and 50.07%, respectively. They were also predicted to have 72, 6, and 57 ORFs without RNA genes.The strain ATCC 29544(T) genome has ompA and ibeB-homologous cusC genes, probably associated with the invasion of human brain microvascular endothelial cells (BMECs). In addition, gene clusters for siderophore production (iucABCD/iutA) and the related transport system (eitCBAD) were detected in pCSK29544_p1 plasmid, indicating better iron uptake ability for survival. Furthermore, to survive under extremely dry condition like milk powder, this genome has gene clusters for biosynthesis of capsular proteins (CSK29544_00281-00284) and cellulose (CSK29544_01124-01127) for biofilm formation and a gene cluster for utilization of sialic acid in the milk (nanKTAR). The genome information of C. sakazakii ATCC 29544(T) would provide further understanding of its pathogenesis at the molecular level for the regulation of pathogenicity and the development of a rapid detection method using biomarkers.

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July 7, 2019

The secondary resistome of multidrug-resistant Klebsiella pneumoniae.

Klebsiella pneumoniae causes severe lung and bloodstream infections that are difficult to treat due to multidrug resistance. We hypothesized that antimicrobial resistance can be reversed by targeting chromosomal non-essential genes that are not responsible for acquired resistance but essential for resistant bacteria under therapeutic concentrations of antimicrobials. Conditional essentiality of individual genes to antimicrobial resistance was evaluated in an epidemic multidrug-resistant clone of K. pneumoniae (ST258). We constructed a high-density transposon mutant library of >430,000 unique Tn5 insertions and measured mutant depletion upon exposure to three clinically relevant antimicrobials (colistin, imipenem or ciprofloxacin) by Transposon Directed Insertion-site Sequencing (TraDIS). Using this high-throughput approach, we defined three sets of chromosomal non-essential genes essential for growth during exposure to colistin (n?=?35), imipenem (n?=?1) or ciprofloxacin (n?=?1) in addition to known resistance determinants, collectively termed the “secondary resistome”. As proof of principle, we demonstrated that inactivation of a non-essential gene not previously found linked to colistin resistance (dedA) restored colistin susceptibility by reducing the minimum inhibitory concentration from 8 to 0.5?µg/ml, 4-fold below the susceptibility breakpoint (S?=?2?µg/ml). This finding suggests that the secondary resistome is a potential target for developing antimicrobial “helper” drugs that restore the efficacy of existing antimicrobials.

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July 7, 2019

Prevalence of mcr-1 in Escherichia coli and Klebsiella pneumoniae recovered from bloodstream infections in China: a multicentre longitudinal study.

Polymyxin antibiotics are used as last-resort therapies to treat infections caused by multidrug-resistant Gram-negative bacteria. The plasmid-mediated colistin resistance determinant MCR-1 has been identified in Enterobacteriaceae in China. We did this study to investigate the prevalence of the mcr-1 gene in clinical isolates from patients with bloodstream infections in China.Clinical isolates of Escherichia coli and Klebsiella pneumoniae were collected from patients with bloodstream infections at 28 hospitals in China, then screened for colistin resistance by broth microdilution and for the presence of the mcr-1 gene by PCR amplification. We subjected mcr-1-positive isolates to genotyping, susceptibility testing, and clinical data analysis. We established the genetic location of mcr-1 with Southern blot hybridisation, and we analysed plasmids containing mcr-1 with filter mating, electroporation, and DNA sequencing.2066 isolates, consisting of 1495 E coli isolates and 571 K pneumoniae isolates were collected. Of the 1495 E coli isolates, 20 (1%) were mcr-1-positive, whereas we detected only one (<1%) mcr-1-positive isolate among the 571 K pneumoniae isolates. All mcr-1-positive E coli and K pneumoniae isolates were resistant to colistin, with minimum inhibitory concentrations values in the range of 4-32 mg/L, except for one E coli isolate that had a minimum inhibitory concentration less than or equal to 0·06 mg/L. All 21 mcr-1-positive isolates were susceptible to tigecycline and 20 isolates (95%) were susceptible to the carbapenem and ß-lactamase inhibitor combination piperacillin and tazobactam. One mcr-1-positive E coli isolate also produced NDM-5, which confers resistance to beta-lactam antibiotics. The 21 mcr-1-positive isolates were clonally diverse and carried mcr-1 on two types of plasmids, a 33 kb IncX4 plasmid and a 61 kb Inc12 plasmid. The 30 day mortality of the patients with bloodstream infections caused by mcr-1-positive isolates was zero.mcr-1-positive isolates from bloodstream infections were rare, sporadic, and remained susceptible to many antimicrobial agents. E coli, rather than K pneumoniae, was the main host of the mcr-1 gene. Further studies are needed to clarify the clinical impact of this novel resistance gene.National Natural Science Foundation of China. Copyright © 2017 Elsevier Ltd. All rights reserved.

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July 7, 2019

Coexistence of blaOXA-48 and truncated blaNDM-1 on different plasmids in a Klebsiella pneumoniae isolate in China.

Objectives: To describe the genetic environment, transferability, and antibiotic susceptibility of one clinical Klebsiella pneumoniae isolate harboring both blaOXA-48 and blaNDM-1 on different plasmids from a Chinese hospital. Methods: The isolate was subjected to antimicrobial susceptibility testing and multilocus sequence typing using Etest and PCR. The plasmids harboring blaOXA-48 and blaNDM-1 were analyzed through conjugation experiments, S1-nuclease pulsed-field gel electrophoresis, and hybridization with specific probes. Plasmid DNA was sequenced using Pacbio RS II and annotated using RAST. Results:K. pneumoniae RJ119, carrying both blaOXA-48 and blaNDM-1, was resistant to almost all carbapenems, cephalosporins, fluoroquinolone, and aminoglycosides and belonged to ST307. blaOXA-48 was located on a 61,748-bp IncL/M conjugative plasmid, which displayed overall nucleotide identity (99%) to pKPN-E1-Nr.7. blaNDM-1 was located on a 335,317-bp conjugative plasmid, which was a fusion of a blaNDM-1-harboring InA/C plasmid pNDM-US (140,825 bp, 99% identity) and an IncFIB plasmid pKPN-c22 (178,563 bp, 99% identity). The transconjugant RJ119-1 harboring blaNDM-1 was susceptible to carbapenem, and there was an insertion of IS10 into the blaNDM-1 gene. Conclusion: This is the first report of the coexistence of blaOXA-48 and blaNDM-1 in one K. pneumoniae clinical isolate in China. OXA-48 in RJ119 contributed to the majority to its high resistance to carbapenems, whereas NDM-1 remained unexpressed, most likely due to the insertion of IS10. Our results provide new insight for the relationship between genetic diagnosis and clinical treatment. They also indicate that increased surveillance of blaOXA-48 is urgently needed in China.

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