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Tuesday, April 21, 2020

Plasmid-encoded tet(X) genes that confer high-level tigecycline resistance in Escherichia coli.

Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant Gram-negative and Gram-positive bacteria1. Tigecycline resistance has sporadically occurred in recent years, primarily due to chromosome-encoding mechanisms, such as overexpression of efflux pumps and ribosome protection2,3. Here, we report the emergence of the plasmid-mediated mobile tigecycline resistance mechanism Tet(X4) in Escherichia coli isolates from China, which is capable of degrading all tetracyclines, including tigecycline and the US FDA newly approved eravacycline. The tet(X4)-harbouring IncQ1 plasmid is highly transferable, and can be successfully mobilized and stabilized in recipient clinical and laboratory strains of Enterobacteriaceae bacteria. It…

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Tuesday, April 21, 2020

Detection of transferable oxazolidinone resistance determinants in Enterococcus faecalis and Enterococcus faecium of swine origin in Sichuan Province, China.

The aim of this study was to detect the transferable oxazolidinone resistance determinants (cfr, optrA and poxtA) in E. faecalis and E. faecium of swine origin in Sichuan Province, China.A total of 158 enterococci strains (93 E. faecalis and 65 E. faecium) isolated from 25 large-scale swine farms were screened for the presence of cfr, optrA and poxtA by PCR. The genetic environments of cfr, optrA and poxtA were characterized by whole genome sequencing. Transfer of oxazolidinone resistance determinants was determined by conjugation or electrotransformation experiments.The transferable oxazolidinone resistance determinants, cfr, optrA and poxtA, were detected in zero, six, and…

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Tuesday, April 21, 2020

The genomic architecture of introgression among sibling species of bacteria

Gene transfer between bacterial species is an important mechanism for adaptation. For example, sets of genes that confer the ability to form nitrogen-fixing root nodules on host plants have frequently moved between Rhizobium species. It is not clear, though, whether such transfer is exceptional, or if frequent inter-species introgression is typical. To address this, we sequenced the genomes of 196 isolates of the Rhizobium leguminosarum species complex obtained from root nodules of white clover (Trifolium repens). Core gene phylogeny placed the isolates into five distinct genospecies that show high intra-genospecies recombination rates and remarkably different demographic histories. Most gene phylogenies…

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Tuesday, April 21, 2020

Advantage of the F2:A1:B- IncF Pandemic Plasmid over IncC Plasmids in In Vitro Acquisition and Evolution of blaCTX-M Gene-Bearing Plasmids in Escherichia coli.

Despite a fitness cost imposed on bacterial hosts, large conjugative plasmids play a key role in the diffusion of resistance determinants, such as CTX-M extended-spectrum ß-lactamases. Among the large conjugative plasmids, IncF plasmids are the most predominant group, and an F2:A1:B- IncF-type plasmid encoding a CTX-M-15 variant was recently described as being strongly associated with the emerging worldwide Escherichia coli sequence type 131 (ST131)-O25b:H4 H30Rx/C2 sublineage. In this context, we investigated the fitness cost of narrow-range F-type plasmids, including the F2:A1:B- IncF-type CTX-M-15 plasmid, and of broad-range C-type plasmids in the K-12-like J53-2 E. coli strain. Although all plasmids imposed…

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Tuesday, April 21, 2020

Klebsiella quasipneumoniae Provides a Window into Carbapenemase Gene Transfer, Plasmid Rearrangements, and Patient Interactions with the Hospital Environment.

Several emerging pathogens have arisen as a result of selection pressures exerted by modern health care. Klebsiella quasipneumoniae was recently defined as a new species, yet its prevalence, niche, and propensity to acquire antimicrobial resistance genes are not fully described. We have been tracking inter- and intraspecies transmission of the Klebsiella pneumoniae carbapenemase (KPC) gene, blaKPC, between bacteria isolated from a single institution. We applied a combination of Illumina and PacBio whole-genome sequencing to identify and compare K. quasipneumoniae from patients and the hospital environment over 10- and 5-year periods, respectively. There were 32 blaKPC-positive K. quasipneumoniae isolates, all of…

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Tuesday, April 21, 2020

Spreading Patterns of NDM-Producing Enterobacteriaceae in Clinical and Environmental Settings in Yangon, Myanmar.

The spread of carbapenemase-producing Enterobacteriaceae (CPE), contributing to widespread carbapenem resistance, has become a global concern. However, the specific dissemination patterns of carbapenemase genes have not been intensively investigated in developing countries, including Myanmar, where NDM-type carbapenemases are spreading in clinical settings. In the present study, we phenotypically and genetically characterized 91 CPE isolates obtained from clinical (n = 77) and environmental (n = 14) samples in Yangon, Myanmar. We determined the dissemination of plasmids harboring genes encoding NDM-1 and its variants using whole-genome sequencing and plasmid analysis. IncFII plasmids harboring blaNDM-5 and IncX3 plasmids harboring blaNDM-4 or blaNDM-7 were…

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Tuesday, April 21, 2020

Genetic variation in the conjugative plasmidome of a hospital effluent multidrug resistant Escherichia coli strain.

Bacteria harboring conjugative plasmids have the potential for spreading antibiotic resistance through horizontal gene transfer. It is described that the selection and dissemination of antibiotic resistance is enhanced by stressors, like metals or antibiotics, which can occur as environmental contaminants. This study aimed at unveiling the composition of the conjugative plasmidome of a hospital effluent multidrug resistant Escherichia coli strain (H1FC54) under different mating conditions. To meet this objective, plasmid pulsed field gel electrophoresis, optical mapping analyses and DNA sequencing were used in combination with phenotype analysis. Strain H1FC54 was observed to harbor five plasmids, three of which were conjugative…

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Tuesday, April 21, 2020

Transmission of ESBL-producing Escherichia coli between broilers and humans on broiler farms.

ESBL and AmpC ß-lactamases are an increasing concern for public health. Studies suggest that ESBL/pAmpC-producing Escherichia coli and their plasmids carrying antibiotic resistance genes can spread from broilers to humans working or living on broiler farms. These studies used traditional typing methods, which may not have provided sufficient resolution to reliably assess the relatedness of these isolates.Eleven suspected transmission events among broilers and humans living/working on eight broiler farms were investigated using whole-genome short-read (Illumina) and long-read sequencing (PacBio). Core genome MLST (cgMLST) was performed to investigate the occurrence of strain transmission. Horizontal plasmid and gene transfer were analysed using…

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Tuesday, April 21, 2020

Nodule bacteria from the cultured legume Phaseolus dumosus (belonging to the Phaseolus vulgaris cross-inoculation group) with common tropici phenotypic characteristics and symbiovar but distinctive phylogenomic position and chromid.

Phaseolus dumosus is an endemic species from mountain tops in Mexico that was found in traditional agriculture areas in Veracruz, Mexico. P. dumosus plants were identified by ITS sequences and their nodules were collected from agricultural fields or from trap plant experiments in the laboratory. Bacteria from P. dumosus nodules were identified as belonging to the phaseoli-etli-leguminosarum (PEL) or to the tropici group by 16S rRNA gene sequences. We obtained complete closed genomes from two P. dumosus isolates CCGE531 and CCGE532 that were phylogenetically placed within the tropici group but with a distinctive phylogenomic position and low average nucleotide identity…

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Tuesday, April 21, 2020

Toxin and genome evolution in a Drosophila defensive symbiosis.

Defenses conferred by microbial symbionts play a vital role in the health and fitness of their animal hosts. An important outstanding question in the study of defensive symbiosis is what determines long term stability and effectiveness against diverse natural enemies. In this study, we combine genome and transcriptome sequencing, symbiont transfection and parasite protection experiments, and toxin activity assays to examine the evolution of the defensive symbiosis between Drosophila flies and their vertically transmitted Spiroplasma bacterial symbionts, focusing in particular on ribosome-inactivating proteins (RIPs), symbiont-encoded toxins that have been implicated in protection against both parasitic wasps and nematodes. Although many…

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Tuesday, April 21, 2020

Dissemination of multiple carbapenem resistance genes in an in vitro gut model simulating the human colon.

Carbapenemase-producing Enterobacteriaceae (CPE) pose a major global health risk. Mobile genetic elements account for much of the increasing CPE burden.To investigate CPE colonization and the impact of antibiotic exposure on subsequent resistance gene dissemination within the gut microbiota using a model to simulate the human colon.Gut models seeded with CPE-negative human faeces [screened with BioMérieux chromID® CARBA-SMART (Carba-Smart), Cepheid Xpert® Carba-R assay (XCR)] were inoculated with distinct carbapenemase-producing Klebsiella pneumoniae strains (KPC, NDM) and challenged with imipenem or piperacillin/tazobactam then meropenem. Resistant populations were enumerated daily on selective agars (Carba-Smart); CPE genes were confirmed by PCR (XCR, Check-Direct CPE Screen…

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Tuesday, April 21, 2020

Genome Comparisons of Wild Isolates of Caulobacter crescentus Reveal Rates of Inversion and Horizontal Gene Transfer.

Since previous interspecies comparisons of Caulobacter genomes have revealed extensive genome rearrangements, we decided to compare the nucleotide sequences of four C. crescentus genomes, NA1000, CB1, CB2, and CB13. To accomplish this goal, we used PacBio sequencing technology to determine the nucleotide sequence of the CB1, CB2, and CB13 genomes, and obtained each genome sequence as a single contig. To correct for possible sequencing errors, each genome was sequenced twice. The only differences we observed between the two sets of independently determined sequences were random omissions of a single base in a small percentage of the homopolymer regions where a…

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Tuesday, April 21, 2020

Global-level population genomics reveals differential effects of geography and phylogeny on horizontal gene transfer in soil bacteria.

Although microorganisms are known to dominate Earth’s biospheres and drive biogeochemical cycling, little is known about the geographic distributions of microbial populations or the environmental factors that pattern those distributions. We used a global-level hierarchical sampling scheme to comprehensively characterize the evolutionary relationships and distributional limitations of the nitrogen-fixing bacterial symbionts of the crop chickpea, generating 1,027 draft whole-genome sequences at the level of bacterial populations, including 14 high-quality PacBio genomes from a phylogenetically representative subset. We find that diverse Mesorhizobium taxa perform symbiosis with chickpea and have largely overlapping global distributions. However, sampled locations cluster based on the phylogenetic…

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Tuesday, April 21, 2020

Epidemiologic and genomic insights on mcr-1-harbouring Salmonella from diarrhoeal outpatients in Shanghai, China, 2006-2016.

Colistin resistance mediated by mcr-1-harbouring plasmids is an emerging threat in Enterobacteriaceae, like Salmonella. Based on its major contribution to the diarrhoea burden, the epidemic state and threat of mcr-1-harbouring Salmonella in community-acquired infections should be estimated.This retrospective study analysed the mcr-1 gene incidence in Salmonella strains collected from a surveillance on diarrhoeal outpatients in Shanghai Municipality, China, 2006-2016. Molecular characteristics of the mcr-1-positive strains and their plasmids were determined by genome sequencing. The transfer abilities of these plasmids were measured with various conjugation strains, species, and serotypes.Among the 12,053 Salmonella isolates, 37 mcr-1-harbouring strains, in which 35 were serovar…

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Tuesday, April 21, 2020

Development of a metabolic pathway transfer and genomic integration system for the syngas-fermenting bacterium Clostridium ljungdahlii.

Clostridium spp. can synthesize valuable chemicals and fuels by utilizing diverse waste-stream substrates, including starchy biomass, lignocellulose, and industrial waste gases. However, metabolic engineering in Clostridium spp. is challenging due to the low efficiency of gene transfer and genomic integration of entire biosynthetic pathways.We have developed a reliable gene transfer and genomic integration system for the syngas-fermenting bacterium Clostridium ljungdahlii based on the conjugal transfer of donor plasmids containing large transgene cassettes (>?5 kb) followed by the inducible activation of Himar1 transposase to promote integration. We established a conjugation protocol for the efficient generation of transconjugants using the Gram-positive origins of…

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