The Discovery of the Role of Outer Membrane Vesicles against Bacteria.

Gram-negative bacteria are intrinsically resistant to many commercialized antibiotics. The outer membrane (OM) of Gram-negative bacteria prevents the entry of such antibiotics. Outer membrane vesicles (OMV) are naturally released from the OM of Gram-negative bacteria for a range of purposes, including competition with other bacteria.

Detection of Aminoglycoside Resistant Bacteria in Sludge Samples From Norwegian Drinking Water Treatment Plants.

Through a culture-based approach using sludge from drinking water treatment plants, this study reports on the presence of aminoglycoside resistant bacteria at 23 different geographical locations in Norway. Sludge samples are derived from a large environmental area including drinking water sources and their surrounding catchment areas. Aminoglycoside resistant bacteria were detected at 18 of the sample sites.

Vesicle-Mediated Gene Transfer in Acinetobacter baumannii.

The role of vesicle-mediated gene transfer in Acinetobacter baumannii populations has been investigated in the last decade. Importantly, outer membrane vesicles (OMVs) secreted from A. baumannii cells have proven to be efficient agents of transfer of antimicrobial resistance genes to other bacterial species.

Competence for Natural Transformation Is Common among Clinical Strains of Resistant spp.

Horizontal gene transfer events provide the basis for extensive dissemination of antimicrobial resistance traits between bacterial populations. Conjugation is considered to be the most frequent mechanism behind new resistance acquisitions in clinical pathogens but does not fully explain the resistance patterns seen in some bacterial genera. Gene transfer by natural transformation has been described for numerous clinical isolates, including some species.

Critical knowledge gaps and research needs related to the environmental dimensions of antibiotic resistance.

There is growing understanding that the environment plays an important role both in the transmission of antibiotic resistant pathogens and in their evolution. Accordingly, researchers and stakeholders world-wide seek to further explore the mechanisms and drivers involved, quantify risks and identify suitable interventions. There is a clear value in establishing research needs and coordinating efforts within and across nations in order to best tackle this global challenge.

Membrane vesicles and horizontal gene transfer in prokaryotes.

Membrane vesicles (MVs) are released from all living cells. MVs are lumen-containing spheres of lipid-bilayers derived from the cell surface. MVs are biologically active and contain various components, including genetic material.

Substitutions of short heterologous DNA segments of intragenomic or extragenomic origins produce clustered genomic polymorphisms.

In a screen for unexplained mutation events we identified a previously unrecognized mechanism generating clustered DNA polymorphisms such as microindels and cumulative SNPs. The mechanism, short-patch double illegitimate recombination (SPDIR), facilitates short single-stranded DNA molecules to invade and replace genomic DNA through two joint illegitimate recombination events. SPDIR is controlled by key components of the cellular genome maintenance machinery in the gram-negative bacterium Acinetobacter baylyi.

Distribution of class 1 integrons in a highly impacted catchment.

Polluted compounds into freshwater sediments may select and enrich bacteria carrying specific genetic compositions. Here we examine the possible use of class 1 integrons as bioindicators in freshwater environments. Samples were collected from various sediments in an urban area (Zhangye, Gansu province, China), specifically within the city, in the industrial zone, in the surrounding agricultural area and in a nearby national park.

Antibiotic resistance marker genes as environmental pollutants in GMO-pristine agricultural soils in Austria.

Antibiotic resistance genes may be considered as environmental pollutants if anthropogenic emission and manipulations increase their prevalence above usually occurring background levels. The prevalence of aph(3')-IIa/nptII and aph(3')-IIIa/nptIII - frequent marker genes in plant biotechnology conferring resistance to certain aminoglycosides - was determined in Austrian soils from 100 maize and potato fields not yet exposed to but eligible for GMO crop cultivation. Total soil DNA extracts were analysed by nptII/nptIII-specific TaqMan real time PCR.

Involvement of aph(3')-IIa in the formation of mosaic aminoglycoside resistance genes in natural environments.

Intragenic recombination leading to mosaic gene formation is known to alter resistance profiles for particular genes and bacterial species. Few studies have examined to what extent aminoglycoside resistance genes undergo intragenic recombination. We screened the GenBank database for mosaic gene formation in homologs of the aph(3')-IIa (nptII) gene.

Global dissemination patterns of common gene cassette arrays in class 1 integrons.

Integrons are genetic elements that contain a site-specific recombination system able to capture, express and exchange gene cassettes. Mobile integrons are widespread and often confer resistance to multiple antibiotics, due to the expression of the arrays of gene cassettes they carry. Although >300 cassette arrays have been described, < 10 array compositions prevail in the reports related to class 1 integrons.

Growth phase-specific evolutionary benefits of natural transformation in Acinetobacter baylyi.

Natural transformation in bacteria facilitates the uptake and genomic integration of exogenous DNA. This allows horizontal exchange of adaptive traits not easily achieved by point mutations, and has a major role in the acquisition of adaptive traits exemplified by antibiotic resistance determinants and vaccination escape. Mechanisms of DNA uptake and genomic integration are well described for several naturally transformable bacterial species; however, the selective forces responsible for its evolution and maintenance are still controversial.

Gene transfer potential of outer membrane vesicles of Acinetobacter baylyi and effects of stress on vesiculation.

Outer membrane vesicles (OMVs) are continually released from a range of bacterial species. Numerous functions of OMVs, including the facilitation of horizontal gene transfer (HGT) processes, have been proposed. In this study, we investigated whether OMVs contribute to the transfer of plasmids between bacterial cells and species using Gram-negative Acinetobacter baylyi as a model system.

Detecting rare gene transfer events in bacterial populations.

Horizontal gene transfer (HGT) enables bacteria to access, share, and recombine genetic variation, resulting in genetic diversity that cannot be obtained through mutational processes alone. In most cases, the observation of evolutionary successful HGT events relies on the outcome of initially rare events that lead to novel functions in the new host, and that exhibit a positive effect on host fitness. Conversely, the large majority of HGT events occurring in bacterial populations will go undetected due to lack of replication success of transformants.

Bacterial natural transformation by highly fragmented and damaged DNA.

DNA molecules are continuously released through decomposition of organic matter and are ubiquitous in most environments. Such DNA becomes fragmented and damaged (often <100 bp) and may persist in the environment for more than half a million years. Fragmented DNA is recognized as nutrient source for microbes, but not as potential substrate for bacterial evolution.

Prevalence of the aminoglycoside phosphotransferase genes aph(3')-IIIa and aph(3')-IIa in Escherichia coli, Enterococcus faecalis, Enterococcus faecium, Pseudomonas aeruginosa, Salmonella enterica subsp. enterica and Staphylococcus aureus isolates in Austria.

The aminoglycoside phosphotransferase aph(3')-IIa primarily inactivates kanamycin and neomycin, whilst aph(3')-IIIa also inactivates amikacin. The aim of this study was to determine the frequency of both resistance genes in major human pathogens to obtain their baseline prevalence in the gene pool of these bacterial populations in Austria. In total, 10 541 Escherichia coli, Enterococcus faecalis, Enterococcus faecium, Pseudomonas aeruginosa, Salmonella enterica subsp.

Fitness costs of various mobile genetic elements in Enterococcus faecium and Enterococcus faecalis.

Objectives: To determine the fitness effects of various mobile genetic elements (MGEs) in Enterococcus faecium and Enterococcus faecalis when newly acquired. We also tested the hypothesis that the biological cost of vancomycin resistance plasmids could be mitigated during continuous growth in the laboratory.

Methods: Different MGEs, including two conjugative transposons (CTns) of the Tn916 family (18 and 33 kb), a pathogenicity island (PAI) of 200 kb and vancomycin-resistance (vanA) plasmids (80-200 kb) of various origins and classes, were transferred into common ancestral E.

Identical miniature inverted repeat transposable elements flank class 1 integrons in clinical isolates of Acinetobacter spp.

Miniature inverted repeat transposable elements (MITEs) have been identified flanking class 1 integrons. We have identified and characterized a 439-bp MITE-like structure in seven Acinetobacter species isolates from Portugal and Brazil. The complete sequence similarity of the elements and flanking regions suggests that MITEs may act as mobilizable vectors for the dissemination of integrons.

Integrons: Vehicles and pathways for horizontal dissemination in bacteria.

Integrons are genetic elements first described at the end of the 1980s. Although most integrons were initially described in human clinical isolates, they have now been identified in many non-clinical environments, such as water and soil. Integrons are present in ≈10% of the sequenced bacterial genomes and are frequently linked to mobile genetic elements (MGEs); particularly the class 1 integrons.

Various pathways leading to the acquisition of antibiotic resistance by natural transformation.

Natural transformation can lead to exchange of DNA between taxonomically diverse bacteria. In the case of chromosomal DNA, homology-based recombination with the recipient genome is usually necessary for heritable stability. In our recent study, we have shown that natural transformation can promote the transfer of transposons, IS elements, and integrons and gene cassettes, largely independent of the genetic relationship between the donor and recipient bacteria.

Biosafety data as confidential business information.

Removal of confidentiality claims on biosafety data is necessary to adhere to standard scientific procedures of quality assurance, to increase transparency, to minimize impacts of conflicts of interests, and ultimately to improve public confidence in GMOs.

Controlling antimicrobial resistance through targeted, vaccine-induced replacement of strains.

Vaccination has proven effective in controlling many infectious diseases. However, differential effectiveness with regard to pathogen genotype is a frequent reason for failures in vaccine development. Often, insufficient immune response is induced to prevent infection by the diversity of existing serotypes present in pathogenic populations of bacteria.

A trade-off between the fitness cost of functional integrases and long-term stability of integrons.

Horizontal gene transfer (HGT) plays a major role in bacterial microevolution as evident from the rapid emergence and spread of antimicrobial drug resistance. Few studies have however addressed the population dynamics of newly imported genetic elements after HGT. Here, we show that newly acquired class-1 integrons from Salmonella enterica serovar Typhimurium and Acinetobacter baumannii, free of associated transposable elements, strongly reduce host fitness in Acinetobacter baylyi.