Whole genome sequencing reveals the emergence of a Pseudomonas aeruginosa shared strain sub-lineage among patients treated within a single cystic fibrosis centre

Abstract Background Chronic lung infections caused by Pseudomonas aeruginosa are a significant cause of morbidity and mortality in people with cystic fibrosis (CF). Shared P. aeruginosa strains, that can be transmitted between patients, are of concern and in Australia the AUST-02 shared strain is predominant in individuals attending CF centres in Queensland and Western Australia. M3L7 is a multidrug resistant sub-type of AUST-02 that was recently identified in a Queensland CF centre and was shown to be associated with poorer clinical outcomes. The main aim of this study was to resolve the relationship of the emergent M3L7 sub-type within the AUST-02 group of strains using whole genome sequencing. Results A whole genome core phylogeny of 63 isolates indicated that M3L7 is a monophyletic sub-lineage within the context of the broader AUST-02 group. Relatively short branch lengths connected all of the M3L7 isolates. A phylogeny based on nucleotide polymorphisms present across the genome showed that the chronological estimation of the most recent common ancestor was around 2001 (± 3 years). SNP differences between sequential non-hypermutator M3L7 isolates collected 3–4 years apart from five patients suggested both continuous infection of the same strain and cross-infection of some M3L7 variants between patients. The majority of polymorphisms that were characteristic of M3L7 (i.e. acquired after divergence from all other AUST-02 isolates sequenced) were found to produce non-synonymous mutations in virulence and antibiotic resistance genes. Conclusions M3L7 has recently diverged from a common ancestor, indicating descent from a single carrier at a CF treatment centre in Australia. Both adaptation to the lung and transmission of M3L7 between adults attending this centre may have contributed to its rapid dissemination. Further genomic investigations are required on multiple intra-sample isolates of this sub-type to decipher potential mechanisms which facilitates its epidemiological success

Dielectric Relaxation In Montmorillonite/Polymer Nanocomposites

We report dielectric relaxation behavior in blends of sodium montmorillonite particles (MM) with a series of polymers (i.e., polyisoprene (PI), poly(propylene glycol) (PPG), and poly(butylene oxide) (PBO)). These polymers are known to exhibit the dielectric normal mode due to the fluctuation of the end-to-end vector as well as the segmental mode due to local, segmental fluctuations. The data indicate that all blend systems exhibit an additional relaxation process at a temperature region below the glass transition temperature, T-g, of the pure polymer component. The intensity of the new relaxation process increases with the content of MM and hence the relaxation process can be assigned to the segmental motion of the chains intercalated in the interlayers of MM. On the other hand, the relaxation time of the normal mode reflecting the fluctuation of the end-to-end vector is the same as the neat polymers but the intensity of the relaxation process increases due to enhancement of the internal electric field by MM. (c) 2006 Elsevier Ltd. All rights reserved

Neutron Scattering Study of the Structural Change Induced by Photopolymerization of AOT/D(2)O/Dodecyl Acrylate Inverse Microemulsions

Small-angle and ultrasmall-angle neutron scattering (SANS/USANS) measurements were used to determine the structural changes induced by photopolymerization of AOT/D2O/(dodecyl acrylate) inverse microemulsion systems. Scattering profiles were collected for the initial microemulsions and the films resulting from photopolymerization of the oil phase. The SANS data for the microemulsions were modeled as spherical, core−shell droplets. Upon polymerization, the clear mircoemulsions formed opaque films. From the SANS/USANS data of the films, it was apparent that this morphology was not preserved upon polymerization; however, it was clearly observed that the formulation of the microemulsion had a large impact on the structure within the films. The Guinier region in the USANS data (2.5 × 10−5 Å−1 ≤ Q ≤ 5.3 × 10−3 Å−1) from the films indicates that very large structures are formed. Simultaneously, a well-defined peak (0.15 Å−1 ≤ Q ≤ 0.25 Å−1) in the SANS data indicates that there are also much smaller structures formed. It is proposed that the low-Q scattering arises from aggregation of the nanometer-size water droplets in the microemulsion to form droplets large enough to scatter visible light, while the peak in the high-Q region results from bilayered structures formed by the surfactant

Influence of Ionic Aggregation On the Surface Energies of Crystallites In Poly(butylene Terephthalate) Ionomers

The influence of ionic comonomer units and ionic aggregation on the crystallization behavior and crystallite surface energies of poly(butylene terephthalate-co-5-sodiosulfoisophthalate) (PBTi) ionomers containing 3 and 5 mol% dimethyl-5-sodiosulfoisophthalate monomer units is compared to that of pure poly(butylene terephthalate). The rate of crystallization of the ionomers, as determined from an Avrami analysis, was shown to decrease with an increase in the ionic comonomer unit content. This behavior was attributed to the presence of non-crystallizable comonomer units and the reduced mobility of the crystallizable chain segments due to ionic aggregation in the PBT ionomers as evidenced by the broad peak centered about -9.5 ppm in the Na-23 NMR spectrum. The surface free energies of the polymer crystallites were determined using the Avrami rate constants in a modified Laurizten-Hoffman method. The PBT ionomers showed a 35-70% increase in the product of the surface energies (sigmasigma(e)) over that observed for pure PBT. By assuming a constant lateral surface energy, this behavior was attributed to a 30-70% increase in the work associated with chain folding. Relative to crystallites formed in pure PBT, these data suggest that there is a more disordered crystalline fold surface in the ionomers due the perturbed development of crystallites in the presence of a strong electrostatic network. (C) 2004 Elsevier Ltd. All fights reserved

Variable Temperature F-19 Solid-State NMR Study of the Effect of Electrostatic Interactions On Thermally-Stimulated Molecular Motions In Perfluorosulfonate lonomers

This study uses variable temperature F-19 solid-state nuclear magnetic resonance (SSNMR) spectroscopy to determine the influence of electrostatic interactions on the T-1, T-1 rho, and T-2 values of Nafion (R). Because of a homogenizing of the T-1\u27s as a result of spin diffusion, it was not possible to resolve from the T, experiments the relative motions of the side- and main-chain. The initial increase in T-1 rho, as a function of increasing temperature has been attributed to backbone rotations that increase with increasing temperature. The maxima observed in the T-1 rho, plots suggest a change in the dominant relaxation mechanism at that temperature. The similarity in relaxation behavior of the side- and main-chains suggests that the motions are dynamically coupled, because of the fact that the side-chain is directly attached to the main-chain. Two T-1 rho, values were observed for the main-chain at high temperatures, which has been attributed to a thermally activated ion-hopping process. The results of T2 studies show that correlated motions of the side- and main-chain exist at low temperatures. However, at elevated temperatures the T-2 values for the side-chain increase rapidly while remaining relatively constant for the main-chain, indicating an onset of mobility of the side-chains. (c) 2007 Wiley Periodicals, Inc

Molecular Origins of the Thermal Transitions and Dynamic Mechanical Relaxations In Perfluorosulfonate Ionomers

The study presented here is a fundamental investigation into the molecular origins of the thermal transitions and dynamic mechanical relaxations of Nafion membranes as studied by DSC, DMA, variable temperature small-angle X-ray scattering (SAXS), and solid-state F-19 NMR spectroscopy. While several studies in the literature have attempted to explain the molecular origins of these thermal transitions and mechanical relaxations, the assignments were based primarily on limited DMA results and have at times been contradictory. In DSC traces of Nafion, the low- and high-temperature endotherms are shown to be dependent on thermal history and are now attributed to melting of relatively small and large crystallites, respectively. DSC analysis of Nafion yields information only on the crystalline nature of this ionomer, and neither of the transitions can be assigned to glass transitions. The intensity of the small-angle ionomer peak at ca. q = 2 nm(-1) was monitored as a function of temperature for each alkylammonium neutralized sample. Changes in intensity of the ionomer peak as a function of temperature were shown to correlate well with the a and P relaxations observed in DMA. Variable temperature solid-state F-19 NMR techniques were used to investigate the dynamics of the Nafion chains. Spin-diffusion experiments revealed a profound increase in mobility at the onset of the a relaxation. Sideband analysis indicated that the side chain is more mobile than the main chain and that the mobility is greatly affected by the size of the counterion. Molecular level information from this analysis in correlation with SAXS and DMA data supports the assignment of the beta relaxation to the genuine T-g of Nafion and the alpha relaxation to the onset of long-range mobility of chains/side chains via a thermally activated destabilization of the electrostatic network

Counterion Dependent Crystallization Kinetics in Blends of a Perfluorosulfonate Ionomer With Poly(vinylidene Fluoride)

Blends of poly(vinylidene fluoride) (PVDF) with a perfluorosulfonate ionomer, Nafion (R), have been prepared and examined in terms of the crystallization kinetics of the PVDF component. In blends of PVDF with Na+-form Nafion (R), the rates of bulk crystallization, as observed by DSC, and the spherulitic growth rates of the PVDF component, as observed using optical microscopy, were found to be very similar to that of pure PVDF. This behavior was attributed to the course phase separation of Na+-form Nafion (R) from PVDF and melt incompatibility of the physically cross-linked ionomer with the crystallizable component. In this segregated state, the PVDF component of the blend is allowed to crystallize in pure phases that are isolated under the influence of Nafion (R). In contrast, when the ionomer was exchanged with more weakly interacting quaternary alkylammonium counterions, a decrease in both the rate of bulk crystallization and spherulitic growth was observed. Furthermore, the crystallization kinetics of PVDF in these blends was found to be dependent on the counterion size; as the size of counterions associated with the Nafion component increased, the rate of crystallization decreased. This behavior was attributed to a weakening of the electrostatic interactions in the ionomer phase and thus an increase in the extent of phase mixing with the larger ions. (c) 2006 Elsevier Ltd. All rights reserved