Biofilm represents a way of life that allows greater survival of microorganisms in hostile habitats. Campylobacter jejuni is able to form biofilms in vitro and on surfaces at several points in the poultry production chain. Genetic determinants related to their formation are expressed differently between strains and external conditions are decisive in this respect. Our approach combines phylogenetic analysis and the presence of seven specific genes linked to biofilm formation in association with traditional microbiology techniques, using Mueller Hinton and chicken juice as substrates in order to quantify, classify, determine the composition and morphology of the biomass of simple and mixed biofilms of 30 C. jejuni strains. It also evaluates the inhibition of its formation by biocides commonly used in industry and also by zinc oxide nanoparticles. Genetic analysis showed high heterogeneity with the identification of 23 pulsotypes. Despite the diversity, the presence of flaA, cadF, luxS, dnaJ, htrA, cbrA, and sodB genes in all strains shows the high potential for biofilm formation. This ability was only expressed in chicken juice, where they presented phenotype of a strong biofilm producer, with a mean count of 7.37 log CFU/mL and an ultrastructure characteristic of mature biofilm. The composition of simple and mixed biofilms was predominantly composed by proteins. The exceptions were found in mixed biofilms with Pseudomonas aeruginosa, which includes a carbohydrate-rich matrix, lower ability to sessile form in chicken juice and compact architecture of the biofilm, this aspects are intrinsic to this species. Hypochlorite, chlorhexidine, and peracetic acid were more effective in controlling viable cells of C. jejuni in biofilm, but the existence of tolerant strains indicates exposure to sublethal concentrations and development of adaptation mechanisms. This study shows that in chicken juice C. jejuni presents greater potential in producing mature biofilms.
We investigated the thermal and photothermal properties of an amorphous GaSe9 alloy produced by mechanical alloying considering the photoacoustic spectroscopy and differential scanning calorimetry (DSC) techniques. The room temperature thermal diffusivity of GaSe9 was determined using the open photoacoustic cell configuration considering the thermal diffusion and thermoelastic bending effects. The glass transition and crystallization processes were investigated through DSC measurements obtained at five heating rates, and glass transition, crystallization temperatures, and activation energies were determined. The crystallization mechanism was also determined.
The pressure‐induced phase transitions in nanostructured SnSe were investigated using angle‐dispersive X‐ray diffraction in a synchrotron source along with first‐principles density functional theory (DFT) calculations. The variation of the cell parameters along with enthalpy calculations for pressures up to 18 GPa have been considered. Both the experimental and the theoretical approaches demonstrate a phase transition at around 4 GPa. Below 8.2 GPa the X‐ray diffraction patterns were fitted using the Rietveld method with space group Pnma (No. 62). The lattice parameters and atomic positions for the above‐mentioned symmetry were used in DFT calculations of thermodynamic parameters. The enthalpy calculations with the computationally optimized structure and the proposed Pnma structure of SnSe were compatible. The variations of the cell volume for the high‐pressure phases are described by a third‐order Birch–Murnaghan equation of state.
The eletronic and optical properties of amorphous GaSe thin films produced by vacuum evaporation were investigated using X-ray photoemission spectroscopy (XPS) and transmittance spectroscopy techniques. XPS measurements allowed the determination of the valence band energy and showed the chemical bonding and the charge transfer between Se and Ga atoms. Transmittance measurements allowed the determination of the optical gap, refractive index and extinction coefficient in the low and high absorption regions. Using the Wemple and DiDomenico single oscillator model we also found the oscillator and the dispersive energies. From the valence band and optical gap energies, the conduction band was found and an energy level diagram for f-GaSe is proposed.
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