Gram-negative bacteria have an outer membrane inhibiting the entry of antibiotics. Porins, found within the outer membrane, are involved in regulating the permeability of β-lactam antibiotics. ...β-lactamases are enzymes that are able to inactivate the antibacterial properties of β-lactam antibiotics. Interestingly, porins and β-lactamase are found in outer membrane vesicles (OMVs) of β-lactam-resistant
and may be involved in the survival of susceptible strains of
in the presence of antibiotics, through the hydrolysis of the β-lactam antibiotic. In this study, OMVs isolated from β-lactam-resistant
and from mutants, lacking porin or β-lactamase, were evaluated to establish if the porins or β-lactamase in OMVs were involved in the degradation of β-lactam antibiotics. OMVs isolated from
deficient in β-lactamase did not show any degradation ability against β-lactam antibiotics, while OMVs lacking OmpC or OmpF showed significantly lower levels of hydrolyzing activity than OMVs from parent
. These data reveal an important role of OMVs in bacterial defense mechanisms demonstrating that the OmpC and OmpF proteins allow permeation of β-lactam antibiotics into the lumen of OMVs, and antibiotics that enter the OMVs can be degraded by β-lactamase.
This study investigated the recovery stress and bond resistance of cold drawn crimped SMA fiber using two different initial diameters of 1.0 and 0.7 mm. These characteristics are important to the ...active prestressing effect and crack-closing of the fiber. NiTi SMA fiber was used for the cold drawing, and then crimped shapes were manufactured with various wave heights. After that, tensile, recovery, and pullout tests were conducted. The cold drawn crimped fiber showed softening tensile behavior more clearly than the cold drawn straight fiber when not subjected to heating, whereas they had the same tensile behavior under heating. The recovery stress and the residual stress of the crimped fibers were less than those of the straight fiber with the same diameter. Moreover, crimped fibers with a large diameter and higher wave height would induce more recovery stress and residual stress. The maximum pullout resistance of the crimped fiber was a function of the wave depth, embedded length, yield strength, and flexural rigidity of the fiber.
A series of Zn–porphyrin dyes was prepared and anchored onto a TiO2 surface to complete a dye-sensitized photocatalyst system, Zn–porphyrin-|TiO2|-Cat, and tested as lower energy photosensitizers for ...photocatalytic CO2 reduction. Three major synthetic modifications were performed on the Zn–porphyrin dye to obtain a lower energy sensitization and improve the catalyst lifetime. We found that incorporating acetylene and linear hexyl groups into the Zn–porphyrin core allowed facile lower energy sensitization, and the addition of the cyanophosphonic acid as an anchoring group gave the long-term dye stability on the TiO2 surface. Under irradiation with red light of >550 nm and a light intensity of 207 mW/cm2, the hybrid ZnP CNPA catalyst showed a TONRe of ∼800 over an extended time period of 90 h. The photocatalytic activities of porphyrin hybrids differ greatly with the binding strength of the anchoring groups of dye and spectral range of the irradiated light and its intensity.
Extracellular vesicles (EVs) containing specific cargo molecules from the cell of origin are naturally secreted from bacteria. EVs play significant roles in protecting the bacterium, which can ...contribute to their survival in the presence of antibiotics. Herein, we isolated EVs from methicillin-resistant Staphylococcus aureus (MRSA) in an environment with or without stressor by adding ampicillin at a lower concentration than the minimum inhibitory concentration (MIC). We investigated whether EVs from MRSA under stress condition or normal condition could defend susceptible bacteria in the presence of several β-lactam antibiotics, and directly degrade the antibiotics. A comparative proteomic approach was carried out in both types of EVs to investigate β-lactam resistant determinants. The secretion of EVs from MRSA under antibiotic stressed conditions was increased by 22.4-fold compared with that of EVs without stress. Proteins related to the degradation of β-lactam antibiotics were abundant in EVs released from the stressed condition. Taken together, the present data reveal that EVs from MRSA play a crucial role in the survival of β-lactam susceptible bacteria by acting as the first line of defense against β-lactam antibiotics, and antibiotic stress leads to release EVs with high defense activity.
Avian pathogenic Escherichia coli (APEC) causes extensive mortality in poultry flocks, leading to extensive economic losses. The aim of this study was to investigate the phenotypic and genotypic ...characteristics and antimicrobial resistance of recent APEC isolates. Of the 79 APEC isolates, the most predominant serogroup was O78 (16 isolates, 20.3%), followed by O2 (7 isolates, 8.9%) and O53 (7 isolates, 8.9%). Thirty-seven (46.8%) and six (7.6%) of the isolates belonged to phylogenetic groups D and B2, respectively, and presented as virulent extraintestinal E. coli. Among 5 analyzed virulence genes, the highest frequency was observed in hlyF (74 isolates, 93.7%), followed by iutA (72 isolates, 91.9%) gene. The distribution of the iss gene was significantly different between groups A/B1 and B2/D (P < 0.05). All group B2 isolates carried all 5 virulence genes. APEC isolates showed high resistance to ampicillin (83.5%), nalidixic acid (65.8%), tetracycline (64.6%), cephalothin (46.8%), and ciprofloxacin (46.8%). The β-lactamases–encoding genes blaTEM-1 (23 isolates, 29.1%), blaCTX-M-1 (4 isolates, 5.1%), and blaCTX-M-15 (3 isolates, 3.8%); the aminoglycoside-modifying enzyme gene aac(3)-II (4 isolates, 5.1%); and the plasmid-mediated quinolone genes qnrA (10 isolates, 12.7%) and qnrS (2 isolates, 2.5%) were identified in APEC isolates. The tetA (37 isolates, 46.8%) and sul2 (20 isolates, 25.3%) were the most prevalent among tetracycline and sulfonamide resistant isolates, respectively. This study indicates that APEC isolates harbor a variety of virulence and resistance genes; such genes are often associated with plasmids that facilitate their transmission between bacteria and should be continuously monitored to track APEC transmission in poultry farms.
Polycyclic aromatic hydrocarbons (PAHs) are known to be representative carcinogenic environmental pollutants with high toxicity. However, information on the potential ecological and environmental ...risks of PAH contamination in soil remains scarce. Thus, this study was evaluated the potential ecological risks of PAHs in soils of five Korean areas (Gunsan (GS), Gwangju, Yeongnam, Busan, and Gangwon) using organic carbon (OC)-normalized analysis, mean effect range-median quotient (M-ERM-Q), toxic equivalent quantity (TEQ) analysis, and risk quotient (RQ) derived by the species sensitivity distribution model. In this study, atmospheric particulate matter has a significant effect on soil pollution in GS through the presence of hopanes and the similar pattern of PAHs in soil and atmospheric PAHs. From analysis of source identification, combustion sources in soils of GS were important PAH sources. For PAHs in soils of GS, the OC-normalized analysis, M-ERM-Q, and TEQ analysis have 26.78 × 105 ng/g-OC, 0.218, and 49.72, respectively. Therefore, the potential ecological risk assessment results showed that GS had moderate–high ecological risk and moderate–high carcinogenic risk, whereas the other regions had low ecological risk and low–moderate carcinogenic risk. The risk level (M-ERM-Q) of PAH contamination in GS was similar to that in Changchun and Xiangxi Bay in China. The Port Harcourt City in Nigeria for PAH has the highest risk (M-ERM-Q = 4.02 and TEQ = 7923). Especially, compared to China (RQPhe =0.025 and 0.05), and Nigeria (0.059), phenanthrene showed the highest ecological risk in Korea (0.001–0.18). Korea should focus on controlling the release of PAHs originating from the PM in GS.
•Atmospheric particulate matter (PM) significantly affected soil pollution in GS.•PM-contaminated soils were tested to assess the potential ecological risk of PAHs.•Combustion sources are important sources of PAHs in the GS soils.•PAH pollution level in GS was classified as moderate-high risk.•PAHs in GS must be controlled to reduce the effects of PAHs on the environment.
The chopping frequency of the modulated light is one of the involved parameters in photoreflectance spectroscopy. To achieve more accurate photoreflectance spectra, we need to give enough time to the ...signal to reach its minimum/maximum values, for which the characteristic time constant of the signal is known as a criterion. In this work, with the help of the concept of the time constant of the photoreflectance signal, limitations were found for the chopping frequency. Photoreflectance spectroscopy of
p
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n
and
p
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i
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n
GaAs junctions was investigated, and the measurements were based on low excitation intensities and the exponential form of the photoreflectance signal. Instead of the method that relies on in-phase and out-phase amplitudes variations, the characteristic time constants were calculated by analyzing the phase diagram of the spectrum. The measurements were done for different excitation wavelengths, including 405, 520, and 637 nm, and the results show other limits on chopping frequencies for different excitation wavelengths. Finally, the effect of high chopping frequency on the critical parameters (electric field and lifetime broadening parameter) was investigated.
•Two nonlinear analytical models of RC columns are developed in OPENSEES.•Experimental results of RC columns retrofitted by FRP wire jackets are used.•Two models are compared from a practical point ...of view.•Seismic fragility curves of RC columns are generated using the two models.
This study assessed the seismic vulnerability of reinforced concrete columns jacketed by fiber-reinforced polymer (FRP) wires. To achieve this goal, four column specimens subjected to cyclic load tests were selected to validate the analytical model of existing and FRP retrofitted columns in OpenSees; the specimens included two existing columns with lap-spliced and continuous longitudinal reinforcement and two FRP wire-jacketed columns with lap-spliced and continuous longitudinal reinforcement. Two types of material models (‘Concrete’ versus ‘Pinching’) were used to simulate the concrete material models of columns. Based on the validation results, the advantages and disadvantages of using of two material models were considered. Additionally, to compare the seismic performance of the columns subjected to ground motions, their fragility curves were developed. Comparison results revealed that the retrofitting effect using the ‘Pinching’ model is superior, but use of the ‘Concrete’ model is also acceptable. However, the ‘Pinching’ model is more vulnerable than the ‘Concrete’ model for specimens exhibiting limited ductility.
Methamphetamine (METH) is a powerful psychostimulant that is causing serious health problems worldwide owing to imprudent abuses. Recent studies have suggested that METH has deleterious effects on ...the blood–brain barrier (BBB). A few studies have also been conducted on the mechanisms whereby METH-induced oxidative stress causes BBB dysfunction. We investigated whether
N
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tert
-butyl-α-phenylnitrone (PBN) has protective effects on BBB function against METH exposure in primary human brain microvascular endothelial cells (HBMECs). We found that METH significantly increased reactive oxygen species (ROS) generation in HBMECs. Pretreatment with PBN decreased METH-induced ROS production. With regard to BBB functional integrity, METH exposure elevated the paracellular permeability and reduced the monolayer integrity; PBN treatment reversed these effects. An analysis of the BBB structural properties, by immunostaining junction proteins and cytoskeleton in HBMECs, indicated that METH treatment changed the cellular localization of the tight (ZO-1) and adherens junctions (VE-cadherin) from the membrane to cytoplasm. Furthermore, METH induced cytoskeletal reorganization
via
the formation of robust stress fibers. METH-induced junctional protein redistribution and cytoskeletal reorganization were attenuated by PBN treatment. Our results suggest that PBN can act as a therapeutic reagent for METH-induced BBB dysfunction by inhibiting excess ROS generation.
Linezolid is an oxazolidinone class antibiotic used for treatment infections caused by various multidrug-resistant gram-positive pathogens including enterococci. However, recently, ...linezolid-resistant isolates in animals are considered as a human health hazard. In a broiler operation system, antimicrobial resistance can be transferred to the environment and commercial broiler via the fecal–oral route. Therefore, this study was conducted to investigate the prevalence and characteristics of linezolid-resistant Enterococcus faecalis (E. faecalis) from broiler parent stock in a broiler operation system. Among 297 E. faecalis isolates from 85 flocks in 8 broiler breeder farms, the prevalence of chloramphenicol- and linezolid-resistant isolates was 0 to 12.1% and 0 to 8.0%, respectively; however, there were no significant differences between farms. Therefore, a total of 14 (4.7%) chloramphenicol- and/or linezolid-resistant E. faecalis showed resistance to 7 or more antimicrobial classes. The drug-resistance gene optrA, which can confer resistance to linezolid, tedizolid, and phenicols, was found in 8 (2.69%) isolates, and 7 (2.36%) of the 8 optrA-positive isolates co-carried the phenicol exporter gene fexA. However, E. faecalis isolates from 3 of 8 broiler breeder farms only carried the optrA and/or fexA genes. As linezolid is one of the last antimicrobial treatments of choice for multidrug-resistant gram-positive pathogens including E. faecalis, the presence of antibiotic-resistant E. faecalis in broiler breeder farms should be monitored to prevent the introduction of linezolid-resistant strains to the food chain.
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