Tag: 原子力显微镜

Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction

The emergence of multiple antibiotic-resistant bacteria, notably, pan-resistant Gram-negative pathogens, which are equipped with an outer membrane barrier of low permeability to antibiotics, has become an important challenge in recent decades following the overuse of antibiotics in humans and animals. *

In particular, the foodborne enteric pathogen Escherichia coli O157:H7 has caused severe or deadly illness cases worldwide. *

Among E. coli O157 isolates, serotype O157:H7 is the most common enteric pathogen isolated from patients with bloody diarrhea and it is also frequently found in non-bloody diarrhea samples. Many of its clinical isolates from humans and animals as well as isolates from contaminated food have been found to develop resistance to several antibiotics. *

Following the first isolation of mastoparan, the most abundant peptide in the hornet or wasp venom, from Vespula lewisii, many homologs of mastoparan were isolated from various hornets and solitary wasps. *

Mastoparan homologs are cationic tetradecapeptides with membrane permeabilizing activity and antimicrobial activity on various bacteria, mast cell degranulation activity, and hemolytic activity. *

In the article “Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction” Chun-Hsien Lin, Ching-Lin Shyu, Zong-Yen Wu, Chao-Min Wang, Shiow-Her Chiou, Jiann-Yeu Chen, Shu-Ying Tseng, Ting-Er Lin, Yi-Po Yuan, Shu-Peng Ho, Kwong-Chung Tung, Frank Chiahung Mao, Han-Jung Lee and Wu-chun Tu investigate the antimicrobial activity and membrane disruption modes of the antimicrobial peptide mastoparan-AF against hemolytic Escherichia coli O157:H7.*

Based on the physicochemical properties, mastoparan-AF may potentially adopt a 3–11 amphipathic helix-type structure, with five to seven nonpolar or hydrophobic amino acid residues forming the hydrophobic face. E. coli O157:H7 and two diarrheagenic E. coli veterinary clinical isolates, which are highly resistant to multiple antibiotics, are sensitive to mastoparan-AF, with minimum inhibitory and bactericidal concentrations (MIC and MBC) ranging from 16 to 32 μg mL−1 for E. coli O157:H7 and four to eight μg mL−1 for the latter two isolates. *

Mastoparan-AF treatment, which correlates proportionally with membrane permeabilization of the bacteria, may lead to abnormal dents, large perforations or full opening at apical ends (hollow tubes), vesicle budding, and membrane corrugation and invagination forming irregular pits or pores on E. coli O157:H7 surface. In addition, mRNAs of prepromastoparan-AF and prepromastoparan-B share a 5′-poly(A) leader sequence at the 5′-UTR known for the advantage in cap-independent translation. *

This is the first report about the physicochemical adaptation of 3–11 amphipathic helices among mastoparans or antimicrobial peptides. *

Considering that E. coli O157:H7 and clinical isolates are highly resistant to multiple classes of antibiotics, mastoparan-AF, with little or mild effect on animal RBCs, could be an effective and alternative treatment to combat hemolytic E. coli O157:H7 and other pathogenic E. coli.*

The topography of bacteria was measured by a commercial atomic force microscope using NanoWorld Pointprobe® NCSTR AFM probes with a typical resonance frequency of 160 kHz and a typical spring constant of 7.4 N/m, respectively. For image quality, the scan rates of the tip were 0.3–0.6 Hz, with a resolution set of 512 by 256 pixels, and the feedback control parameters were optimized. *

Figure 5 from «Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction» by Chun-Hsien Lin et al.:The topology of mastoparan-AF treated-hemolytic E. coli O157:H7 analyzed by AFM. (A) Two-dimensional (2D) and (B) three-dimensional (3D) images show smooth cell surfaces of untreated hemolytic E. coli O157:H7. (C) A 2D image of mastoparan-AF (32 μg mL−1)-treated hemolytic E. coli O157:H7. Abnormal perforations and dents on the surface of bacteria are indicated by arrows and arrowheads, respectively. The 3D images focusing on two highlighted areas of (C), respectively, reveal (D) a rough cell surface and (E) a hollow tube resulting from perforations at apical ends. (F) A 3D image shows a mastoparan-AF-treated bacterium with a budding vesicle. (G) A 3D image shows mastoparan-AF-treated bacteria with a wrinkled or rough surface. (H) Magnification of portion of (G) displays, in high resolution, the surface roughness of a mastoparan-AF-treated bacterium. The topography of bacteria was measured by a commercial atomic force microscope using NanoWorld Pointprobe® NCSTR AFM probes with a typical resonance frequency of 160 kHz and a typical spring constant of 7.4 N/m, respectively. For image quality, the scan rates of the tip were 0.3–0.6 Hz, with a resolution set of 512 by 256 pixels, and the feedback control parameters were optimized. *
Figure 5 from «Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction» by Chun-Hsien Lin et al.:
The topology of mastoparan-AF treated-hemolytic E. coli O157:H7 analyzed by AFM. (A) Two-dimensional (2D) and (B) three-dimensional (3D) images show smooth cell surfaces of untreated hemolytic E. coli O157:H7. (C) A 2D image of mastoparan-AF (32 μg mL−1)-treated hemolytic E. coli O157:H7. Abnormal perforations and dents on the surface of bacteria are indicated by arrows and arrowheads, respectively. The 3D images focusing on two highlighted areas of (C), respectively, reveal (D) a rough cell surface and (E) a hollow tube resulting from perforations at apical ends. (F) A 3D image shows a mastoparan-AF-treated bacterium with a budding vesicle. (G) A 3D image shows mastoparan-AF-treated bacteria with a wrinkled or rough surface. (H) Magnification of portion of (G) displays, in high resolution, the surface roughness of a mastoparan-AF-treated bacterium.

*Chun-Hsien Lin, Ching-Lin Shyu, Zong-Yen Wu, Chao-Min Wang, Shiow-Her Chiou, Jiann-Yeu Chen, Shu-Ying Tseng, Ting-Er Lin, Yi-Po Yuan, Shu-Peng Ho, Kwong-Chung Tung, Frank Chiahung Mao, Han-Jung Lee and Wu-chun Tu
Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction
Membranes 2023, 13(2), 251
DOI: https://doi.org/10.3390/membranes13020251

The article “Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3–11 Amphipathic Helices to Favor Membrane Interaction” by Chun-Hsien Lin, Ching-Lin Shyu, Zong-Yen Wu, Chao-Min Wang, Shiow-Her Chiou, Jiann-Yeu Chen, Shu-Ying Tseng, Ting-Er Lin, Yi-Po Yuan, Shu-Peng Ho, Kwong-Chung Tung, Frank Chiahung Mao, Han-Jung Lee and Wu-chun Tu is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus

Extremely robust cohesion triggered by calcium silicate hydrate (C–S–H) precipitation during cement hardening makes concrete one of the most commonly used man-made materials. *

In the article “Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus” Teresa Liberto, Andreas Nenning, Maurizio Bellotto, Maria Chiara Dalconi, Dominik Dworschak, Lukas Kalchgruber, Agathe Robisson, Markus Valtiner and Joanna Dziadkowiec present a proof-of-concept study, in which they seek an additional nanoscale understanding of early-stage cohesive forces acting between hydrating model tricalcium silicate (C3S) surfaces by combining rheological and surface force measurements. *

The composition and surface properties of the PLD-deposited calcium silicate films have been analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and atomic force microscopy (AFM). *

The calcium silicate surfaces were initially scanned in air. Subsequently, the authors injected about 1 mL of MilliQ water on top of the films so that both the sample and the AFM tip were submersed and followed the evolution of topography within the same region on a surface. The resultant images were processed in AR software by applying a 5 × 5 median filter. Roughness values were reported as root-mean-square (rms) values of the measured surface heights. *

Teresa Liberto et al. further used Atomic Force Microscopy AFM to study the nanoscale details of the film topography. The measurements performed in air revealed that the calcium silicate films are polycrystalline and are composed of uniform-sized nanograins, smaller than 100 nm in diameter (Figure 6A). At larger scan sizes, they also detected a significant amount of much larger, micron-sized particles that contribute to the quite high surface roughness; however, these were mostly located on sample edges, away from the PLD plume center.*

Subsequent AFM measurements in liquid confirmed that the films do not undergo full dissolution in water for several hours, as tested by continuously scanning the surface fully immersed in water as shown in Figure 6B. The rms roughness of the films in air was 1.2 nm (scan size 1 × 1 μm2), and it significantly increased upon exposure to H2O (rms up to 7 nm for a scan size of 1 × 1 μm2; see Figure 6C). *

The authors also detected a significant change in the film topography in water, with nanoparticles becoming less defined on a surface. This indicates that the films reprecipitated or swelled in contact with water, suggesting the gel-like character of the reprecipitated layer.*

However, despite the low thickness of the PLD-deposited films, there was no indication of complete dissolution–reprecipitation of the films: a smooth mica substrate topography that would indicate film dissolution was not exposed and a rough particle-laden surface was preserved throughout the whole measurement in water. In addition, there was no evidence of complete film dissolution in the SFA measurements; dissolution-related reduction in film thickness would have been indicated by the SFA-coupled white-light interferometric fringes. Therefore, the thin films behave as good model systems to study the early dissolution–reprecipitation phase by microscale surface force measurements. *

NanoWorld ARROW-UHFAuD AFM probes were used for the Atomic Force Microscopy.

The findings presented in the article confirm the strong cohesive properties of hydrated calcium silicate surfaces that, based on the authors’ preliminary SFA measurements, are attributed to sharp changes in the surface microstructure. In contact with water, the brittle and rough C3S surfaces with little contact area weather into soft, gel-like C–S–H nanoparticles with a much larger surface area available for forming direct contacts between interacting surfaces. *

Figure 6. Atomic force microscopy topography maps of calcium silicate films in air (A) and in water ((B) sample immersed in H2O for 30 min). The panels below AFM maps show height profiles along the center of each AFM image as marked with a dashed magenta line. Note that the y axis is the same in both panels. (C) Comparison of the root-mean-square (rms) roughness measured in air and in water (over 1.5 h in the same position) for a 1 × 1 μm2 scan size. Each point corresponds to one AFM scan, including the measurement in air. NanoWorld ARROW-UHFAuD AFM probes were used.
Figure 6 from “Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus “ by Teresa Liberto et al.:
Atomic force microscopy topography maps of calcium silicate films in air (A) and in water ((B) sample immersed in H2O for 30 min). The panels below AFM maps show height profiles along the center of each AFM image as marked with a dashed magenta line. Note that the y axis is the same in both panels. (C) Comparison of the root-mean-square (rms) roughness measured in air and in water (over 1.5 h in the same position) for a 1 × 1 μm2 scan size. Each point corresponds to one AFM scan, including the measurement in air.

*Teresa Liberto, Andreas Nenning, Maurizio Bellotto, Maria Chiara Dalconi, Dominik Dworschak, Lukas Kalchgruber, Agathe Robisson, Markus Valtiner and Joanna Dziadkowiec
Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus
Langmuir 2022, 38, 48, 14988–15000
DOI: https://doi.org/10.1021/acs.langmuir.2c02783

The article “Detecting Early-Stage Cohesion Due to Calcium Silicate Hydration with Rheology and Surface Force Apparatus” by Teresa Liberto, Andreas Nenning, Maurizio Bellotto, Maria Chiara Dalconi, Dominik Dworschak, Lukas Kalchgruber, Agathe Robisson, Markus Valtiner and Joanna Dziadkowiec is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

Over several decades many studies on the reduction of wear of mechanical systems have been conducted.
Methods to reduce wear are generally divided into the following categories: applying lubrication, coating with high-hardness materials, and surface texturing. *

Several studies have reported that coatings with higher hardness show more wear than those with lower hardness. From these reports, it is apparent that wear does not depend solely on the hardness of the surface.  Hence, there is a strong motivation for utilizing additional strategies for designing wear-resistive surfaces rather than only enhancing the hardness of the coating. *

In the article “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim show, that a soft, thin film comprising randomly aligned carbon nanotubes (CNTs) can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure. *

To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film, multi-walled CNTs (MWCNTs) and diamond-like carbon (DLC) thin films were prepared to conduct nanoscale tribological experiments using atomic force microscopy (AFM). The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load. *

To demonstrate the wear reduction mechanism of the MWCNT thin film, its indentation and frictional behaviors were assessed. The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film. The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions. *

The presented results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures. *

The thickness and surface roughness of the MWCNT and DL thin films were measured using Atomic Force Microscopy. *

The force-displacement (F-D) curves were measured on the MWCNT thin film using the AFM to verify the mechanical behavior when indented by the zirconia microspheres that were used for wear and friction experiments. *

The adhesion forces between the thin films and zirconia microspheres were measured by observing the pull-off force of the F-D curve with the AFM. *

The adhesion force was measured using a colloidal AFM probe to aid the analysis of the tribological characteristics of the thin film. *

The pull-off forces for the DL specimens were obtained at 35 different locations with displacements of 50-200 nm. *

Diamond-coated AFM probes (NanoWorld Pointprobe® DT-NCHR ) were used for scanning, while non-coated silicon AFM probes with relatively high and low spring constants (NanoWorld Pointprobe® NCHR and CONTR) were used for the tribological experiments and specimen characterizations. *

Diamond-coated AFM probes (NanoWorld Pointprobe® DT-NCHR ) were used for scanning, while non-coated silicon AFM probes with relatively high and low spring constants (NanoWorld Pointprobe® NCHR and CONTR) were used for the tribological experiments and specimen characterizations.
Figure 6 from “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” by Kuk-Jin Seo et al.:
AFM images of wear tracks on the MWCNT thin film under test conditions of (a) 2,000 nN and 20,000 cycles, (b) 6,000 nN and 30,000 cycles, (c) 7,000 nN and 30,000 cycles, (d) 9,200 nN and 30,000 cycles, (e) 13,500 nN and 30,000 cycles, and (f) 28,000 nN and 30,000 cycles. Post-processed AFM images that subtracted the original image before each wear test under conditions of (g) 6,000 nN and 30,000 cycles, (h) 7,000 nN and 30,000 cycles, and (i) 28,000 nN and 30,000 cycles

*Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim
Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief
Friction 11(7): 1292-1306 (2023)
DOI: https://doi.org/10.1007/s40544-022-0669-7

Please follow this external link to read the full article: https://rdcu.be/dejTa

The article “Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief” by Kuk-Jin Seo, Hyun-Joon Kim and Dae-Eun Kim is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.