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WIREs Nanomed Nanobiotechnol
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Effects of antibacterial agents and drugs monitored by atomic force microscopy

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Abstract Originally invented for topographic imaging, atomic force microscopy (AFM) has evolved into a multifunctional biological toolkit, enabling to measure structural and functional details of cells and molecules. Its versatility and the large scope of information it can yield make it an invaluable tool in any biologically oriented laboratory, where researchers need to perform characterizations of living samples as well as single molecules in quasi‐physiological conditions and with nanoscale resolution. In the last 20 years, AFM has revolutionized the characterization of microbial cells by allowing a better understanding of their cell wall and of the mechanism of action of drugs and by becoming itself a powerful diagnostic tool to study bacteria. Indeed, AFM is much more than a high‐resolution microscopy technique. It can reconstruct force maps that can be used to explore the nanomechanical properties of microorganisms and probe at the same time the morphological and mechanical modifications induced by external stimuli. Furthermore it can be used to map chemical species or specific receptors with nanometric resolution directly on the membranes of living organisms. In summary, AFM offers new capabilities and a more in‐depth insight in the structure and mechanics of biological specimens with an unrivaled spatial and force resolution. Its application to the study of bacteria is extremely significant since it has already delivered important information on the metabolism of these small microorganisms and, through new and exciting technical developments, will shed more light on the real‐time interaction of antimicrobial agents and bacteria. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology

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Force image of one Bordetella pertussis Vir+ cell (a), its corresponding E histogram (b), and its surface elasticity map (c). The same analysis repeated on a different B. pertussis Vir+ cell (d). (Reprinted with permission from Ref . Copyright 2012 American Chemical Society)
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Time series of topographical and stiffness variations of an Escherichia coli cell exposed to ampicillin. Panels (a), (d), and (g): 5 × 5 µm, 32 × 32 pixel topography images of a single E. coli immobilized on the substrate and imaged in PBS, PBS with ampicillin and LB. (b), (e), and (h) corresponding stiffness images evidencing that mechanical properties of the cell. (c), (f), and (i) Histograms of the stiffness values obtained from the force volume images. Two curves are evidenced: in red the membrane contribution and in black the peak of the substrate stiffness. (Reprinted with permission from Ref . Copyright 2013 Elsevier Ltd)
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Time series of the Escherichia coli cell disruption induced by CM15, imaged with high‐speed atomic force microscopy (AFM). CM15 injected at t = −6 s and images recorded every 13 s, with a resolution of 1024 × 256 pixels and a rate of 20 lines s−1. The surface of the upper bacterium (1) starts changing within 13 s. The lower bacterium (2) resists changing for 78 s. (Reprinted with permission from Ref . Copyright 2010 Nature Publishing Group)
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Atomic force microscopy (AFM) images of Escherichia coli, before and after treatment with COS (left) and chitosan (right). The top image is of untreated bacteria, and below treatment times are as indicated in the image. (Reprinted with permission from Ref . Copyright 2008 Elsevier Ltd)
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Schematics of the different operating modes of atomic force microscopy (AFM). Each mode allows characterizing different properties of the bacteria. (a) topography, (b) mechanical properties, (c) chemical mapping, and (d) mass and motion detection.
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(a) Representation of the setup of a typical nanomotion experiment: the cantilever (C) and the attached living bacteria (B). (b) Deflection of the sensor (top) and corresponding variance (bottom) for the nanomotion experiments involving Escherichia coli. The time axis indicates the minute (starting from bacterial injection at ‘B’) when each recording was started. The ‘A’ line indicates when ampicillin was injected. (Reprinted with permission from Ref . Copyright 2013 Nature Publishing Group)
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Atomic force microscopy (AFM) height (a–b) and stiffness data (c) for Rhodococcus wratislaviensis in MM medium. The stiffness histogram (d) is related to the AFM stiffness image (c). (Reprinted with permission from Ref . Copyright 2013 PLOS)
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Diagnostic Tools > Diagnostic Nanodevices
Nanotechnology Approaches to Biology > Nanoscale Systems in Biology
Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease

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