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1.
Sci Rep ; 14(1): 1762, 2024 01 19.
Article in English | MEDLINE | ID: mdl-38243067

ABSTRACT

The development of new antibiotics has stalled, and novel strategies are needed as we enter the age of antibiotic resistance. Certain naturally occurring clays have been shown to be effective in killing antibiotic resistant bacteria. However, these natural clays are too variable to be used in clinical settings. Our study shows that synthetic antibacterial minerals exhibit potent antibacterial activity against topical MRSA infections and increase the rate of wound closure relative to controls. The antibacterial minerals maintain a redox cycle between Fe2+/Fe3+ and the surfaces of pyrite minerals, which act as a semiconductor and produce reactive oxygen species (ROS), while smectite minerals act as a cation exchange reservoir. Acidic conditions are maintained throughout the application of the hydrated minerals and can mitigate the alkaline pH conditions observed in chronic non-healing wounds. These results provide evidence for the strategy of 'iron overload' to combat antibiotic resistant infections through the maintained release of Fe2+ and generation of ROS via distinct geochemical reactions that can break the chronic wound damage cycle.


Subject(s)
Methicillin-Resistant Staphylococcus aureus , Mice , Animals , Clay , Reactive Oxygen Species/pharmacology , Minerals/pharmacology , Anti-Bacterial Agents/pharmacology
2.
Sci Rep ; 13(1): 21256, 2023 Dec 01.
Article in English | MEDLINE | ID: mdl-38040754

ABSTRACT

Understanding the thermal decomposition behavior of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is a major focus in energetic materials research because of safety issues. Previous research and modelling efforts have suggested benzo-monofurazan condensation producing H2O is the initiating decomposition step. However, early evolving CO2 (m/z 44) along with H2O (m/z 18) evolution have been observed by mass spectrometric monitoring of head-space gases in both constant heating rate and isothermal decomposition studies. The source of the CO2 has not been explained, until now. With the recent successful synthesis of 13C6-TATB (13C incorporated into the benzene ring), the same experiments have been used to show the source of the CO2 is the early breakdown of the TATB ring, not adventitious C from impurities and/or adsorbed CO2. A shift in mass m/z 44 (CO2) to m/z 45 is observed throughout the decomposition process indicating the isotopically labeled 13C ring breakdown occurs at the onset of thermal decomposition along with furazan formation. Partially labeled (N18O2)3-TATB confirms at least some of the oxygen comes from the nitro-groups. This finding has a significant bearing on decomposition computational models for prediction of energy release and deflagration to detonation transitions, with respect to conditions which currently do not recognize this oxidation step.

3.
Appl Opt ; 61(9): F47-F54, 2022 Mar 20.
Article in English | MEDLINE | ID: mdl-35333225

ABSTRACT

Soil is a scattering medium that inhibits imaging of plant-microbial-mineral interactions that are essential to plant health and soil carbon sequestration. However, optical imaging in the complex medium of soil has been stymied by the seemingly intractable problems of scattering and contrast. Here, we develop a wavefront shaping method based on adaptive stochastic parallel gradient descent optimization with a Hadamard basis to focus light through soil mineral samples. Our approach allows a sparse representation of the wavefront with reduced dimensionality for the optimization. We further divide the used Hadamard basis set into subsets and optimize a certain subset at once. Simulation and experimental optimization results demonstrate our method has an approximately seven times higher convergence rate and overall better performance compared to that with optimizing all pixels at once. The proposed method can benefit other high-dimensional optimization problems in adaptive optics and wavefront shaping.


Subject(s)
Optics and Photonics , Soil , Computer Simulation , Optical Imaging
4.
Environ Sci Technol ; 56(3): 1994-2008, 2022 02 01.
Article in English | MEDLINE | ID: mdl-35029104

ABSTRACT

Imaging biogeochemical interactions in complex microbial systems─such as those at the soil-root interface─is crucial to studies of climate, agriculture, and environmental health but complicated by the three-dimensional (3D) juxtaposition of materials with a wide range of optical properties. We developed a label-free multiphoton nonlinear imaging approach to provide contrast and chemical information for soil microorganisms in roots and minerals with epi-illumination by simultaneously imaging two-photon excitation fluorescence (TPEF), coherent anti-Stokes Raman scattering (CARS), second-harmonic generation (SHG), and sum-frequency mixing (SFM). We used fluorescence lifetime imaging (FLIM) and time gating to correct CARS for the autofluorescence background native to soil particles and fungal hyphae (TG-CARS) using time-correlated single-photon counting (TCSPC). We combined TPEF, TG-CARS, and FLIM to maximize image contrast for live fungi and bacteria in roots and soil matrices without fluorescence labeling. Using this instrument, we imaged symbiotic arbuscular mycorrhizal fungi (AMF) structures within unstained plant roots in 3D to 60 µm depth. High-quality imaging was possible at up to 30 µm depth in a clay particle matrix and at 15 µm in complex soil preparation. TG-CARS allowed us to identify previously unknown lipid droplets in the symbiotic fungus, Serendipita bescii. We also visualized unstained putative bacteria associated with the roots of Brachypodium distachyon in a soil microcosm. Our results show that this multimodal approach holds significant promise for rhizosphere and soil science research.


Subject(s)
Mycorrhizae , Soil , Minerals , Rhizosphere , Spectrum Analysis, Raman/methods
5.
Sci Rep ; 12(1): 1218, 2022 01 24.
Article in English | MEDLINE | ID: mdl-35075234

ABSTRACT

The overuse of antibiotics in clinical and livestock settings is accelerating the selection of multidrug resistant bacterial pathogens. Antibiotic resistant bacteria result in increased mortality and financial strain on the health care and livestock industry. The development of new antibiotics has stalled, and novel strategies are needed as we enter the age of antibiotic resistance. Certain naturally occurring clays have been shown to have antimicrobial properties and kill antibiotic resistant bacteria. Harnessing the activity of compounds within these clays that harbor antibiotic properties offers new therapeutic opportunities for fighting the potentially devastating effects of the post antibiotic era. However, natural samples are highly heterogenous and exhibit variable antibacterial effectiveness, therefore synthesizing minerals of high purity with reproducible antibacterial activity is needed. Here we describe for the first time synthetic smectite clay minerals and Fe-sulfide microspheres that reproduce the geochemical antibacterial properties observed in natural occurring clays. We show that these mineral formulations are effective at killing the ESKAPE pathogens (Enterococcus sp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter sp., Pseudomonas aeruginosa and Enterobacter sp.) by maintaining Fe2+ solubility and reactive oxygen species (ROS) production while buffering solution pH, unlike the application of metals alone. Our results represent the first step in utilizing a geochemical process to treat antibiotic resistant topical or gastrointestinal infections in the age of antibiotic resistance.


Subject(s)
Anti-Bacterial Agents/chemical synthesis , Silicates/chemical synthesis , Animals , Drug Resistance, Bacterial , Mice , Microbial Sensitivity Tests , Minerals , NIH 3T3 Cells
6.
Environ Sci Technol ; 55(3): 1626-1636, 2021 02 02.
Article in English | MEDLINE | ID: mdl-33471994

ABSTRACT

Uranium contamination of soils and groundwater in the United States represents a significant health risk and will require multiple remediation approaches. Microbial phosphatase activity coupled to the addition of an organic P source has recently been studied as a remediation strategy that provides an extended release of inorganic P (Pi) into U-contaminated sites, resulting in the precipitation of meta-autunite minerals. Previous laboratory- and field-based biomineralization studies have investigated environments with relatively high U concentrations (>20 µM). However, most contaminated sites have much lower U concentrations (<2 µM). The Environmental Protection Agency (EPA) limit for U in drinking water is 0.126 µM. Reaching this regulatory limit becomes challenging as U concentrations approach autunite solubility. We studied the precipitation of U(VI)-phosphate minerals by an environmental isolate of Caulobacter sp. (strain OR37) from an Oak Ridge, Tennessee, U-contaminated site. Abiotic U(VI) solubility experiments reveal that U(VI)-phosphate minerals do not form in the presence of excess Pi (500 µM) when U(VI) concentrations are <1 µM and pH is <5. When OR37 cells are reacted under the same conditions with Pi or glycerol-2-phosphate, U(VI)-phosphate mineral formation was observed, along with the formation of intracellular polyphosphate granules. These results show that bacteria provide supersaturated microenvironments needed for U(VI)-phosphate mineralization while hydrolyzing organic P sources. This provides a pathway to lower U concentrations to below EPA limits for drinking water.


Subject(s)
Caulobacter , Uranium , Biomineralization , Hydrogen-Ion Concentration , Phosphates , Tennessee , Uranium/analysis
7.
Environ Sci Technol ; 52(11): 6448-6456, 2018 06 05.
Article in English | MEDLINE | ID: mdl-29767970

ABSTRACT

Natural organic matter is known to influence the mobility of plutonium (Pu) in the environment via complexation and reduction mechanisms. Hydroxamate siderophores have been specifically implicated due to their strong association with Pu. Hydroxamate siderophores can also break down into di and monohydroxamates and may influence the Pu oxidation state, and thereby its mobility. In this study we explored the reactions of Pu(VI) and Pu(V) with a monohydroxamate compound (acetohydroxamic acid, AHA) and a trihydroxamate siderophore desferrioxamine B (DFOB) at an environmentally relevant pH (5.5-8.2). Pu(VI) was instantaneously reduced to Pu(V) upon reaction with AHA. The presence of hydroxylamine was not observed at these pHs; however, AHA was consumed during the reaction. This suggests that the reduction of Pu(VI) to Pu(V) by AHA is facilitated by a direct one electron transfer. Importantly, further reduction to Pu(IV) or Pu(III) was not observed, even with excess AHA. We believe that further reduction of Pu(V) did not occur because Pu(V) does not form a strong complex with hydroxamate compounds at a circum-neutral pH. Experiments performed using desferrioxamine B (DFOB) yielded similar results. Broadly, this suggests that Pu(V) reduction to Pu(IV) in the presence of natural organic matter is not facilitated by hydroxamate functional groups and that other natural organic matter moieties likely play a more prominent role.


Subject(s)
Plutonium , Deferoxamine , Hydroxamic Acids , Oxidation-Reduction , Siderophores
8.
Sci Rep ; 6: 19043, 2016 Jan 08.
Article in English | MEDLINE | ID: mdl-26743034

ABSTRACT

Natural antibacterial clays, when hydrated and applied topically, kill human pathogens including antibiotic resistant strains proliferating worldwide. Only certain clays are bactericidal; those containing soluble reduced metals and expandable clay minerals that absorb cations, providing a capacity for extended metal release and production of toxic hydroxyl radicals. Here we show the critical antibacterial components are soluble Fe(2+) and Al(3+) that synergistically attack multiple cellular systems in pathogens normally growth-limited by Fe supply. This geochemical process is more effective than metal solutions alone and provides an alternative antibacterial strategy to traditional antibiotics. Advanced bioimaging methods and genetic show that Al(3+) misfolds cell membrane proteins, while Fe(2+) evokes membrane oxidation and enters the cytoplasm inflicting hydroxyl radical attack on intracellular proteins and DNA. The lethal reaction precipitates Fe(3+)-oxides as biomolecular damage proceeds. Discovery of this bactericidal mechanism demonstrated by natural clays should guide designs of new mineral-based antibacterial agents.


Subject(s)
Aluminum Silicates/pharmacology , Aluminum/pharmacology , Anti-Bacterial Agents/pharmacology , Drug Resistance, Bacterial/drug effects , Escherichia coli Proteins/antagonists & inhibitors , Iron/pharmacology , Aluminum/chemistry , Aluminum Silicates/chemistry , Anti-Bacterial Agents/chemistry , Cations, Divalent , Clay , Drug Resistance, Bacterial/genetics , Escherichia coli/drug effects , Escherichia coli/genetics , Escherichia coli/growth & development , Escherichia coli Proteins/chemistry , Escherichia coli Proteins/genetics , Gene Expression , Humans , Hydrogen Peroxide/chemistry , Hydrogen Peroxide/metabolism , Hydrogen-Ion Concentration , Hydroxyl Radical/chemistry , Hydroxyl Radical/metabolism , Iron/chemistry , Membrane Proteins/antagonists & inhibitors , Membrane Proteins/chemistry , Membrane Proteins/genetics , Methicillin-Resistant Staphylococcus aureus/drug effects , Methicillin-Resistant Staphylococcus aureus/genetics , Methicillin-Resistant Staphylococcus aureus/growth & development , Microbial Sensitivity Tests , Mud Therapy/methods , Oxidation-Reduction , Protein Folding/drug effects , Pseudomonas aeruginosa/drug effects , Pseudomonas aeruginosa/genetics , Pseudomonas aeruginosa/growth & development , Salmonella typhimurium/drug effects , Salmonella typhimurium/genetics , Salmonella typhimurium/growth & development , Staphylococcus epidermidis/drug effects , Staphylococcus epidermidis/genetics , Staphylococcus epidermidis/growth & development
9.
J Bacteriol ; 197(20): 3255-64, 2015 Oct.
Article in English | MEDLINE | ID: mdl-26240069

ABSTRACT

UNLABELLED: The AcrB protein of Escherichia coli, together with TolC and AcrA, forms a contiguous envelope conduit for the capture and extrusion of diverse antibiotics and cellular metabolites. In this study, we sought to expand our knowledge of AcrB by conducting genetic and functional analyses. We began with an AcrB mutant bearing an F610A substitution in the drug binding pocket and obtained second-site substitutions that overcame the antibiotic hypersusceptibility phenotype conferred by the F610A mutation. Five of the seven unique single amino acid substitutions--Y49S, V127A, V127G, D153E, and G288C--mapped in the periplasmic porter domain of AcrB, with the D153E and G288C mutations mapping near and at the distal drug binding pocket, respectively. The other two substitutions--F453C and L486W--were mapped to transmembrane (TM) helices 5 and 6, respectively. The nitrocefin efflux kinetics data suggested that all periplasmic suppressors significantly restored nitrocefin binding affinity impaired by the F610A mutation. Surprisingly, despite increasing MICs of tested antibiotics and the efflux of N-phenyl-1-naphthylamine, the TM suppressors did not improve the nitrocefin efflux kinetics. These data suggest that the periplasmic substitutions act by influencing drug binding affinities for the distal binding pocket, whereas the TM substitutions may indirectly affect the conformational dynamics of the drug binding domain. IMPORTANCE: The AcrB protein and its homologues confer multidrug resistance in many important human bacterial pathogens. A greater understanding of how these efflux pump proteins function will lead to the development of effective inhibitors against them. The research presented in this paper investigates drug binding pocket mutants of AcrB through the isolation and characterization of intragenic suppressor mutations that overcome the drug susceptibility phenotype of mutations affecting the drug binding pocket. The data reveal a remarkable structure-function plasticity of the AcrB protein pertaining to its drug efflux activity.


Subject(s)
Drug Resistance, Multiple, Bacterial , Escherichia coli Proteins/metabolism , Escherichia coli/metabolism , Multidrug Resistance-Associated Proteins/metabolism , Amino Acid Substitution , Anti-Bacterial Agents/pharmacology , Binding Sites , Cephalosporins/metabolism , Computational Biology , Escherichia coli/drug effects , Escherichia coli/genetics , Escherichia coli Proteins/antagonists & inhibitors , Escherichia coli Proteins/genetics , Multidrug Resistance-Associated Proteins/antagonists & inhibitors , Multidrug Resistance-Associated Proteins/genetics , Mutation , Protein Conformation
10.
J Bacteriol ; 197(15): 2479-88, 2015 Aug 01.
Article in English | MEDLINE | ID: mdl-25962916

ABSTRACT

UNLABELLED: The constitutively expressed AcrAB multidrug efflux system of Escherichia coli shows a high degree of homology with the normally silent AcrEF system. Exposure of a strain with acrAB deleted to antibiotic selection pressure frequently leads to the insertion sequence-mediated activation of the homologous AcrEF system. In this study, we used strains constitutively expressing either AcrAB or AcrEF from their normal chromosomal locations to resolve a controversy about whether phenylalanylarginine ß-naphthylamide (PAßN) inhibits the activities of AcrAB and AcrEF and/or acts synergistically with antibiotics by destabilizing the outer membrane permeability barrier. Real-time efflux assays allowed a clear distinction between the efflux pump-inhibiting activity of PAßN and the outer membrane-destabilizing action of polymyxin B nonapeptide (PMXBN). When added in equal amounts, PAßN, but not PMXBN, strongly inhibited the efflux activities of both AcrAB and AcrEF pumps. In contrast, when outer membrane destabilization was assessed by the nitrocefin hydrolysis assay, PMXBN exerted a much greater damaging effect than PAßN. Strong action of PAßN in inhibiting efflux activity compared to its weak action in destabilizing the outer membrane permeability barrier suggests that PAßN acts mainly by inhibiting efflux pumps. We concluded that at low concentrations, PAßN acts specifically as an inhibitor of both AcrAB and AcrEF efflux pumps; however, at high concentrations, PAßN in the efflux-proficient background not only inhibits efflux pump activity but also destabilizes the membrane. The effects of PAßN on membrane integrity are compounded in cells unable to extrude PAßN. IMPORTANCE: The increase in multidrug-resistant bacterial pathogens at an alarming rate has accelerated the need for implementation of better antimicrobial stewardship, discovery of new antibiotics, and deeper understanding of the mechanism of drug resistance. The work carried out in this study highlights the importance of employing real-time fluorescence-based assays in differentiating multidrug efflux-inhibitory and outer membrane-destabilizing activities of antibacterial compounds.


Subject(s)
Bacterial Outer Membrane Proteins/physiology , Cell Membrane/physiology , Escherichia coli/metabolism , Gene Expression Regulation, Bacterial/physiology , Genes, MDR/physiology , Membrane Transport Proteins/physiology , Animals , Anti-Bacterial Agents/pharmacology , Dipeptides/pharmacology , Drug Resistance, Multiple, Bacterial , Escherichia coli/genetics , Gene Expression Regulation, Bacterial/drug effects , Genes, MDR/genetics , Humans , Microbial Sensitivity Tests , Permeability , Phenotype , Polymyxin B/analogs & derivatives , Polymyxin B/pharmacology , Rabbits
11.
Environ Geochem Health ; 36(4): 613-31, 2014 Aug.
Article in English | MEDLINE | ID: mdl-24258612

ABSTRACT

As antibiotic-resistant bacterial strains emerge and pose increased global health risks, new antibacterial agents are needed as alternatives to conventional antimicrobials. Naturally occurring antibacterial clays have been identified which are effective in killing antibiotic-resistant bacteria. This study examines a hydrothermally formed antibacterial clay deposit near Crater Lake, OR (USA). Our hypothesis is that antibacterial clays buffer pH and Eh conditions to dissolve unstable mineral phases containing transition metals (primarily Fe(2+)), while smectite interlayers serve as reservoirs for time release of bactericidal components. Model pathogens (Escherichia coli ATCC 25922 and Staphylococcus epidermidis ATCC 14990) were incubated with clays from different alteration zones of the hydrothermal deposit. In vitro antibacterial susceptibility testing showed that reduced mineral zones were bactericidal, while more oxidized zones had variable antibacterial effect. TEM images showed no indication of cell lysis. Cytoplasmic condensation and cell wall accumulations of <100 nm particles were seen within both bacterial populations. Electron energy loss analysis indicates precipitation of intracellular Fe(3+)-oxide nanoparticles (<10 nm) in E. coli after 24 h. Clay minerals and pyrite buffer aqueous solutions to pH 2.5-3.1, Eh > 630 mV and contain elevated level (mM) of soluble Fe (Fe(2+) and Fe(3+)) and Al(3+). Our interpretation is that rapid uptake of Fe(2+) impairs bacterial metabolism by flooding the cell with excess Fe(2+) and overwhelming iron storage proteins. As the intracellular Fe(2+) oxidizes, it produces reactive oxygen species that damage biomolecules and precipitates Fe-oxides. The ability of antibacterial clays to buffer pH and Eh in chronic non-healing wounds to conditions of healthy skin appears key to their healing potential and viability as an alternative to conventional antibiotics.


Subject(s)
Aluminum Silicates/chemistry , Aluminum Silicates/pharmacology , Anti-Bacterial Agents/pharmacology , Aluminum/pharmacology , Cations/chemistry , Clay , Escherichia coli/drug effects , Hydrogen-Ion Concentration , Iron/analysis , Iron/pharmacology , Microbial Sensitivity Tests , Microscopy, Electron, Scanning Transmission , Minerals/analysis , Oregon , Oxidation-Reduction , Staphylococcus epidermidis/drug effects , Sulfides , X-Ray Diffraction
12.
Hand Clin ; 18(1): 169-78, 2002 Feb.
Article in English | MEDLINE | ID: mdl-12143413

ABSTRACT

The evidence is clear that anatomic reinsertion is the best treatment for an active, compliant patient with an acute distal biceps rupture or a subacute rupture without significant proximal retraction of the tendon. Patients with partial tears and chronic ruptures require surgical attention when persistently symptomatic. Biceps tenodesis through dual incisions or a single anterior incision is a safe, highly reliable, and effective operation. The posterior interosseous nerve is potentially at risk with either approach. This risk is minimized by avoiding exposure and retraction of the nerve. Heterotopic ossification and subsequent proximal radio-ulnar synostosis are reported complications of the two-incision technique. The incidence of this devastating complication has been reduced, but not eliminated, by using a limited posterior forearm muscle-splitting incision and by not exposing the ulna. It is the authors' belief that a single anterior incision with suture anchor fixation of the distal biceps (in the manner described herein) is the surgical treatment of choice for most distal biceps ruptures. Compared with the two-incision method, the posterior interosseous nerve is at no more risk and the chance of heterotopic ossification is diminished. The secure fixation obtained and the limited surgical exposure required allow for early mobilization and rapid return of function.


Subject(s)
Orthopedic Procedures/methods , Rupture/surgery , Tendon Injuries/surgery , Elbow Joint/physiopathology , Elbow Joint/surgery , Humans , Rupture/diagnosis , Rupture/physiopathology , Tendon Injuries/diagnosis , Tendon Injuries/physiopathology , Tendons/anatomy & histology , Tendons/physiology , Elbow Injuries
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