CVD elaboration of nanostructured TiO2-Ag thin films with efficient antibacterial properties

Nanostructured TiO2-Ag composite coatings are deposited by direct liquid injection metal-organic (DLI-MO) CVD at 683K in a one-step process. Silver pivalate (AgPiv) and titanium tetra-iso-propoxide (TTIP) are used as Ag and Ti molecular precursors, respectively. Metallic silver nanoparticles are co-deposited with anatase TiO2 on stainless steel, glass, and silicon wafers. The silver particles are uniformly embedded in the oxide matrix through the entire film thickness. The influence of the growth conditions, including injection parameters, is investigated on the chemical, physical, and structural characteristics of the coatings as well as on their anti-bacterial activities. The bacterium Staphylococcus aureus is employed for anti-bacterial tests. The films are bactericidal, according to the JIS Z 2801 standard test performed in the dark, when they contain less than 1 at.-% of silver. UnderUVirradiation they exhibit a photocatalytic activity which decays by increasing the silver content. As a result of this dual functionality, the TiO2-Ag nanocomposite coatings show promising potentialities as long-term anti-bacterial surfaces since selfcleaning can be achieved periodically under UV light in order to maintain an efficient anti-bacterial activity in the dark or in visible light

Summary of the Workshop on Ecological Effects of Hydrocarbon Spills in Alaska

In any study of the effects of the introduction of an organic compound, such as oil, into a particular environment, such as the Arctic we should, at the outset separate two basic responses: the responses of those organisms (largely bacteria and fungi) to whom the oil is a nutrient to be attacked and eventually decomposed, from the responses of those organisms (largely plants and animals) to whom the oil is a physical and chemical agent of potential toxicity to be tolerated with varying degrees of success. ... both groups really function as mixed populations that exhibit dynamic responses to environmental changes, such as oil spills, but our perception of the effects of these changes is largely population-oriented in the decomposers and species-oriented among higher organisms. ... The actual removal of oil from the Arctic environment depends on a combination of physical weathering and microbial decomposition .... Thus a general principle of microbial ecology is sustained here in that the addition of an organic material to a system stimulates the development of a specific microbial population capable of using that material as a nutrient. The rate of this decomposition process is of maximum importance and it obviously depends on the robustness of the initial microbial population and on nutrient limitation. ... One of the special problems of the Arctic is the very slow rate at which these decomposer populations develop significant activities ... and accessory nutrient supplementations may be required to achieve acceptable rates of hydrocarbon decomposition. A very important facet of oil degradation is the relative rates at which the different components of oil are broken down by bacteria and fungi. ... There are many reasons why oil may be toxic to animals .... Oil appears to constitute a fairly general "contact herbicide" whose direct application is most often toxic to plants. ... plants vary in their sensitivity to this "contact herbicide" and sensitivity mapping ... and bioassays of the sensitivity of specific plants under field conditions are very valuable. ... oil exerts direct and immediate toxic effects on certain plants and animals, in both aquatic and terrestrial systems, and ... more subtle toxic effects are often detected only with the passage of time. Whole populations react in the expected manner in that oil-resistant forms proliferate and then lead the recolonization of the system as the toxic hydrocarbons are removed by weathering or by microbial decomposition. The extent of severe ecological damage from oil spills is, therefore, a function both of the oil-sensitivity of the plant and animal populations and of the rates at which oil is removed by human intervention, weathering or microbial decomposition. ... In the decomposition studies perhaps the most promising development is the advent of rate studies which should be extended to cover the major classes of oil constituents and a very wide variety of ecological systems. ... In many cases it is clear that microbial decomposition, aided by fertilizer application ... will reduce the level of hydrocarbons below the toxic level for the indigenous plants and animals at a satisfactory rate. ... This entire program, with its emphasis on rates of microbial decomposition and on differential sensitivity of both species and populations of higher organisms, is basically well designed and offers a scientific basis for the development ... [of] rational oil spill clean-up policies in the sensitive Alaskan ecosystem

Biofilm on Ventriculo-Peritoneal Shunt Tubing as a Cause of Treatment Failure in Coccidioidal Meningitis

We describe a case of recurrent coccidioidal meningitis in which a fungal biofilm on the tip of ventriculo-peritoneal shunt tubing was likely responsible for a 4-year persistence of Coccidioides immitis, despite the patient’s taking an adequate dosage of fluconazole. Fungal biofilms should be considered as a cause for treatment failure and fungal persistence, especially when artificial prostheses or indwelling catheters are present

Developing a real time sensing system to monitor bacteria in wound dressings

Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing

In Vitro Antimicrobial Effect of a Cold Plasma Jet against Enterococcus faecalis Biofilms

The hypothesis that a cold plasma jet has the antimicrobial effect against Enterococcus faecalis biofilms was tested in vitro. 27 hydroxyapatite discs were incubated with E. faecalis for six days to form a monoculture biofilm on the disc surface. The prepared substrata were divided into three groups: the negative control, the positive control (5.25% NaOCl solution), and the plasma treatment group. Resultant colony-forming unit counts were associated with observations of bacterial cell morphology changes using scanning electron microscopy (SEM). Treatment of E. faecalis biofilm with the plasma and 5.25% NaOCl for 5 min resulted in 93.1% and 90.0% kill (P < 0.0001), respectively. SEM detected that nearly no intact bacteria were discernible for the plasma-exposed HA disc surfaces. The demonstrated bactericidal effect of the plasma with direct surface contact may be due to the enhanced oxidation by the locally produced reactive plasma species

Hydrodynamic dispersion within porous biofilms

Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport

Remote Sensing of Chiral Signatures on Mars

We describe circular polarization as a remote sensing diagnostic of chiral signatures which may be applied to Mars. The remarkable phenomenon of homochirality provides a unique biosignature which can be amenable to remote sensing through circular polarization spectroscopy. The natural tendency of microbes to congregate in close knit communities would be beneficial for such a survey. Observations of selected areas of the Mars surface could reveal chiral signatures and hence explore the possibility of extant or preserved biological material. We describe a new instrumental technique that may enable observations of this form.Comment: 14 pages, 3 figures; to be published in Planetary and Space Scienc

Death and transfiguration in static staphylococcus epidermidis cultures

The overwhelming majority of bacteria live in slime embedded microbial communities termed biofilms, which are typically adherent to a surface. However, when several Staphylococcus epidermidis strains were cultivated in static liquid cultures, macroscopic aggregates were seen floating within the broth and also sedimented at the test tube bottom. Light- and electron microscopy revealed that early-stage aggregates consisted of bacteria and extracellular matrix, organized in sheetlike structures. Perpendicular under the sheets hung a network of periodically arranged, bacteria-associated strands. During the extended cultivation, the strands of a subpopulation of aggregates developed into cross-connected wall-like structures, in which aligned bacteria formed the walls. The resulting architecture had a compartmentalized appearance. In late-stage cultures, the wall-associated bacteria disintegrated so that, henceforth, the walls were made of the coalescing remnants of lysed bacteria, while the compartment-like organization remained intact. At the same time, the majority of strand containing aggregates with associated culturable bacteria continued to exist. These observations indicate that some strains of Staphylococcus epidermidis are able to build highly sophisticated structures, in which a subpopulation undergoes cell lysis, presumably to provide continued access to nutrients in a nutrient-limited environment, whilst maintaining structural integrity

The microbiome of diabetic foot ulcers and the role of biofilms

Diabetic Foot Ulcers are a common precursor to the development of infection and amputations. A breach in the protective skin barrier represents a portal of entry for invading microorganisms, where infective episodes frequently pursue. Three key areas that may augment clinical care are one. understanding what microorganisms are present in Diabetic Foot Ulcers, two. differentiating if microorganisms are planktonic microbial cells or slow growing microbial biofilms and three. treating Diabetic Foot Ulcers complicated by microorganisms with effective topical agents. As part of this thesis, 16S rDNA next generation sequencing was utilised to profile the microbiota of infected Diabetic Foot Ulcers (DFUs). Clinical / laboratory data and treatment outcomes were collected and correlated against microbiota data. Thirty-nine patients with infected DFUs were recruited over twelve-months. Shorter duration DFUs (less than six weeks) all had one dominant bacterial species (n= five of five, 100%, p <⋅001), S. aureus in three cases and S. agalactiae in two. Longer duration DFUs (≥six weeks) were diversely polymicrobial (p = .01) with an average of 63 (range 19-125) bacterial species. Severe Diabetic Foot Infections (DFIs) had complex microbiota’s and were distinctly dissimilar to less severe infections (p = .02), characterised by the presence of low frequency microorganisms. Our results confirm that short DFUs have a simpler microbiota’s consisting of pyogenic cocci but chronic DFUs have a highly polymicrobial microbiota. The duration of a DFU may be useful as a guide to directing antimicrobial therapy. Secondly, we utilised Scanning electron microscopy (SEM) and Fluorescent in situ Hybridisation (FISH) techniques to determine if DFUs were complicated by sessile, slow growing bacteria referred to as biofilms. 65 DFU specimens were obtained from subjects with infected chronic ulcers. Of the 65 DFU specimens evaluated by microscopy, all were characterized as containing biofilm (100%, p < .001). Molecular analyses of DFU specimens revealed diverse polymicrobial communities. No clinical visual cues were identified in aiding clinicians identify wound biofilm. Microscopy visualization when combined with molecular approaches, confirms biofilms are ubiquitous in DFUs and a paradigm shift of managing these complicated wounds needs to consider anti-biofilm strategies. Lastly, the effectiveness of various topical antimicrobials commonly used in woundcare were tested in two separate studies by employing in vitro models, ex vivo porcine skin explant models and in vivo human studies. In the first study, 17 participants with chronic non-healing DFUs due to suspected biofilm involvement were recruited to receive one-week application of Cadexomer Iodine ointment. Real-time qPCR was used to determine the microbial load with 11 participants exhibiting one-two Log10 reductions in microbial load after treatment, in comparison to six patients who experienced less than one log10 reduction (p =.04). Scanning electron microscopy (SEM) and/or fluorescent in situ hybridisation (FISH) confirmed the presence or absence of biofilm in all 17 participants. 16SrDNAnextgenerationsequencing provided useful insights that these wounds support complex polymicrobial communities and demonstrated that Cadexomer Iodine had a broad level of antimicrobial activity in reducing both facultative anaerobes such as Staphylococcus spp., Serratia spp., aerobes including Pseudomonas spp., and obligate anaerobes including Clostridiales family XI. In the second study, a range of topical antimicrobial wound solutions were tested under three different conditions; (in vitro) 4 % w/v melaleuca oil, polyhexamethylene biguanide, chlorhexidine, povidone iodine and hypochlorous acid were tested at short duration exposure times for 15-minutes against three-day mature biofilms of S. aureus and P. aeruginosa. (ex vivo) Hypochlorous acid was tested in a porcine skin explant model with twelve cycles of tenminute exposure, over 24 hours, against three-day mature P. aeruginosa biofilms. (in vivo) 4 % w/v Melaleuca Oil was applied for 15-minutes exposure, daily, for seven days, in ten patients with chronic non-healing Diabetic Foot Ulcers (DFUs) complicated by biofilm. In vitro assessment demonstrated variable efficacy in reducing biofilms ranging between 0.5 log10 reductions to full eradication. Repeated instillation of hypochlorous acid in a porcine model achieved less than one log10 reduction (0.77 log10, p < 0.1). Application of 4 % w/v melaleuca oil in vivo, resulted in no change to the total microbial load of DFUs complicated by biofilm (median log10 microbial load pre-treatment = 4.9 log10 versus 4.8 log10 (p = .43). In conclusion, to the best of our knowledge, the in vivo human studies testing the performances of topical antimicrobials represents the first in vivo evidence employing a range of molecular and microscopy techniques. These demonstrate the ability of Cadexomer Iodine (sustained release over 48-72 hours) to reduce the microbial load of chronic non-healing DFUs complicated by biofilm. In contrast, short durations of exposure to topical antimicrobial wound solutions commonly utilised by clinicians are ineffective against microbial biofilms, particularly when used in vivo

Chitosan-Cellulose Composite for Wound Dressing Material. Part 2. Antimicrobial Activity, Blood Absorption Ability, and Biocompatibility

Chitosan (CS), a polysaccharide derived from chitin, the second most abundant polysaccharide, is widely used in the medical world because of its natural and nontoxic properties and its innate ability for antibacterial and hemostasis effects. In this study, the novel composites containing CS and cellulose (CEL) (i.e., [CEL + CS]), which we have previously synthesized using a green and totally recyclable method, were investigated for their antimicrobial activity, absorption of anticoagulated whole blood, anti-inflammatory activity through the reduction of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and the biocompatibility with human fibroblasts. The [CEL + CS] composites were found to inhibit the growth of both Gram positive and negative micro-organisms. For examples, the regenerated 100% lyophilized chitosan material was found to reduce growth of Escherichia coli (ATCC 8739 and vancomycin resistant Enterococcus faecalis (ATCC 51299) by 78, 36, and 64%, respectively. The composites are nontoxic to fibroblasts; that is, fibroblasts, which are critical to the formation of connective tissue matrix were found to grow and proliferate in the presence of the composites. They effectively absorb blood, and at the same rate and volume as commercially available wound dressings. The composites, in both air-dried and lyophilized forms, significantly inhibit the production of TNF-α and IL-6 by stimulated macrophages. These results clearly indicate that the biodegradable, biocompatible and nontoxic [CEL + CS] composites, particularly those dried by lyophilizing, can be effectively used as a material in wound dressings