The early detection of wound infection in situ can dramatically improve patient care pathways and clinical outcomes. There is increasing evidence that within an infected wound the main bacterial mode of living is a biofilm: a confluent community of adherent bacteria encased in an extracellular polymeric matrix. Here we have reported the development of a prototype wound dressing, which switches on a fluorescent color when in contact with pathogenic wound biofilms. The dressing is made of a hydrated agarose film in which the fluorescent dye containing vesicles were mixed with agarose and dispersed within the hydrogel matrix. The static and dynamic models of wound biofilms, from clinical strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis, were established on nanoporous polycarbonate membrane for 24, 48, and 72 h, and the dressing response to the biofilms on the prototype dressing evaluated. The dressing indicated a clear fluorescent/color response within 4 h, only observed when in contact with biofilms produced by a pathogenic strain. The sensitivity of the dressing to biofilms was dependent on the species and strain types of the bacterial pathogens involved, but a relatively higher response was observed in strains considered good biofilm formers. There was a clear difference in the levels of dressing response, when dressings were tested on bacteria grown in biofilm or in planktonic cultures, suggesting that the level of expression of virulence factors is different depending of the growth mode. Colorimetric detection on wound biofilms of prevalent pathogens (S. aureus, P. aeruginosa, and E. faecalis) is also demonstrated using an ex vivo porcine skin model of burn wound infection.

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

We describe a novel infection-responsive coating for urinary catheters that provides a clear visual early warning of Proteus mirabilis infection and subsequent blockage. The crystalline biofilms of P. mirabilis can cause serious complications for patients undergoing long-term bladder catheterisation. Healthy urine is around pH 6, bacterial urease increases urine pH leading to the precipitation of calcium and magnesium deposits from the urine, resulting in dense crystalline biofilms on the catheter surface that blocks urine flow. The coating is a dual layered system in which the lower poly(vinyl alcohol) layer contains the self-quenching dye carboxyfluorescein. This is capped by an upper layer of the pH responsive polymer poly(methyl methacrylate-co-methacrylic acid) (Eudragit S100®). Elevation of urinary pH (>pH 7) dissolves the Eudragit layer, releasing the dye to provide a clear visual warning of impending blockage. Evaluation of prototype coatings using a clinically relevant in vitro bladder model system demonstrated that coatings provide up to 12 h advanced warning of blockage, and are stable both in the absence of infection, and in the presence of species that do not cause catheter blockage. At the present time, there are no effective methods to control these infections or provide warning of impending catheter blockage.

The use of hydrogels as safe, biocompatible materials for wound healing has been widely utilized in recent years. Here, we investigated the use of a composite hydrogel to impart a "trigger" mechanism into an antimicrobial hydrogel system. The system was comprised of a bilayer hydrogel architecture: a lower agarose layer containing the antimicrobial virus Bacteriophage K (ΦK) and an upper layer formed of photo-cross-linkable hyaluronic acid methacrylate (HAMA) which creates the hydrogel trigger. This trigger is sensitive to the enzyme hyaluronidase, an enzyme known to be secreted by the majority of Staphylococcus aureus strains. In the presence of hyaluronidase, HAMA is degraded, releasing ΦK into the surrounding environment which consequently go on to kill surrounding bacteria. Our results show that on incubation with hyaluronidase (purified or from S. aureus), large pores form in HAMA as degradation goes on, which facilitates ΦK release.

Wound infection is commonly observed after surgery and trauma but is difficult to diagnose and poorly defined in terms of objective clinical parameters. The assumption that bacteria in a wound correlate with infection is false; all wounds contain microorganisms, but not all wounds are clinically infected. This makes it difficult for clinicians to determine true wound infection, especially in wounds with pathogenic biofilms. If an infection is not properly treated, pathogenic virulence factors, such as rhamnolipids from Pseudomonas aeruginosa , can modulate the host immune response and cause tissue breakdown. Life-threatening sepsis can result if the organisms penetrate deep into host tissue. This communication describes the sensor development for five important clinical microbial pathogens commonly found in wounds: Staphylococcus aureus , P. aeruginosa , Candida albicans/auris, and Enterococcus faecalis (the SPaCE pathogens). The sensor contains liposomes encapsulating a self-quenched fluorescent dye. Toxins, expressed by SPaCE infecting pathogens in early-stage infected wounds, break down the liposomes, triggering dye release, thus changing the sensor color from yellow to green, an indication of infection. Five clinical species of bacteria and fungi, up to 20 strains each (totaling 83), were grown as early-stage biofilms in ex vivo porcine burn wounds. The biofilms were then swabbed, and the swab placed in the liposome suspension. The population density of selected pathogens in a porcine wound biofilm was quantified and correlated with colorimetric response. Over 88% of swabs switched the sensor on (10 7 –10 8 CFU/swab). A pilot clinical study demonstrated a good correlation between sensor switch-on and early-stage wound infection.

This work presents an electrochemical sensor concept for bacterial toxin detection using biomimetic lipid vesicles containing potassium ferricyanide. The toxin mediated release of redox couples from the vesicles was quantified by measuring the redox current on screen printed electrodes, and the detection limits to rhamnolipid, delta toxin and bacterial supernatants from clinical wound pathogens were examined. Overall detection limits of both redox and carboxyfluorescein containing vesicles were one order of magnitude lower than the cytotoxic dose of studied toxins to T lymphocytes.

Formation of crystalline biofilms following infection by Proteus mirabilis can lead to encrustation and blockage of long-term indwelling catheters, with serious clinical consequences. We describe a simple sensor, placed within the catheter drainage bag, to alert of impending blockage via a urinary color change. The pH-responsive sensor is a dual-layered polymeric "lozenge", able to release the self-quenching dye 5(6)-carboxyfluorescein in response to the alkaline urine generated by the expression of bacterial urease. Sensor performance was evaluated within a laboratory model of the catheterized urinary tract, infected with both urease positive and negative bacterial strains under conditions of established infection, achieving an average "early warning" of catheter blockage of 14.5 h. Signaling only occurred following infection with urease positive bacteria. Translation of these sensors into a clinical environment would allow appropriate intervention before the occurrence of catheter blockage, a problem for which there is currently no effective control method.

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