Inhibition of Pseudomonas aeruginosa biofilm formation on wound dressings

Chronic nonhealing skin wounds often contain bacterial biofilms that prevent normal wound healing and closure and present challenges to the use of conventional wound dressings. We investigated inhibition of Pseudomonas aeruginosa biofilm formation, a common pathogen of chronic skin wounds, on a commercially available biological wound dressing. Building on prior reports, we examined whether the amino acid tryptophan would inhibit P. aeruginosa biofilm formation on the three‐dimensional surface of the biological dressing. Bacterial biomass and biofilm polysaccharides were quantified using crystal violet staining or an enzyme linked lectin, respectively. Bacterial cells and biofilm matrix adherent to the wound dressing were visualized through scanning electron microscopy. d ‐/l ‐tryptophan inhibited P. aeruginosa biofilm formation on the wound dressing in a dose dependent manner and was not directly cytotoxic to immortalized human keratinocytes although there was some reduction in cellular metabolism or enzymatic activity. More importantly, d ‐/l ‐tryptophan did not impair wound healing in a splinted skin wound murine model. Furthermore, wound closure was improved when d ‐/l ‐tryptophan treated wound dressing with P. aeruginosa biofilms were compared with untreated dressings. These findings indicate that tryptophan may prove useful for integration into wound dressings to inhibit biofilm formation and promote wound healing.     

A study on the ability of quaternary ammonium groups attached to a polyurethane foam wound dressing to inhibit bacterial attachment and biofilm formation

Bacterial infection of acute and chronic wounds impedes wound healing significantly. Part of this impediment is the ability of bacterial pathogens to grow in wound dressings. In this study, we examined the effectiveness of a polyurethane (PU) foam wound dressings coated with poly diallyl‐dimethylammonium chloride (pDADMAC‐PU) to inhibit the growth and biofilm development by three main wound pathogens, Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii, within the wound dressing. pDADMAC‐PU inhibited the growth of all three pathogens. Time‐kill curves were conducted both with and without serum to determine the killing kinetic of pDADMAC‐PU. pDADMAC‐PU killed S. aureus, A. baumannii, and P. aeruginosa. The effect of pDADMAC‐PU on biofilm development was analyzed quantitatively and qualitatively. Quantitative analysis, colony‐forming unit assay, revealed that pDADMAC‐PU dressing produced more than eight log reduction in biofilm formation by each pathogen. Visualization of the biofilms by either confocal laser scanning microscopy or scanning electron microscopy confirmed these findings. In addition, it was found that the pDADMAC‐PU‐treated foam totally inhibited migration of bacteria through the foam for all three bacterial strains. These results suggest that pDADMAC‐PU is an effective wound dressing that inhibits the growth of wound pathogens both within the wound and in the wound dressing.     

Noncontact,low‐frequency ultrasound as an effective therapy against Pseudomonas aeruginosa–infected biofilm wounds

Bacterial biofilms, a critical chronic wound mediator, remain difficult to treat. Energy‐based devices may potentially improve healing, but with no evidence of efficacy against biofilms. This study evaluates noncontact, low‐frequency ultrasound (NLFU) in the treatment of biofilm‐infected wounds. Six‐millimeter dermal punch wounds in rabbit ears were inoculated with 10⁷ colony‐forming units of Pseudomonas aeruginosa or left as sterile controls. A biofilm was established in vivo using our published model. NLFU treatment was carried out every other day or every day, with contralateral ear wounds acting as internal, untreated controls. Wounds were harvested for several quantitative endpoints and scanning electron microscopy to evaluate the biofilm structure. The P. aeruginosa biofilm consistently impaired wound epithelialization and granulation. NLFU, both every other day and every day, improved healing and reduced bacterial counts relative to untreated controls (p < 0.05). Scanning electron microscopy confirmed a qualitative decrease in bacteria after both treatments. NLFU also reduced inflammatory cytokine expression (p < 0.05). Our study suggests that NLFU is an effective therapy against P. aeruginosa wound biofilm. This represents the first in vivo evidence of energy‐based modalities' impact on wound biofilm, setting the foundation for future mechanistic studies. Continued wound care technology research is essential to improving our understanding, and treatment, of biofilm‐infected chronic wounds.     

The wound‐healing effects of a next‐generation anti‐biofilm silver Hydrofiber wound dressing on deep partial‐thickness wounds using a porcine model

Topical antimicrobials are widely used to control wound bioburden and facilitate wound healing; however, the fine balance between antimicrobial efficacy and non‐toxicity must be achieved. This study evaluated whether an anti‐biofilm silver‐containing wound dressing interfered with the normal healing process in non‐contaminated deep partial thickness wounds. In an in‐vivo porcine wound model using 2 pigs, 96 wounds were randomly assigned to 1 of 3 dressing groups: anti‐biofilm silver Hydrofiber dressing (test), silver Hydrofiber dressing (control), or polyurethane film dressing (control). Wounds were investigated for 8 days, and wound biopsies (n = 4) were taken from each dressing group, per animal, on days 2, 4, 6, and 8 after wounding and evaluated using light microscopy. No statistically significant differences were observed in the rate of reepithelialisation, white blood cell infiltration, angiogenesis, or granulation tissue formation following application of the anti‐biofilm silver Hydrofiber dressing versus the 2 control dressings. Overall, epithelial thickness was similar between groups. Some differences in infiltration of specific cell types were observed between groups. There were no signs of tissue necrosis, fibrosis, or fatty infiltration in any group. An anti‐biofilm silver Hydrofiber wound dressing did not cause any notable interference with normal healing processes.     

Time course study of delayed wound healing in a biofilm‐challenged diabetic mouse model

Bacterial biofilm has been shown to play a role in delaying wound healing of chronic wounds, a major medical problem that results in significant health care burden. A reproducible animal model could be very valuable for studying the mechanism and management of chronic wounds. Our previous work showed that Pseudomonas aeruginosa (PAO1) biofilm challenge on wounds in diabetic (db/db) mice significantly delayed wound healing. In this wound time course study, we further characterize the bacterial burden, delayed wound healing, and certain aspects of the host inflammatory response in the PAO1 biofilm‐challenged db/db mouse model. PAO1 biofilms were transferred onto 2‐day‐old wounds created on the dorsal surface of db/db mice. Control wounds without biofilm challenge healed by 4 weeks, consistent with previous studies; none of the biofilm‐challenged wounds healed by 4 weeks. Of the biofilm‐challenged wounds, 64% healed by 6 weeks, and all of the biofilm‐challenged wounds healed by 8 weeks. During the wound‐healing process, P. aeruginosa was gradually cleared from the wounds while the presence of Staphylococcus aureus (part of the normal mouse skin flora) increased. Scabs from all unhealed wounds contained 10⁷ P. aeruginosa, which was 100‐fold higher than the counts isolated from wound beds (i.e., 99% of the P. aeruginosa was in the scab). Histology and genetic analysis showed proliferative epidermis, deficient vascularization, and increased inflammatory cytokines. Hypoxia inducible factor expression increased threefold in 4‐week wounds. In summary, our study shows that biofilm‐challenged wounds typically heal in approximately 6 weeks, at least 2 weeks longer than nonbiofilm‐challenged normal wounds. These data suggest that this delayed wound healing model enables the in vivo study of bacterial biofilm responses to host defenses and the effects of biofilms on host wound healing pathways. It may also be used to test antibiofilm strategies for treating chronic wounds.     

The ability of quaternary ammonium groups attached to a urethane bandage to inhibit bacterial attachment and biofilm formation in a mouse wound model

For proper wound healing, control of bacteria or bacterial infections is of major importance. While caring for a wound, dressing material plays a key role as bacteria can live in the bandage and keep re‐infecting the wound. They do this by forming biofilms in the bandage, which slough off planktonic bacteria and overwhelm the host defense. It is thus necessary to develop a wound dressing that will inhibit bacterial growth. This study examines the effectiveness of a polyurethane foam wound dressing bound with polydiallyl‐dimethylammonium chloride (pDADMAC) to inhibit the growth of bacteria in a wound on the back of a mouse. This technology does not allow pDADMAC to leach away from the dressing into the wound, thereby preventing cytotoxic effects. Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii were chosen for the study to infect the wounds. S. aureus and P. aeruginosa are important pathogens in wound infections, while A. baumannii was selected because of its ability to acquire or upregulate antibiotic drug resistance determinants. In addition, two different isolates of methicillin‐resistant S. aureus (MRSA) were tested. All the bacteria were measured in the wound dressing and in the wound tissue under the dressing. Using colony‐forming unit (CFU) assays, over six logs of inhibition (100%) were found for all the bacterial strains using pDADMAC‐treated wound dressing when compared with control‐untreated dressing. The CFU assay results obtained with the tissues were significant as there were 4–5 logs of reduction (100%) of the test organism in the tissue of the pDADMAC‐covered wound versus that of the control dressing‐covered wound. As the pDADMAC cannot leave the dressing (like other antimicrobials), this would imply that the dressing acts as a reservoir for free bacteria from a biofilm and plays a significant role in the development of a wound infection.     

Impact of a novel,antimicrobial dressing on in vivo,Pseudomonas aeruginosa wound biofilm: Quantitative comparative analysis using a rabbit ear model

The importance of bacterial biofilms to chronic wound pathogenesis is well established. Different treatment modalities, including topical dressings, have yet to show consistent efficacy against wound biofilm. This study evaluates the impact of a novel, antimicrobial Test Dressing on Pseudomonas aeruginosa biofilm‐infected wounds. Six‐mm dermal punch wounds in rabbit ears were inoculated with 10⁶ colony‐forming units of P. aeruginosa. Biofilm was established in vivo using our published model. Dressing changes were performed every other day with either Active Control or Test Dressings. Treated and untreated wounds were harvested for several quantitative endpoints. Confirmatory studies were performed to measure treatment impact on in vitro P. aeruginosa and in vivo polybacterial wounds containing P. aeruginosa and Staphylococcus aureus. The Test Dressing consistently decreased P. aeruginosa bacterial counts, and improved wound healing relative to Inactive Vehicle and Active Control wounds (p < 0.05). In vitro bacterial counts were also significantly reduced following Test Dressing therapy (p < 0.05). Similarly, improvements in bacterial burden and wound healing were also achieved in polybacterial wounds (p < 0.05). This study represents the first quantifiable and consistent in vivo evidence of a topical antimicrobial dressing's impact against established wound biofilm. The development of clinically applicable therapies against biofilm such as this is critical to improving chronic wound care.     

Efficacy of a surfactant‐based wound dressing on biofilm control

The aim of this study was to evaluate the efficacy of both a nonantimicrobial and antimicrobial (1% silver sulfadiazine—SSD) surfactant‐based wound dressing in the control of Pseudomonas aeruginosa, Enterococcus sp, Staphylococcus epidermidis, Staphylococcus aureus, and methicillin‐resistant S. aureus (MRSA) biofilms. Anti‐biofilm efficacy was evaluated in numerous adapted American Standards for Testing and Materials (ASTM) standard biofilm models and other bespoke biofilm models. The ASTM standard models employed included the Minimum biofilm eradication concentration (MBEC) biofilm model (ASTM E2799) and the Centers for Disease Control (CDC) biofilm reactor model (ASTM 2871). Such bespoke biofilm models included the filter biofilm model and the chamberslide biofilm model. Results showed complete kill of microorganisms within a biofilm using the antimicrobial surfactant‐based wound dressing. Interestingly, the nonantimicrobial surfactant‐based dressing could disrupt existing biofilms by causing biofilm detachment. Prior to biofilm detachment, we demonstrated, using confocal laser scanning microscopy (CLSM), the dispersive effect of the nonantimicrobial surfactant‐based wound dressing on the biofilm within 10 minutes of treatment. Furthermore, the non‐antimicrobial surfactant‐based wound dressing caused an increase in microbial flocculation/aggregation, important for microbial concentration. In conclusion, this nonantimicrobial surfactant‐based wound dressing leads to the effective detachment and dispersion of in vitro biofilms. The use of surfactant‐based wound dressings in a clinical setting may help to disrupt existing biofilm from wound tissue and may increase the action of antimicrobial treatment.     

Povidone‐iodine ointment demonstrates in vitro efficacy against biofilm formation

Anti‐infectives used to treat chronic exuding wounds are diluted by wound exudates, absorbed into dressings, metabolised by proteases and destroyed by pH. In order to mimic such effects of exudates, the efficacy of six topical wound agents was assessed undiluted and at 10% concentrations, including povidone‐iodine ointment and a silver‐impregnated wound dressing, to remove biofilms of Pseudomonas aeruginosa, multi‐species biofilms of Candida albicans and methicillin‐resistant Staphylococcus aureus (MRSA) in vitro in a Centers for Disease Control and Prevention (CDC) reactor. Povidone‐iodine was also diluted to 3·3% and 33·3% of the commercial concentrations. Viable microorganisms in each preparation were quantified by colony count. No viable P. aeruginosa biofilm material was recovered after 4 and 24 hours of treatment with povidone‐iodine ointment at the 100% and 10% concentrations. No C. albicans/MRSA biofilm material was recovered after 4 and 24 hours of treatment with povidone‐iodine ointment at the 100% concentration. In general, following dilution, povidone‐iodine ointment appeared to exhibit greater biofilm removal than the other agents tested. Further research involving different microorganisms in vitro and in vivo over a longer period of time will help elucidate the full potential of povidone‐iodine ointment and liposomal hydrogel.     

A PEGylated fibrin hydrogel‐based antimicrobial wound dressing controls infection without impeding wound healing

Combat injuries are associated with a high incidence of infection, and there is a continuing need for improved approaches to control infection and promote wound healing. Due to the possible local and systemic adverse effects of standard 1% cream formulation (Silvadene), we had previously developed a polyethylene glycol (PEGylated) fibrin hydrogel (FPEG)‐based wound dressing for the controlled delivery of silver sulfadiazine (SSD) entrapped in chitosan microspheres (CSM). In this study, we have evaluated the antimicrobial and wound healing efficacy of SSD‐CSM‐FPEG using a full‐thickness porcine wound infected with Pseudomonas aeruginosa. Infected wounds treated with a one‐time application of the SSD‐CSM‐FPEG wound dressing demonstrated significantly reduced bacterial bioburden over time (99·99% of reduction by day 11; P < 0·05) compared with all the other treatment groups. The epithelial thickness and granulation of the wound bed was significantly better on day 7 (150·9 ± 13·12 µm), when compared with other treatment groups. Overall, our findings demonstrate that the SSD‐CSM‐FPEG wound dressing effectively controls P. aeruginosa infection and promotes wound healing by providing a favourable environment that induces neovascularisation. Collectively, sustained release of SSD using fibrin hydrogel exhibited enhanced benefits when compared with the currently available SSD treatment, and this may have significant implications in the bacterial reduction of infected wounds in military and civilian populations.     

A prospective randomised open label study to evaluate the potential of a new silver alginate/carboxymethylcellulose antimicrobial wound dressing to promote wound healing

The aim of this study was to observe both the clinical signs and symptoms of wounds at risk of infection, that is critically colonised (biofilm infected) and antimicrobial‐performance of an ionic silver alginate/carboxymethylcellulose (SACMC) dressing, in comparison with a non silver calcium alginate fibre (AF) dressing, on chronic venous leg and pressure ulcers. Thirty‐six patients with venous or pressure ulcers, considered clinically to be critically colonised (biofilm infected), were randomly chosen to receive either an SACMC dressing or a non silver calcium AF dressing. The efficacy of each wound dressing was evaluated over a 4‐week period. The primary study endpoints were prevention of infection and progression to wound healing. The SACMC group showed a statistically significant (P = 0·017) improvement to healing as indicated by a reduction in the surface area of the wound, over the 4‐week study period, compared with AF controls. In conclusion, the SACMC dressing showed a greater ability to prevent wounds progressing to infection when compared with the AF control dressing. In addition, the results of this study also showed an improvement in wound healing for SACMC when compared with a non silver dressing.     

Cadexomer iodine provides superior efficacy against bacterial wound biofilms in vitro and in vivo

Examination of clinical samples indicates bacterial biofilms are present in the majority of chronic wounds, and substantial evidence suggests biofilms contribute significantly to delayed healing. Bacteria in biofilms are highly tolerant of antimicrobials, and little data exist to guide the choice of anti‐biofilm wound therapy. Cadexomer iodine (CI) was recently reported to have superior efficacy compared to diverse wound dressings against Pseudomonas aeruginosa biofilms in an ex vivo model. In the current study, the strong performance of CI vs. P. aeruginosa biofilm was confirmed using colony and colony drip‐flow in vitro wound biofilm models. Similar in vitro efficacy of CI was also demonstrated against mature Staphylococcus aureus biofilms using the same models. Additionally, the rapid kill of mature S. aureus and P. aeruginosa colony biofilms was visualized by confocal microscopy using Live/Dead fluorescent stains. Superior in vitro efficacy of CI vs. staphylococcal biofilms was further demonstrated against methicillin‐resistant S. aureus (MRSA) using multiple biofilm models with log reduction, Live/Dead, and metabolic endpoints. Comparator antimicrobial dressings, including silver‐based dressings used throughout and other active agents used in individual models, elucidated only limited effects against the mature biofilms. Given the promising in vitro activity, CI was tested in an established mouse model of MRSA wound biofilm. CI had significantly greater impact on MRSA biofilm in mouse wounds than silver dressings or mupirocin based on Gram‐stained histology sections and quantitative microbiology from biopsy samples (>4 log reduction in CFU/g vs. 0.7–1.6, p < 0.0001). The superior efficacy for CI in these in vitro and in vivo models suggests CI topical products may represent a better choice to address established bacterial biofilm in chronic wounds.     

Pseudomonas aeruginosa uses T3SS to inhibit diabetic wound healing

Diabetic foot ulcers are responsible for more hospitalizations than any other complication of diabetes. Bacterial infection is recognized as an important factor associated with impaired healing in diabetic ulcers. Pseudomonas aeruginosa is the most frequently detected Gram‐negative pathogen in diabetic ulcers. P. aeruginosa infection has been shown to impair healing in diabetic wounds in a manner that correlates with its ability to form biofilm. While the majority of infections in diabetic ulcers are biofilm associated, 33% of infections are nonbiofilm in nature. P. aeruginosa is the most prevalent Gram‐negative pathogen in all diabetic wound types, which suggests that the deleterious impact of P. aeruginosa on healing in diabetic wounds goes beyond its ability to form biofilm and likely involves other factors. The Type III Secretion System (T3SS) virulence structure is required for the pathogenesis of all P. aeruginosa clinical isolates, suggesting that it may also play a role in the inhibition of wound repair in diabetic skin ulcers. We evaluated the role of T3SS in mediating P. aeruginosa–induced tissue damage in the wounds of diabetic mice. Our data demonstrate that P. aeruginosa establishes a robust and persistent infection in diabetic wounds independent of its ability to form biofilm and causes severe wound damage in a manner that primarily depends on its T3SS.     

The effect and safety of dressing composed by nylon threads covered with metallic silver in wound treatment

Silver is used worldwide in dressings for wound management. Silver has demonstrated great efficacy against a broad range of microorganisms, but there is very little data about the systemic absorption and toxicity of silver in vivo. In this study, the antimicrobial effect of the silver‐coated dressing (SilverCoat®) was evaluated in vitro against the most common microorganisms found in wounds, including Pseudomonas aeruginosa, Candida albicans, Staphylococcus aureus, Methicillin‐resistant Staphylococcus aureus and Klebsiella pneumoniae. We also performed an excisional skin lesion assay in mice to evaluate wound healing after 14 days of treatment with a silver‐coated dressing, and we measured the amount of silver in the blood, the kidneys and the liver after treatment. Our data demonstrated that the nylon threads coated with metallic silver have a satisfactory antimicrobial effect in vitro, and the prolonged use of these threads did not lead to systemic silver absorption, did not induce toxicity in the kidneys and the liver and were not detrimental to the normal wound‐healing process.     

Effectiveness of a polyhexanide irrigation solution on methicillin‐resistant Staphylococcus aureus biofilms in a porcine wound model

Irrigation and removal of necrotic debris can be beneficial for proper healing. It is becoming increasingly evident that wounds colonized with biofilm forming bacteria, such as Staphylococcus aureus (SA), can be more difficult to eradicate. Here we report our findings of the effects of an irrigation solution containing propyl‐betaine and polyhexanide (PHMB) on methicillin‐resistant Staphylococcus aureus (MRSA) biofilms in a porcine wound model. Thirty‐nine deep partial thickness wounds were created with six wounds assigned to one of six treatment groups: (i) PHMB, (ii) Ringer's solution, (iii) hypochlorous acid/sodium hypochlorite, (iv) sterile water, (v) octenidine dihydrochloride, and (vi) octenilin. Wounds were inoculated with MRSA and covered with a polyurethane dressing for 24 hours to allow biofilm formation. The dressings were then removed and the wounds were irrigated twice daily for 3 days with the appropriate solution. MRSA from four wounds were recovered from each treatment group at 3 days and 6 days hours after initial treatment. Irrigation of wounds with the PHMB solution resulted in 97·85% and 99·64% reductions of MRSA at the respective 3 days and 6 days assessment times when compared to the untreated group. Both of these reductions were statistically significant compared to all other treatment groups (P values <0·05).     

Controlling Methicillin Resistant Staphyloccocus aureus and Pseudomonas aeruginosa Wound Infections with a Novel Biomaterial

Wound infections, especially those associated with methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa, offer considerable challenges for clinicians. Our laboratory has recently developed novel composite biomaterials (DRDC) for wound dressing applications, and demonstrated their in vitro bactericidal efficacy. In the present study, we assessed the proliferation of planktonic and sessile Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus in porcine full-thickness wounds covered for up to 48 h with either saline- or mafenide acetate-loaded DRDC puffs and meshes. All biomaterials were applied 4 h following bacterial inoculation of the wounds with methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa, to allow colonization of the tissues and initiation of biofilm formation. The drug-loaded biomaterials eradicated both the planktonic and biofilm bacteria in the wounds within 24 h (p <. 05), irrespective of the bacterial strain or architecture of the dressing. While the wound bioburdens increased in the ensuing 24 h, they remained approximately 2 log₁₀ colony-forming units (CFU) below (p <. 05) their respective baseline values. Similarly, less than 4 log₁₀ CFU was recovered in the drug-loaded DRDC biomaterials throughout the study. These data show that the DRDC puffs and meshes are effective in delivering certain medications, such as antimicrobial agents, to the wound bed, suggesting considerable value of this material for treating wounds, especially those with irregular shapes, contours, and depths.     

Use of flow cytometry to compare the antimicrobial efficacy of silver‐containing wound dressings against planktonic Staphylococcus aureus and Pseudomonas aeruginosa

Silver‐impregnated wound dressings continue to be routinely used for the management of infected wounds, or wounds that are at risk of becoming infected. The ability of antimicrobials that have been incorporated into wound dressings to kill microorganisms within the dressing requires appropriate evaluation using in vitro models. In vitro models that have been exploited for this purpose have included the corrected zone of inhibition and the log reduction assay. However, these and other related culturable‐based assays are purported to have poor correlation with the overall microbicidal barrier activity of an antimicrobial wound dressing. This is because culturable‐based methods only retrospectively indicate bacterial cell death and do not take into account viable but nonculturable states of microorganisms. Consequently, it was the purpose of this study to show that the use of flow cytometry, in conjunction with Syto^® 9 and propidium iodide, could be used as a method for accurately evaluating and comparing the antimicrobial barrier efficacy of a silver alginate and a silver carboxymethyl cellulose dressing on individual bacterial cells without the need for the use of culturable assays. When a comparison of antimicrobial barrier efficacy on individual planktonic Staphylococcus aureus cells in a simulated wound fluid assay was made between each dressing, enhanced antimicrobial efficacy (as showed by the percentage of dead to alive bacterial cells) of the silver alginate dressing was shown. When Pseudomonas aeruginosa was exposed to both silver‐containing dressings, equivalent kill rates were showed for up to 4 days. This result was not significantly different (p<0.05). By utilizing the use of flow cytometric assays, the antimicrobial barrier efficacy of wound dressings can be accurately evaluated enabling differentiation to be achieved between individual dead and live bacteria. The flow cytometric assay is considered a significant advancement to the traditionally used culturable‐based methods that are presently used for antimicrobial barrier efficacy testing on planktonic microorganisms.     

The visualisation and speed of kill of wound isolates on a silver alginate dressing

In chronic wound management, alginate dressings are used to absorb exudate and reduce the microbial burden. Silver alginate offers the added benefit of an additional antimicrobial pressure on contaminating microorganisms. This present study compares the antimicrobial activity of a RESTORE silver alginate dressing with a silver‐free control dressing using a combination of in vitro culture and imaging techniques. The wound pathogens examined included Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, β‐haemolytic Streptococcus, and strictly anaerobic bacteria. The antimicrobial efficacy of the dressings was assessed using log₁₀ reduction and 13‐day corrected zone of inhibition (CZOI) time‐course assays. Confocal laser scanning microscopy (CLSM) was used to visualise the relative proportions of live/dead microorganisms sequestered into the dressings over 24 hours and estimate the comparative speed of kill. The RESTORE silver alginate dressing showed significantly greater log₁₀ reductions and CZOIs for all microorganisms compared with the control, indicating the antimicrobial effect of ionic silver. Antimicrobial activity was evident against all test organisms for up to 5 days and, in some cases, up to 12 days following an on‐going microbial challenge. Imaging bacteria sequestered in the silver‐free dressing showed that each microbial species aggregated in the dressing and remained viable for more than 20 hours. Growth was not observed inside of the dressing, indicating a possible microbiostatic effect of the alginate fibres. In comparison, organisms in the RESTORE silver alginate dressing were seen to lose viability at a considerably greater rate. After 16 hours of contact with the RESTORE silver alginate dressing, >90% of cells of all bacteria and yeast were no longer viable. In conclusion, collectively, the data highlights the rapid speed of kill and antimicrobial suitability of this RESTORE silver alginate dressing on wound isolates and highlights its overwhelming ability to manage a microbial wound bioburden in the management of infected wounds.     

Pseudomonas aeruginosa biofilm hampers murine central wound healing by suppression of vascular epithelial growth factor

Biofilm‐infected wounds are clinically challenging. Vascular endothelial growth factor and host defence S100A8/A9 are crucial for wound healing but may be suppressed by biofilms. The natural course of Pseudomonas aeruginosa biofilm infection was compared in central and peripheral zones of burn‐wounded, infection‐susceptible BALB/c mice, which display delayed wound closure compared to C3H/HeN mice. Wounds were evaluated histopathologically 4, 7 or 10 days post‐infection. Photoplanimetry evaluated necrotic areas. P. aeruginosa biofilm suppressed vascular endothelial growth factor levels centrally in BALB/c wounds but increased peripheral levels 4–7 days post‐infection. Central zones of the burn wound displayed lower levels of central vascular endothelial growth factor as observed 4 and 7 days post‐infection in BALB/c mice compared to their C3H/HeN counterparts. Biofilm suppressed early, centrally located S100A8/A9 in BALB/c and centrally and peripherally later on in C3H/HeN wounds as compared to uninfected mice. Peripheral polymorphonuclear‐dominated inflammation and larger necrosis were observed in BALB/c wounds. In conclusion, P. aeruginosa biofilm modulates wounds by suppressing central, but inducing peripheral, vascular endothelial growth factor levels and reducing host response in wounds of BALB/c mice. This suppression is detrimental to the resolution of biofilm‐infected necrosis.     

Anti-biofilm efficacy of a lactoferrin/xylitol wound hydrogel used in combination with silver wound dressings

With an epidemic increase in obesity combined with an ageing population, chronic wounds such as diabetic foot ulcers, pressure ulcers and venous leg ulcers are an increasing clinical concern. Recent studies have shown that bacterial biofilms are a major contributor to wound bioburden and interfere with the normal wound healing process; therefore, rational design of wound therapies should include analysis of anti‐biofilm characteristics. Studies using the combined treatment of bacterial biofilms with the innate immune molecule lactoferrin and the rare sugar‐alcohol xylitol have demonstrated an antimicrobial capacity against a clinical wound isolate. Studies presented here used a colony‐drip‐flow reactor biofilm model to assess the anti‐biofilm efficacy of a lactoferrin/xylitol hydrogel used in combination with commercially available silver‐based wound dressings. Log reductions in biofilm viability are compared with a commercially available wound hydrogel used in combination with the silver‐based wound dressings. For both a single species biofilm and a dual species biofilm, the lactoferrin/xylitol hydrogel in combination with the silver wound dressing Acticoat? had a statistically significant reduction in biofilm viability relative to the commercially available wound hydrogel. This study also demonstrated a statistical interaction between the lactoferrin/xylitol hydrogel and the silver wound dressing.