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.     

Influence of human acute wound fluid on the antibacterial efficacy of different antiseptic polyurethane foam dressings: An in vitro analysis

Treating infected acute and/or chronic wounds still represents a major challenge in medical care. Various interactions of antiseptic dressings with wound environments regarding antimicrobial efficacy remain unclear. Therefore, this work aimed to investigate the influence of human acute wound fluid (AWF) on the antimicrobial performance of different antiseptic foam dressings in vitro against typical bacterial wound pathogens. Eight antiseptic polyurethane foam dressings containing either a silver formulation or a polyhexamethylene‐biguanide (PHMB) were assessed regarding their antimicrobial potency against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa using a modified time‐kill assay based on ISO EN 20743. The antiseptic efficacy was evaluated standardly as well as under the influence of human AWF after 2, 4, 6, and 24 hours. The specific chemical formulation and concentration of the antiseptic substance (ionic or nanocrystalline silver, silver sulfadiazine, PHMB 0.1%/0.5%) embedded within the dressings seemed to play a key role. For certain dressings (two nanocrystalline and one ionic silver dressing), the antimicrobial efficacy was significantly reduced under the influence of AWF compared to unchallenged test series. Unchallenged the efficacy of PHMB was comparable to silver against P. aeruginosa and even significantly superior against S. aureus and E. coli. Challenged with AWF the reduction rates for silver adjusted or even exceeded (P. aeruginosa) those of PHMB. Within a challenging wound environment, especially some silver formulations demonstrated a reduced bacterial reduction. Regarding the presented in vitro results, the biomolecular interactions of antiseptic wound dressings with wound fluid should be part of more extensive investigations, considering varying factors such as bacterial species and wound (micro)environment to develop targeted therapeutic regimes for the individual.     

The efficacy of silver dressings and antibiotics on MRSA and MSSA isolated from burn patients

In this study our objectives were (1) to investigate whether meticillin‐resistant Staphylococcus aureus (MRSA) showed an increased tolerance to silver wound dressings compared with meticillin‐sensitive S. aureus (MSSA); and (2) to evaluate the effects of bacterial phenotypic states of MRSA and MSSA, and pH, on the activity of silver wound dressings and two antibiotics, ampicillin and clindamycin. Twenty MRSA strains and 10 MSSA strains isolated from burns patients in South Africa were evaluated for their susceptibility to a silver alginate and a silver carboxymethyl cellulose wound dressing, employing a corrected zone of inhibition assay, conducted on Mueller Hinton agar and a poloxamer‐based biofilm model. When exposed to the two silver dressings, all 30 S. aureus strains showed susceptibility. Possible enhanced antimicrobial efficacy of the silver dressings occurred when pH was lowered to 5.5, compared with a pH of 7.0. When all S. aureus were grown in the biofilm phenotypic state and exposed to both silver dressings and antibiotics, enhanced tolerance was noted. Susceptibility to silver was overall higher for MRSA when compared with MSSA. This study showed that the effect of pH and bacterial phenotypic state must be considered when the antimicrobial activity of silver wound dressings is being investigated. It is evident from the data generated that both pH and the bacterial phenotypic state are factors that induce changes that affect both antimicrobial performance and bacterial susceptibility.     

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.     

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.     

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.     

The antimicrobial efficacy of silver on antibiotic-resistant bacteria isolated from burn wounds

The antibiotic‐resistant bacteria are a major concern to wound care because of their ability to resist many of the antibiotics used today to treat infections. Consequently, other antimicrobials, in particular ionic silver, are considered ideal topical agents for effectively helping to manage and prevent local infections. Little is known about the antimicrobial efficacy of ionic silver on antibiotic‐resistant bacteria at different pH values. Consequently, in this study our aim was to evaluate the effect of pH on the antimicrobial efficacy of a silver alginate (SA) and a silver carboxymethyl cellulose (SCMC) dressing on antibiotic‐resistant bacteria isolated from burn patients. Forty‐nine antibiotic‐resistant bacteria, including Vancomycin‐resistant Enterococcus faecium, meticillin‐resistant Staphylococcus aureus, multidrug‐resistant (MDR) Pseudomonas aeruginosa, MDR Vibrio sp, MDR Stenotrophomonas maltophilia, extended‐spectrum ß‐lactamase (ESBL) producing Salmonella sp, ESBL producing Klebsiella pneumoniae, ESBL producing Proteus mirabilis, ESBL producing Escherichia coli and MDR Acinetobacter baumannii, routinely isolated from burn wounds were used in the study and evaluated for their susceptibility to two silver containing wound dressings using a standardised antimicrobial efficacy screening assay [corrected zone of inhibition (CZOI)]. The mean overall CZOI for the Gram‐positive isolates at a pH of 5·5 were very similar for both dressings. A mean CZOI of 5 mm was recorded for the SCMC dressing, which was slightly higher, at 5·4 mm for the SA dressing. At a pH of 7·0 both dressings, in general, showed a similar activity. However, at a pH of 8·5 the mean CZOI of the SCMC dressing was found to be significantly (P < 0·05) higher than the SA dressing for a select number of isolates. The mean overall CZOI for the Gram‐negative bacteria followed a similar pattern as observed with the Gram‐positive bacteria. Susceptibility to silver ions did vary significantly between genera and species of bacteria. Interestingly, when pH was changed from 8·5 to 5·5 antimicrobial activity for both dressings in general increased significantly (P < 0·05). Overall, all forty‐nine antibiotic‐resistant bacteria isolated from burn wounds showed susceptibility to the antimicrobial activity of both silver containing wound dressings over all pH ranges. In addition, the study showed that the performance of both dressings apparently increased when pH became more acidic. The findings in this study may help to further enhance our knowledge of the role pH plays in affecting both bacterial susceptibility and antimicrobial activity of silver containing wound dressings.     

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.     

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.     

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.     

Preclinical evaluation of a novel silver gelling fiber dressing on Pseudomonas aeruginosa in a porcine wound infection model

The wound environment is a fertile ground for biofilm forming pathogens. Once biofilms form within the wound, they can be very challenging to eradicate. The purpose of this study was to examine the effect of a gelling fiber dressing with silver using a well‐established porcine wound biofilm model. Deep partial thickness wounds were inoculated with Pseudomonas aeruginosa ATCC 27312 and covered with a polyurethane film dressing to promote biofilm formation. Wounds were then divided into treatment groups: gelling fiber dressing with silver, gelling fiber dressing without silver, hydrofiber dressing with silver, benzethonium chloride and ethylenediaminetetraacetic acid and compared to untreated control. Microbiological, biofilm, and histological wound assessments were performed on days 3, 5, and 7 postinfection. Treatment with gelling fiber dressing with silver resulted in significant reduction of P. aeruginosa biofilm when compared to all other treatment groups on every assessment time point. In addition, gelling fiber dressing with silver treatment resulted in detachment of biofilm from the wound, while wounds treated with gelling fiber dressing with and without silver showed more granulation tissue formation on day 3. Our data show that a new gelling fiber dressing with silver was effective in reducing biofilm associated P. aeruginosa in vivo. This study may have important clinical implications especially for wounds heavily colonized with gram‐negative biofilm‐forming bacteria.     

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.     

Chitin membranes containing silver nanoparticles for wound dressing application

Silver nanoparticles are gaining importance as an antimicrobial agent in wound dressings. Chitin is a biopolymer envisioned to promote rapid dermal regeneration and accelerate wound healing. This study was focused on the evaluation of chitin membranes containing silver nanoparticles for use as an antimicrobial wound dressing. Silver nanoparticles were synthesised by gamma irradiation at doses of 50 kGy in the presence of sodium alginate as stabiliser. The UV–Vis absorption spectra of nanoparticles exhibited an absorption band at 415–420 nm, which is the typical plasmon resonance band of silver nanoparticles. The peaks in the X‐ray diffraction (XRD) pattern are in agreement with the standard values of the face‐centred cubic silver. Transmission electron microscopy (TEM) images indicate silver nanoparticles with spherical morphology and small particle size in the range of 3–13 nm. In vitro antimicrobial tests were performed using Pseudomonas aeruginosa and Staphylococcus aureus to determine the antimicrobial efficiency of the chitin membranes containing 30, 50, 70 and 100 ppm nanosilver. No viable counts for P. aeruginosa were detected with 70 ppm silver nanoparticles dressing after 1‐hour exposure. A 2‐log reduction in viable cell count was observed for S. aureus after 1 hour and a 4‐log reduction after 6 hours with 100 ppm nanosilver chitin membranes. This study demonstrates the antimicrobial capability of chitin membranes containing silver nanoparticles. The chitin membranes with 100 ppm nanosilver showed promising antimicrobial activity against common wound pathogens.     

Antimicrobial efficacy of a novel silver hydrogel dressing compared to two common silver burn wound dressings: Acticoat™ and PolyMem Silver

A novel burn wound hydrogel dressing has been previously developed which is composed of 2-acrylamido-2-methylpropane sulfonic acid sodium salt with silver nanoparticles. This study compared the antimicrobial efficacy of this novel dressing to two commercially available silver dressings; Acticoat™ and PolyMem Silver^®. Three different antimicrobial tests were used: disc diffusion, broth culture, and the Live/Dead^® Baclight™ bacterial viability assay. Burn wound pathogens (P. aeruginosa, MSSA, A. baumannii and C. albicans) and antibiotic resistant strains (MRSA and VRE) were tested. All three antimicrobial tests indicated that Acticoat™ was the most effective antimicrobial agent, with inhibition zone lengths of 13.9–18.4 mm. It reduced the microbial inocula below the limit of detection (10² CFU/ml) and reduced viability by 99% within 4 h. PolyMem Silver^® had no zone of inhibition for most tested micro-organisms, and it also showed poor antimicrobial activity in the broth culture and Live/Dead^® Baclight™ assays. Alarmingly, it appeared to promote the growth of VRE. The silver hydrogel reduced most of the tested microbial inocula below the detection limit and decreased bacterial viability by 94–99% after 24 h exposure. These results support the possibility of using this novel silver hydrogel as a burn wound dressing in the future.     

Developing in vitro assays to quantitatively evaluate the interactions of dressings with wounds

Evaluating interactions between dressing and wound is important for understanding wound management. This study quantitatively compared four polyurethane foam‐based wound dressings for their absorption profile, cell penetration, and adherence using two novel in vitro assays. The dressing with uniform pore sizes varying from 25~75 μm showed the highest absorption of both culture media and serum. The same dressing showed a 1.2‐ to 3.6‐fold lower cell adherence (3 hours) than the other dressings, and ~20‐fold lower cell penetration (5 days) than dressings with pore sizes varying from 55 to 343 μm. Additionally, cell and dressing interactions using a 3‐dimensional wound healing assay showed that the dressings with the smallest pore size of 25~75 μm maintained the highest cell viability (76.3%) and promoted cell migration into the wound site. This data suggest that polyurethane foam dressing with smaller and evenly distributed pores promotes wound healing with less cellular adhesion and penetration.     

Evaluating antimicrobial efficacy of new commercially available silver dressings

Prevention and treatment of bacterial colonised/infected wounds are critical. Many commercially available silver dressings claim broad‐spectrum bactericidal activity over days and are indicated for serious conditions including burns and ulcers. However, there is no peer‐reviewed literature available for many newer dressings. This study compared the activity of some of these dressings. Six silver‐containing dressings were compared using log reduction, silver release and corrected zone of inhibition assays. Only the nanocrystalline silver dressing was bactericidal against Staphylococcus aureus, and the only other dressing that produced any log reduction was a silver collagen matrix dressing. These two dressings and a silver alginate dressing produced zones of inhibition, although the collagen matrix and alginate dressings had decreasing zone sizes over time, and the latter liquefied after five transfers. The remaining dressings (two ionic silver foam dressings and a silver sulphate dressing) did not produce zones of inhibition. For the foam, alginate and collagen matrix dressings, antimicrobial activity was related to silver release. The silver sulphate dressing released large quantities of silver, but only through the dressing edges, as the wound‐contacting surface appeared to be hydrophobic. The results of this study emphasise the importance of confirming product claims regarding silver dressing efficacy.     

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.     

Application of a drainage film reduces fibroblast ingrowth into large‐pored polyurethane foam during negative‐pressure wound therapy in an in vitro model

Negative‐pressure wound therapy (NPWT) is an advantageous treatment option in wound management to promote healing and reduce the risk of complications. NPWT is mainly carried out using open‐cell polyurethane (PU) foams that stimulate granulation tissue formation. However, growth of wound bed tissue into foam material, leading to disruption of newly formed tissue upon dressing removal, has been observed. Consequently, it would be of clinical interest to preserve the positive effects of open‐cell PU foams while avoiding cellular ingrowth. The study presented analyzed effects of NPWT using large‐pored PU foam, fine‐pored PU foam, and the combination of large‐pored foam with drainage film on human dermal fibroblasts grown in a collagen matrix. The results showed no difference between the dressings in stimulating cellular migration during NPWT. However, when NPWT was applied using a large‐pored PU foam, the fibroblasts continued to migrate into the dressing. This led to significant breaches in the cell layers upon removal of the samples after vacuum treatment. In contrast, cell migration stopped at the collagen matrix edge when fine‐pored PU foam was used, as well as with the combination of PU foam and drainage film. In conclusion, placing a drainage film between collagen matrix and the large‐pored PU foam dressing reduced the ingrowth of cells into the foam significantly. Moreover, positive effects on cellular migration were not affected, and the effect of the foam on tissue surface roughness in vitro was also reduced.     

A multimodel regime for evaluating effectiveness of antimicrobial wound care products in microbial biofilms

Microbial biofilms have become increasingly recognized as a cause of wound chronicity. There are several topical antimicrobial wound care products available for use; however, their effectiveness has routinely been demonstrated with planktonic microorganisms. There is no target reference value for antimicrobial effectiveness of wound care products in biofilm models. In addition, data on antimicrobial activity of products in biofilm models are scattered across many test methods in a variety of studies. The aim of this work is to directly compare commercial products containing the commonly used topical antimicrobial agents iodine, silver, polyhexamethylene biguanide, octenidine, hypochlorous acid, benzalkonium chloride, and a surfactant‐based topical containing poloxamer 188. Five different in vitro biofilm models of varied complexity were used, incorporating several bacterial pathogens such as Staphylococcus, Enterococcus, Streptococcus, Pseudomonas, Acinetobacter, Klebsiella, and Enterobacter. The fungal pathogens Candida albicans and Candida auris were also evaluated. A multispecies bacterial biofilm model was also used to evaluate the products. Additionally, C. albicans was used in combination with S. aureus and P. aeruginosa in a multikingdom version of the polymicrobial biofilm model. Statistically significant differences in antimicrobial performance were observed between treatments in each model and changing microbial growth conditions or combinations of organisms resulted in significant performance differences for some treatments. The iodine and benzalkonium chloride‐containing products were overall the most effective in vitro and were then selected for in vivo evaluation in an infected immunocompromised murine model. Unexpectedly, the iodine product was statistically (P > .05) no different than the untreated control, while the benzalkonium chloride containing product significantly (P < .05) reduced the biofilm compared to untreated control. This body of work demonstrates the importance of not only evaluating antimicrobial wound care products in biofilm models but also the importance of using several different models to gain a comprehensive understanding of products' effectiveness.