Antimicrobial dressing efficacy against mature Pseudomonas aeruginosa biofilm on porcine skin explants

Biofilm Formation by Lactobacillus Strains of Modern Probiotics and Their Antagonistic Activity against Opportunistic Bacteria

The species identity of the studied lactobacillus strains was confirmed by matrix-activated laser desorption/ionization with time-of-flight ion separation (MALDI-TOF mass spectrometry). Lactobacillus strains differed in the dynamics of lactic acid accumulation and changes in the pH of the culture medium. The culture medium affected adhesion ability of lactobacilli. The ability to adhere does not affect the formation of biofilms by lactobacillus strains except for the L. acidophilus La5 strain, which has low adhesion ability and fewer microbial cells detected after mechanical destruction of the biofilm. The metabiotics of the lactobacillus culture medium have an antagonistic effect on conditionally pathogenic microorganisms. Adhesion, biofilm formation, and antagonistic activity of probiotic lactobacillus strains are strain-specific properties.

Impact of continuous topical oxygen therapy on biofilm gene expression in a porcine tissue model

OBJECTIVE

The effect of continuous topical oxygen therapy (cTOT) on Pseudomonas aeruginosa biofilm gene transcription profiles following inoculation onto porcine skin, using a customised molecular assay was determined.

METHOD

Sterilised porcine skin explants were inoculated with Pseudomonas aeruginosa in triplicate: 0 hours as negative control; 24 hours cTOT device on; 24 hours cTOT device off. The oxygen delivery system of the cTOT device was applied to the inoculated tissue and covered with a semi-occlusive dressing. All samples were incubated at 37±2°C for 24 hours, with the 0 hours negative control inoculated porcine skin samples recovered immediately. Planktonic suspensions and porcine skin biopsy samples were taken at 0 hours and 24 hours. Samples were processed and quantifiably assessed using gene specific reverse transcription-quantitative polymerase chain reaction assays for a panel of eight Pseudomonas aeruginosa genes (16S, pelA, pslA, rsaL, pcrV, pscQ, acpP, cbrA) associated with biofilm formation, quorum sensing, protein secretion/translocation and metabolism.

RESULTS

Transcriptional upregulation of pelA, pcrV and acpP, responsible for intracellular adhesion, needletip protein production for type-3 secretion systems and fatty acid synthesis during proliferation, respectively, was observed when the cTOT device was switched on compared to when the device was switched off. Data suggest increased metabolic activity within bacterial cells following cTOT treatment.

CONCLUSION

cTOT is an adjunctive therapy that supports faster healing and pain reduction in non-healing hypoxic wounds. Oxygen has previously been shown to increase susceptibility of biofilms to antibiotics through enhancing metabolism. Observed gene expression changes highlighted the impact of cTOT on biofilms, potentially influencing antimicrobial treatment success in wounds. Further in vitro and clinical investigations are warranted.

Antiviral Activity of Ag5IO6, a Unique Silver Compound

Pentasilver hexaoxoiodate (Ag5IO6) has broad-spectrum antimicrobial efficacy, including the long-term prevention of microbial adherence, the rapid killing of planktonic microorganisms, and the elimination of mature biofilms. This study's goal was to determine whether it may also have antiviral activity against structurally distinct viruses. Ag5IO6 was tested following ASTM E1052-20, Standard Practice to Assess the Activity of Microbicides Against Viruses in Suspension, against adenovirus type 5, murine norovirus, poliovirus type 1, SARS-CoV-2 (original), and SARS-CoV-2 (omicron) (host cells: H1HeLa, RAW 264.7, LLC-MK2, Vero E6, and Vero E6, respectively). A 0.1 g/mL Ag5IO6 suspension was prepared and the viruses were exposed for 30 min, 4 h, or 24 h. Exposure to Ag5IO6 resulted in complete kill of SARS-CoV-2 (omicron) within 30 min, as well as complete kill of both SARS-CoV-2 (original) and the murine norovirus within 4 h. Ag5IO6 showed increasing activity over time against the adenovirus, but did not achieve a 3-log reduction within 24 h, and showed no antiviral activity against the poliovirus. These results demonstrate that Ag5IO6 has antiviral activity against medically important viruses, in addition to its well-characterized antimicrobial activity, suggesting that it may be valuable in situations where the prevention or simultaneous treatment of microbes and viruses are necessary.

A neoteric antibacterial ceria-silver nanozyme for abiotic surfaces

Community-associated and hospital-acquired infections caused by bacteria continue to yield major global challenges to human health. Bacterial contamination on abiotic surfaces is largely spread via high-touch surfaces and contemporary standard disinfection practices show limited efficacy, resulting in unsatisfactory therapeutic outcomes. New strategies that offer non-specific and broad protection are urgently needed. Herein, we report our novel ceria-silver nanozyme engineered at a molar ratio of 5:1 and with a higher trivalent (Ce3+) surface fraction. Our results reveal potent levels of surface catalytic activity on both wet and dry surfaces, with rapid, and complete eradication of Pseudomonas aeruginosa, Staphylococcus aureus, and methicillin resistant S. aureus, in both planktonic and biofilm form. Preferential electrostatic adherence of anionic bacteria to the cationic nanozyme surface leads to a catastrophic loss in both aerobic and anaerobic respiration, DNA damage, osmodysregulation, and finally, programmed bacterial lysis. Our data reveal several unique mechanistic avenues of synergistic ceria-Ag efficacy. Ag potentially increases the presence of Ce3+ sites at the ceria-Ag interface, thereby facilitating the formation of harmful H2O2, followed by likely permeation across the cell wall. Further, a weakened Ag-induced Ce-O bond may drive electron transfer from the Ec band to O2, thereby further facilitating the selective reduction of O2 toward H2O2 formation. Ag destabilizes the surface adsorption of molecular H2O2, potentially leading to higher concentrations of free H2O2 adjacent to bacteria. To this end, our results show that H2O2 and/or NO/NO2-/NO3- are the key liberators of antibacterial activity, with a limited immediate role being offered by nanozyme-induced ROS including O2•- and OH•, and likely other light-activated radicals. A mini-pilot proof-of-concept study performed in a pediatric dental clinic setting confirms residual, and continual nanozyme antibacterial efficacy over a 28-day period. These findings open a new approach to alleviate infections caused by bacteria for use on high-touch hard surfaces.

Protium spruceanum Extract Enhances Mupirocin Activity When Combined with Nanoemulsion-Based Hydrogel: A Multi-Target Strategy for Treating Skin and Soft Tissue Infections

The treatment of skin and soft tissue infections (SSTIs) can be challenging due to bacterial resistance, particularly from strains like MRSA and biofilm formation. However, combining conventional antibiotics with natural products shows promise in treating SSTIs. The objective of this study is to develop a nanoemulsion-based hydrogel containing Protium spruceanum extract and mupirocin and evaluate its potential for the treatment of SSTIs. The nanoemulsion was obtained by phase inversion and subsequently characterized. The antibacterial activity was evaluated in vitro against S. aureus MRSA, including the synergism of the combination, changes in membrane permeability using flow cytometry, and the anti-biofilm effect. In addition, the irritative potential was evaluated by the HET-CAM assay. The combination exhibited synergistic antibacterial activity against S. aureus and MRSA due to the extract enhancing membrane permeability. The hydrogel demonstrated suitable physicochemical properties, inhibited biofilm formation, and exhibited low irritation. The formulation was nanometric (176.0 ± 1.656 nm) and monodisperse (polydispersity index 0.286 ± 0.011). It exhibited a controlled release profile at 48 h and high encapsulation efficacy (94.29 ± 4.54% for quercitrin and 94.20 ± 5.44% for mupirocin). Therefore, these findings suggest that the hydrogel developed could be a safe and effective option for treating SSTIs.

Bioactive Dressing: A New Algorithm in Wound Healing

Wound management presents a significant global challenge, necessitating a comprehensive understanding of wound care products and clinical expertise in selecting dressings. Bioactive dressings (BD) represent a diverse category of dressings, capable of influencing wound healing through various mechanisms. These dressings, including honey, hyaluronic acid, collagen, alginates, and polymers enriched with polyhexamethylene biguanide, chitin, and chitosan derivatives, create a conducive environment for healing, promoting moisture balance, pH regulation, oxygen permeability, and fluid management. Interactive dressings further enhance targeted action by serving as substrates for bioactive agents. The continuous evolution of BDs, with new products introduced annually, underscores the need for updated knowledge in wound care. To facilitate dressing selection, a practical algorithm considers wound exudate, infection probability, and bleeding, guiding clinicians through the process. This algorithm aims to optimize wound care by ensuring the appropriate selection of BDs tailored to individual patient needs, ultimately improving outcomes in wound management.

A surfactant-based dressing can reduce the appearance of Pseudomonas aeruginosa pigments and uncover the dermal extracellular matrix in an ex vivo porcine skin wound model

From previous studies, we have shown that viable colony forming units of bacteria and bacterial biofilms are reduced after sequential treatment with a surfactant-based dressing. Here, we sought to test the impact on visible bacterial pigments and the ultrastructural impact following the sequential treatment of the same surfactant-based dressing. Mature Pseudomonas aeruginosa biofilms were grown on ex vivo porcine skin explants, and an imaging-based analysis was used to compare the skin with and without a concentrated surfactant. In explants naturally tinted by bacterial chromophores, wiping alone had no effect, while the use of a surfactant-based dressing reduced coloration. Similarly, daily wiping led to increased immunohistochemical staining for P. aeruginosa antigens, but not in the surfactant group. Confocal immunofluorescent imaging revealed limited bacterial penetration and coating of the dermis and loose pieces of sloughing material. Ultrastructural analysis confirmed that the biofilms were masking the extracellular matrix (ECM), but the surfactant could remove them, re-exposing the ECM. The masking of the ECM may provide another non-inflammatory explanation for delayed healing, as the ECM is no longer accessible for wound cell locomotion. The use of a poloxamer-based surfactant appears to be an effective way to remove bacterial chromophores and the biofilm coating the ECM fibres.

Bacterial Biofilm in Chronic Wounds and Possible Therapeutic Approaches

Wound repair and skin regeneration is a very complex orchestrated process that is generally composed of four phases: hemostasis, inflammation, proliferation, and remodeling. Each phase involves the activation of different cells and the production of various cytokines, chemokines, and other inflammatory mediators affecting the immune response. The microbial skin composition plays an important role in wound healing. Indeed, skin commensals are essential in the maintenance of the epidermal barrier function, regulation of the host immune response, and protection from invading pathogenic microorganisms. Chronic wounds are common and are considered a major public health problem due to their difficult-to-treat features and their frequent association with challenging chronic infections. These infections can be very tough to manage due to the ability of some bacteria to produce multicellular structures encapsulated into a matrix called biofilms. The bacterial species contained in the biofilm are often different, as is their capability to influence the healing of chronic wounds. Biofilms are, in fact, often tolerant and resistant to antibiotics and antiseptics, leading to the failure of treatment. For these reasons, biofilms impede appropriate treatment and, consequently, prolong the wound healing period. Hence, there is an urgent necessity to deepen the knowledge of the pathophysiology of delayed wound healing and to develop more effective therapeutic approaches able to restore tissue damage. This work covers the wound-healing process and the pathogenesis of chronic wounds infected by biofilm-forming pathogens. An overview of the strategies to counteract biofilm formation or to destroy existing biofilms is also provided.

Assessment of antibiotic release and antibacterial efficacy from pendant glutathione hydrogels using ex vivo porcine skin

Acute bacterial skin and skin structure infections (ABSSSIs) confer a substantial burden on the healthcare system. Local antibiotic delivery systems can provide controlled drug release directly to the site of infection to maximize efficacy and minimize systemic toxicity. The purpose of this study was to examine the antibacterial activity of antibiotic-loaded glutathione-conjugated poly(ethylene glycol) hydrogels (GSH-PEG) against ABSSSIs utilizing an ex vivo porcine dermal explant model. Vancomycin- or meropenem-loaded GSH-PEG hydrogels at 3 different dose levels were loaded over 1 h. Drug release was monitored in vitro under submerged conditions, by the Franz cell diffusion method, and ex vivo utilizing a porcine dermis model. Antibacterial activity was assessed ex vivo on porcine dermis explants inoculated with Staphylococcus aureus or Pseudomonas aeruginosa isolates treated with vancomycin- or meropenem-loaded GSH-PEG hydrogels, respectively. Histological assessment of the explants was conducted to evaluate tissue integrity and viability in the context of the experimental conditions. A dose-dependent release was observed from vancomycin and meropenem hydrogels, with in vitro Franz cell diffusion data closely representing ex vivo vancomycin release, but not high dose meropenem release. High dose vancomycin-loaded hydrogels resulted in a >3 log10 clearance against all S. aureus isolates at 48 h. High dose meropenem-loaded hydrogels achieved 6.5, 4, and 2 log10 reductions in CFU/ml against susceptible, intermediate, and resistant P. aeruginosa isolates, respectively. Our findings demonstrate the potential application of GSH-PEG hydrogels for flexible, local antibiotic delivery against bacterial skin infections.

In vitro prevention and inactivation of biofilms using controlled-release iodine foam dressings for wound healing

Microbial biofilms are a major hindrance in the wound healing process, prolonging the inflammatory response phase, thus making them a target in treatment. The aim of this study is to assess the antibacterial properties of commercially available wound dressings, of various material composition and antibacterial agents, towards multiple in vitro microbial and biofilm models. A variety of in vitro microbial and biofilm models were utilised to evaluate the ability of wound dressing materials to sequester microbes, prevent dissemination and manage bioburden. Sequestering and dissemination models were used to evaluate the ability of wound dressing materials to prevent the biofilm-forming bacterium, Pseudomonas aeruginosa, from migrating through dressing materials over a 24-72 h challenge period. Additionally, Centre for Disease Control (CDC) Bioreactor and Drip Flow models were used to evaluate antibacterial killing efficacy towards established P. aeruginosa and Staphylococcus aureus biofilms using more challenging, wound-like models. Controlled-release iodine foam and silver-impregnated carboxymethylcellulose (CMC) wound dressing materials demonstrated potent biofilm management properties in comparison to a methylene blue and gentian violet-containing foam dressing. Both the iodine-containing foam and silver-impregnated CMC materials effectively prevented viable P. aeruginosa dissemination for up to 72 h. In addition, the controlled-release iodine foam and silver-impregnated CMC materials reduced P. aeruginosa bioburden in the Drip Flow model. The controlled-release iodine foam demonstrated superiority in the CDC Bioreactor model, as both the silver- and iodine-containing materials reduced S. aureus to the limit of detection, but P. aeruginosa growth was only completely reduced by controlled-release iodine foam dressing materials. The data generated within the in vitro biofilm models supports the clinical data available in the public domain for the implementation of iodine foam dressings for effective biofilm management and control in wound care.

Real-time in vivo monitoring of the antimicrobial action of combination therapies in the management of infected topical wounds

The increasing prevalence of non-healing infected wounds has become a serious concern in the clinical practice, being associated to population aging and to the rising prevalence of several chronic conditions such as diabetes. Herein, the evaluation of the bactericidal and antibiofilm effects of the natural antiseptic terpenes thymol and farnesol standing alone or in combination with the standard care antiseptic chlorhexidine was carried out both in vitro and in vivo. The in vitro combinatorial treatment of chlorhexidine associated with those terpenes against Staphylococcus aureus in its planktonic and sessile forms demonstrated a superior antibacterial activity than that of chlorhexidine alone. Real-time in vivo monitoring of infection progression and antimicrobial treatment outcomes were evaluated using the bioluminescent S. aureus strain Xen36. In vivo studies on infected wound splinting murine models corroborated the superior bactericidal effects of the combinatorial treatments here proposed. Moreover, the encapsulation of thymol in electrospun Eudragit® S100 (i.e., a synthetic anionic copolymer of methacrylic acid and ethyl acrylate)-based wound dressings was also carried out in order to design efficient antimicrobial wound dressings.

Antimicrobial Natural Hydrogels in Biomedicine: Properties, Applications, and Challenges-A Concise Review

Natural hydrogels are widely used as biomedical materials in many areas, including drug delivery, tissue scaffolds, and particularly wound dressings, where they can act as an antimicrobial factor lowering the risk of microbial infections, which are serious health problems, especially with respect to wound healing. In this review article, a number of promising strategies in the development of hydrogels with biocidal properties, particularly those originating from natural polymers, are briefly summarized and concisely discussed. Common strategies to design and fabricate hydrogels with intrinsic or stimuli-triggered antibacterial activity are exemplified, and the mechanisms lying behind these properties are also discussed. Finally, practical antibacterial applications are also considered while discussing the current challenges and perspectives.

Activity of a hypochlorous acid-producing electrochemical bandage as assessed with a porcine explant biofilm model

The activity of a hypochlorous acid-producing electrochemical bandage (e-bandage) in preventing methicillin-resistant Staphylococcus aureus infection (MRSA) infection and removing biofilms formed by MRSA was assessed using a porcine explant biofilm model. e-Bandages inhibited S. aureus infection (p = 0.029) after 12 h (h) of exposure and reduced 3-day biofilm viable cell counts after 6, 12, and 24 h exposures (p = 0.029). Needle-type microelectrodes were used to assess HOCl concentrations in explant tissue as a result of e-bandage treatment; toxicity associated with e-bandage treatment was evaluated. HOCl concentrations in infected and uninfected explant tissue varied between 30 and 80 µM, decreasing with increasing distance from the e-bandage. Eukaryotic cell viability was reduced by an average of 71% and 65% in fresh and day 3-old explants, respectively, when compared to explants exposed to nonpolarized e-bandages. HOCl e-bandages are a promising technology that can be further developed as an antibiotic-free treatment for wound biofilm infections.

Benefits of Manuka Honey in the Management of Infectious Diseases: Recent Advances and Prospects

The benefits of honey have been recognized since ancient times for treating numerous diseases. However, in today's modern era, the use of traditional remedies has been rapidly diminishing due to the complexities of modern lifestyles. While antibiotics are commonly used and effective in treating pathogenic infections, their inappropriate use can lead to the development of resistance among microorganisms, resulting in their widespread prevalence. Therefore, new approaches are constantly required to combat drug-resistant microorganisms, and one practical and useful approach is the use of drug combination treatments. Manuka honey, derived from the manuka tree (Leptospermum scoparium) found exclusively in New Zealand, has garnered significant attention for its biological potential, particularly due to its antioxidant and antimicrobial properties. Moreover, when combined with antibiotics, it has demonstrated the ability to enhance their effectiveness. In this review, we delve into the chemical markers of manuka honey that are currently known, as well as detail the impact of manuka honey on the management of infectious diseases up to the present.

Efficacy and toxicity of hydrogen peroxide producing electrochemical bandages in a porcine explant biofilm model

AIMS

Effects of H₂ O₂ producing electrochemical-bandages (e-bandages) on methicillin-resistant Staphylococcus aureus colonization and biofilm removal were assessed using a porcine explant biofilm model. Transport of H₂ O₂ produced from the e-bandage into explant tissue and associated potential toxicity were evaluated.

METHODS AND RESULTS

Viable prokaryotic cells from infected explants were quantified after 48 h treatment with e-bandages in three ex vivo S. aureus infection models: (1) reducing colonization, (2) removing young biofilms and (3) removing mature biofilms. H₂ O₂ concentration-depth profiles in explants/biofilms were measured using microelectrodes. Reductions in eukaryotic cell viability of polarized and nonpolarized noninfected explants were compared. e-Bandages effectively reduced S. aureus colonization (p = 0.029) and reduced the viable prokaryotic cell concentrations of young biofilms (p = 0.029) with limited effects on mature biofilms (p > 0.1). H₂ O₂ penetrated biofilms and explants and reduced eukaryotic cell viability by 32-44% compared to nonpolarized explants.

CONCLUSIONS

H₂ O₂ producing e-bandages were most active when used to reduce colonization and remove young biofilms rather than to remove mature biofilms.

SIGNIFICANCE AND IMPACT OF STUDY

The described e-bandages reduced S. aureus colonization and young S. aureus biofilms in a porcine explant wound model, supporting their further development as an antibiotic-free alternative for managing biofilm infections.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Challenges in the diagnosis and management of wound infection

Human epithelia are constantly exposed to microorganisms present in the environment or residing as part of commensal flora. Despite this exposure, infections involving the skin and subcutaneous tissue in healthy individuals are, fortunately, quite rare. Many of the wounds that afflict the human body occur in individuals of ill health and/or where the mechanism of wounding is impeded by host immunological, physiological or regenerative dysfunction. The interplay between microorganisms and host immunity is complex and remains ill defined; however, the interpretation of downstream manifestations of the host response to invading microorganisms is still based largely on the clinical signs and symptoms of an active infectious process. In this review article we will provide a brief overview of the current challenges clinicians face in diagnosing wound infections, how chronic infections caused by biofilms are a major challenge, and how there have been minimal advancements in developing new diagnostics or therapeutics in the identification and management of wound infections.

Implications of endotoxins in wound healing: a narrative review

Bacterial toxins are thought to play a role in delayed wound healing in critically colonised and infected wounds. Endotoxins are released from Gram-negative bacteria when they are lysed by host phagocytic cells during an immune response, or by antimicrobial agents, potentially leading to a detrimental effect on the host tissues. Endotoxins can affect all aspects of the wound healing process, leading to delayed healing and contributing to wound chronicity. Release of endotoxins by bacteria can also have serious systemic effects (for example, septic shock) that can lead to high levels of patient mortality. This review summarises the role and implications on wound healing of bacterial endotoxins, describing the impact of endotoxins on the various phases of the wound healing response. There is a paucity of in vivo/clinical evidence linking endotoxins attributed to a wound (via antibiotic treatment) or their release from infecting bacteria with parameters of delayed wound healing. Future work should investigate if this link is apparent and determine the mechanism(s) by which such detrimental effects occur, offering an opportunity to identify possible treatment pathways. This paper describes the phenomenon of antimicrobial-induced endotoxin release and summarises the use of wound dressings to reduce wound bioburden without inducing microbial death and subsequent release of endotoxins, thus limiting their detrimental effects.

Effect of Nanosulfur Against Multidrug-Resistant Staphylococcus pseudintermedius and Pseudomonas aeruginosa

Multidrug resistance (MDR) has significantly increased in the past decades and the use of nanotechnology has opened new venues for novel treatments. Nanosulfur is a potent antimicrobial agent and a cheaper alternative to other nanomaterials. However, very few studies have been published on its activity against MDR organisms. Therefore, the goal of this in vitro study was to assess cytotoxicity, antimicrobial, and anti-biofilm activity of nanosulfur (47 nm, orthorhombic) against clinical isolates of MDR Staphylococcus pseudintermedius (SP) and Pseudomonas aeruginosa (PA) in planktonic and biofilm state using canine skin explants. Nanosilver (50 nm, spherical) was tested as a comparative control. Concentrations between 1866.7 and 0.11 μg/mL of both nanoparticles were tested. The ultrastructure of nanosulfur was assessed via electron microscopy. Both types of nanoparticles showed no direct cytotoxicity on a canine keratinocyte cell line. In the planktonic phase, nanosulfur was able to inhibit or kill (6-log₁₀ reduction of CFU) 7 of 10 MDR-SP isolates at 233.3 μg/mL, whereas, when in biofilm state, 6 of 10 isolates were killed at different concentrations (233.33 to 1866.7 μg/mL). Nanosilver did not show any antimicrobial or anti-biofilm activity at any concentrations tested. Both types of nanoparticles were ineffective against MDR-PA in either state. Ultrastructurally, nanosulfur was present in individual nanoparticles as well as forming larger nanoclusters. This is the first study showing an antimicrobial and anti-biofilm activity of nanosulfur for MDR-SP in absence of cytotoxicity. Nanosulfur has the potential to be used in veterinary and human medicine as effective, safe, and cheap alternative to antimicrobials and anti-biofilm agents currently available. KEY POINTS: • Nanosulfur is a better alternative than nanosilver to treat MDR-Staphylococci. • Nanosulfur is an effective agent against MDR-Staphyloccocal biofilm. • Canine skin explant model is reliable for testing anti-biofilm agents.

Controlled-release iodine foam dressings demonstrate broad-spectrum biofilm management in several in vitro models

Multiple in vitro models were utilised to evaluate the biofilm management capabilities of seven commercially-available wound dressings, varying in composition and antibacterial ingredients, to reduce common aerobic, anaerobic, and multispecies biofilms. The Center for Disease Control bioreactor was used to evaluate single species Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) 24 and 48 hours biofilms, as well as a multispecies biofilm consisting of these two organisms in addition to Enterococcus faecalis (E. faecalis). As wound biofilms often exist in hypoxic wound environments, a direct contact anaerobic model system was used to evaluate efficacy on Bacteroides fragilis (B. fragilis). Biofilm control was evaluated against P. aeruginosa in the drip flow bioreactor model, where a constant flow of proteinaceous media is used to create a more challenging and wound-like model. The results demonstrated that biofilm management capabilities varied amongst wound dressings. Two dressings, a controlled-release iodine foam dressing and a silver nanocrystalline dressing, showed potent >4 log reductions in recovered organisms compared with untreated controls in all biofilm models evaluated. The effectiveness of other dressings to manage bioburden varied between dressing, test organism, and model system. A silver foam dressing showed moderate biofilm control in some models. However, biofilm exposure to methylene blue and gentian violet-containing foam dressings showed negligible log reductions in all in vitro biofilm methods examined. The data outlined in this in vitro study support the use of the iodine foam dressing for wounds with infection and biofilm.

Biofilm Management in Wound Care

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the basics of biofilm infection and be able to distinguish between planktonic and biofilm modes of growth. 2. Have a working knowledge of conventional and emerging antibiofilm therapies and their modes of action as they pertain to wound care. 3. Understand the challenges associated with testing and marketing antibiofilm strategies and the context within which these strategies may have effective value.

SUMMARY

The Centers for Disease Control and Prevention estimate for human infectious diseases caused by bacteria with a biofilm phenotype is 65 percent and the National Institutes of Health estimate is closer to 80 percent. Biofilms are hostile microbial aggregates because, within their polymeric matrix cocoons, they are protected from antimicrobial therapy and attack from host defenses. Biofilm-infected wounds, even when closed, show functional deficits such as deficient extracellular matrix and impaired barrier function, which are likely to cause wound recidivism. The management of invasive wound infection often includes systemic antimicrobial therapy in combination with débridement of wounds to a healthy tissue bed as determined by the surgeon who has no way of visualizing the biofilm. The exceedingly high incidence of false-negative cultures for bacteria in a biofilm state leads to missed diagnoses of wound infection. The use of topical and parenteral antimicrobial therapy without wound débridement have had limited impact on decreasing biofilm infection, which remains a major problem in wound care. Current claims to manage wound biofilm infection rest on limited early-stage data. In most cases, such data originate from limited experimental systems that lack host immune defense. In making decisions on the choice of commercial products to manage wound biofilm infection, it is important to critically appreciate the mechanism of action and significance of the relevant experimental system. In this work, the authors critically review different categories of antibiofilm products, with emphasis on their strengths and limitations as evident from the published literature.

In vitro Activity of Antimicrobial Wound Dressings on P. aeruginosa Wound Biofilm

The treatment of acute and chronic infected wounds with residing biofilm still poses a major challenge in medical care. Interactions of antimicrobial dressings with bacterial load, biofilm matrix and the overall protein-rich wound microenvironment remain insufficiently studied. This analysis aimed to extend the investigation on the efficacy of a variety of antimicrobial dressings using an in vitro biofilm model (lhBIOM) mimicking the specific biofilm-environment in human wounds. Four wound dressings containing polyhexanide (PHMB), octendine di-hydrochloride (OCT), cadexomer-iodine (C-IOD) or ionic silver (AG) were compared regarding their antimicrobial efficacy. Quantitative analysis was performed using a quantitative suspension method, separately assessing remaining microbial counts within the solid biofilm as well as the dressing eluate (representing the absorbed wound exudate). Dressing performance was tested against P. aeruginosa biofilms over the course of 6 days. Scanning electron microscopy (SEM) was used to obtain qualitative visualization on changes in biofilm structure. C-IOD demonstrated superior bacterial reduction. In comparison it was the only dressing achieving a significant reduction of more than 7 log₁₀ steps within 3 days. Neither the OCT- nor the AG-containing dressing exerted a distinct and sustained antimicrobial effect. PHMB achieved a non-significant microbicidal effect (1.71 ± 0.31 log₁₀ steps) at day 1. Over the remaining course (6 days) it demonstrated a significant microbistatic effect compared to OCT, AG and the control. Quantitative results in the dressing eluate correlate with those of the solid biofilm model. Overall, AG- and OCT-containing dressings did not achieve the expected anti-biofilm efficacy, while C-IOD performed best. Chemical interaction with the biofilms extrapolymeric substance (EPS), visualized in the SEM, and dressing configuration (agent concentration and release pattern) are suspected to be responsible. The unexpected low and diverse results of the tested antimicrobial dressings indicate a necessity to rethink non-debridement anti-biofilm therapy. Focussing on the combination of biofilm-disruptive (for EPS structure) and antimicrobial (for residing microorganisms) features, as with C-IOD, using dehydration and iodine, appears reasonably complementary and an optimal solution, as suggested by the here presented in vitro data.

Development of an Experimental Ex Vivo Wound Model to Evaluate Antimicrobial Efficacy of Topical Formulations

Wound infections are considered a major cause for wound-associated morbidity. There is a high demand for alternative, robust, and affordable methods that can provide relatable and reproducible results when testing topical treatments, both in research and in the pharmaceutical industry. Here we present an ex vivo wound infection model using porcine skin and a burn wounding method, allowing for the efficacy evaluation of topical antimicrobial formulations. Utilizing this model, we demonstrate the potential of topical treatments after infecting the wounds with clinically significant bacteria, P. aeruginosa and S. aureus. We show that the method is compatible with several analytical tools used to analyze infection and antimicrobial effects. Both bacterial strains successfully infected the wound surface, as well as deeper regions of the tissue. Quantification of viable bacteria on the wound surface and in the tissue, longitudinal measurements of bioluminescence, fluorescence microscopy, and scanning electron microscopy were used to confirm the effects of antibacterial treatments. Furthermore, we show that biofilms are formed on the wound surface, indicating that the demonstrated method mirrors typical in vivo infections.

In Vitro Efficacy of Bacterial Cellulose Dressings Chemisorbed with Antiseptics against Biofilm Formed by Pathogens Isolated from Chronic Wounds

Local administration of antiseptics is required to prevent and fight against biofilm-based infections of chronic wounds. One of the methods used for delivering antiseptics to infected wounds is the application of dressings chemisorbed with antimicrobials. Dressings made of bacterial cellulose (BC) display several features, making them suitable for such a purpose. This work aimed to compare the activity of commonly used antiseptic molecules: octenidine, polyhexanide, povidone-iodine, chlorhexidine, ethacridine lactate, and hypochlorous solutions and to evaluate their usefulness as active substances of BC dressings against 48 bacterial strains (8 species) and 6 yeast strains (1 species). A silver dressing was applied as a control material of proven antimicrobial activity. The methodology applied included the assessment of minimal inhibitory concentrations (MIC) and minimal biofilm eradication concentration (MBEC), the modified disc-diffusion method, and the modified antibiofilm dressing activity measurement (A.D.A.M.) method. While in 96-well plate-based methods (MIC and MBEC assessment), the highest antimicrobial activity was recorded for chlorhexidine, in the modified disc-diffusion method and in the modified A.D.A.M test, povidone-iodine performed the best. In an in vitro setting simulating chronic wound conditions, BC dressings chemisorbed with polyhexanide, octenidine, or povidone-iodine displayed a similar or even higher antibiofilm activity than the control dressing containing silver molecules. If translated into clinical conditions, the obtained results suggest high applicability of BC dressings chemisorbed with antiseptics to eradicate biofilm from chronic wounds.

Comparative analysis of biofilm models to determine the efficacy of antimicrobials

Biofilms are one of the greatest challenges in today's treatment of chronic wounds. While antimicrobials kill platonic bacteria within seconds, they are rarely able to harm biofilms. In order to identify effective substances for antibacterial therapy, cost-efficient, standardized and reproducible models that aim to mimic the clinical situation are required. In this study, two 3D biofilm models based on human plasma with immune cells (lhBIOM) or based on sheep blood (sbBIOM) containing S. aureus or P. aeruginosa, are compared with the human biofilm model hpBIOM regarding their microscopic structure (scanning electron microscopy; SEM) and their bacterial resistance to octenidine hydrochloride (OCT) and a sodium hypochlorite (NaOCl) wound-irrigation solution. The three analyzed biofilm models show little to no reaction to treatment with the hypochlorous solution while planktonic S. aureus and P. aeruginosa cells are reduced within minutes. After 48 h, octenidine hydrochloride manages to erode the biofilm matrix and significantly reduce the bacterial load. The determined effects are qualitatively reflected by SEM. Our results show that both ethically acceptable human and sheep blood based biofilm models can be used as a standard for in vitro testing of new antimicrobial substances. Due to their composition, both fulfill the criteria of a reality-reflecting model and therefore should be used in the approval for new antimicrobial agents.

Antimicrobial stewardship of antiseptics that are pertinent to wounds: the need for a united approach

Long before the nature of infection was recognized, or the significance of biofilms in delayed healing was understood, antimicrobial agents were being used in wound care. In the last 70 years, antibiotics have provided an effective means to control wound infection, but the continued emergence of antibiotic-resistant strains and the documented antibiotic tolerance of biofilms has reduced their effectiveness. A range of wound dressings containing an antimicrobial (antibiotic or non-antibiotic compound) has been developed. Whereas standardized methods for determining the efficacy of non-antibiotic antimicrobials in bacterial suspension tests were developed in the early twentieth century, standardized ways of evaluating the efficacy of antimicrobial dressings against microbial suspensions and biofilms are not available. Resistance to non-antibiotic antimicrobials and cross-resistance with antibiotics has been reported, but consensus on breakpoints is absent and surveillance is impossible. Antimicrobial stewardship is therefore in jeopardy. This review highlights these difficulties and in particular the efficacy of current non-antibiotic antimicrobials used in dressings, their efficacy, and the challenges of translating in vitro efficacy data to the efficacy of dressings in patients. This review calls for a unified approach to developing standardized methods of evaluating antimicrobial dressings that will provide an improved basis for practitioners to make informed choices in wound care.

Efficacy of topical cadexomer iodine treatment in chronic wounds: Systematic review and meta-analysis of comparative clinical trials

The aim of this study was to summarise the clinical evidence supporting almost 40 years of topical cadexomer iodine (CIOD) use in wound bed preparation by removing barriers to healing such as exudate, slough, bioburden, and infection and allowing chronic wound progression. A systematic review was conducted (Embase/PubMed, November 2020) to identify relevant comparative studies meeting inclusion criteria. Meta‐analyses were performed using a fixed‐effects (I² < 50%) or random‐effects model (I² ≥ 50%) depending on statistical heterogeneity. Dichotomous outcomes were reported as relative risk (RR) and continuous outcomes as mean difference (MD), with 95% confidence intervals. In total, 436 publications were identified of which 13 were comparative trials including outcomes of interest. Significant reductions in exudate, pus/debris, slough, bioburden, and infection were reported in chronic wounds treated with CIOD, compared with standard of care (SOC). Meta‐analyses highlighted the positive impact of CIOD on mean wound area reduction (MD = 2.35 cm², 95% CI = 0.34–4.36, P = .0219) after eight weeks treatment and overall wound healing events compared to SOC; wounds including venous leg ulcers, diabetic foot ulcers, and pressure ulcers treated with CIOD were more than twice as likely to heal than those receiving SOC (RR = 2.30, 95% CI = 1.54–3.45, P < .0001). This meta‐analysis demonstrates the efficacy of CIOD on chronic wounds through removal of barriers to healing. CIOD should be considered in wound bed preparation and treatment protocols.

Mini-review: from in vitro to ex vivo studies: an overview of alternative methods for the study of medical biofilms

Microbial biofilms are a natural adaptation of microorganisms, typically composed of multiple microbial species, exhibiting complex community organization and cooperation. Biofilm dynamics and their complex architecture are challenging for basic analyses, including the number of viable cells, biomass accumulation, biofilm morphology, among others. The methods used to study biofilms range from in vitro techniques to complex in vivo models. However, animal welfare has become a major concern, not only in society, but also in the academic and scientific field. Thus, the pursuit for alternatives to in vivo biofilm analyses presenting characteristics that mimic in vivo conditions has become essential. In this context, the present review proposes to provide an overview of strategies to study biofilms of medical interest, with emphasis on alternatives that approximate experimental conditions to host-associated environments, such as the use of medical devices as substrata for biofilm formation, microcosm and ex vivo models.

A review of iodine-based compounds, with a focus on biofilms: results of an expert panel

Biofilms play a central role in the chronicity of non-healing lesions such as venous leg ulcers and diabetic foot ulcers. Therefore, biofilm management and treatment is now considered an essential part of wound care. Many antimicrobial treatments, whether topical or systemic, have been shown to have limited efficacy in the treatment of biofilm phenotypes. The antimicrobial properties of iodine compounds rely on multiple and diverse interactions to exert their effects on microorganisms. An expert panel, held in Las Vegas during the autumn Symposium on Advanced Wound Care meeting in 2018, discussed these properties, with the focus on iodine and iodophors and their effects on biofilm prevention and treatment.

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.

Monitoring and controlling bacteria in pharmaceutical industries water system

AIM

This research aimed to monitor pharmaceutical water system by sampling water from all treatment stages, identify bacterial isolates from each phase and determine the most suitable methods to control them.

METHODS AND RESULTS

Water samples were collected and examined from pharmaceutical water system in a pharmaceutical factory in Giza, Egypt during 12 months, once per month (from December 2017 to November 2018) from 15 points covering all stages of the treatment process starting from wells, pre-treatment points; treatment points ending with purified points which are the main source of water used in all pharmaceutical process. In all, 216 water samples were collected and examined, 156 isolates were selected according to morphological characteristics. VITEK system 2 (BioMérieux) was used for identification of all isolates resulting in 24 different identified bacteria. Antibiotic assay test using disc diffusion methods were carried out using seven antibiotics from different groups. Several disinfectants were also examined for efficacy against the isolates to control micro-organisms in water treatment stage and manufacturing area. The effect of different preservatives (parabens, acids and alcohols) in various pharmaceutical formulas was also tested on bacterial isolates, 63% of formulas were effective against all bacterial isolates.

CONCLUSION

Ciprofloxacin was the most effective antibiotic, mixture of 0·45% peracetic acid plus 2·2% of hydrogen peroxide (Minncare 1%) was maximally effective disinfectant, and Cronobacter sakazakii was the most resistant micro-organism against 22·7% of tested preservatives.

SIGNIFICANCE AND IMPACT OF THE STUDY

Controlling pharmaceutical manufacturing operation from pathogenic bacteria that affect the quality of drugs.

In vitro antimicrobial effects of chlorhexidine diacetate versus chlorhexidine free base dressings

OBJECTIVE

The aim of this study was to investigate the in vitro antimicrobial performance of a chlorhexidine diacetate dressing and a chlorhexidine free base dressing to determine if the free base form of chlorhexidine has the potential to be an effective alternative to the chlorhexidine salts used in conventional, chlorhexidine-based antimicrobial dressings.

METHOD

Dressing samples were inoculated with clinically relevant pathogenic microorganisms including Gram-positive and Gram-negative bacteria, yeasts and fungus, and subsequently evaluated for in vitro log₁₀ reduction at 1-, 3-, and 7-day time points. Chlorhexidine mole content was also calculated as a function of dressing surface area for both sample types to allow for formulation-independent comparison between the dressings.

RESULTS

The chlorhexidine free base dressing demonstrated >0.5 log₁₀ superior mean antimicrobial efficacy at 67% of the experimental time points and equivalent mean antimicrobial efficacy (≤0.5 log₁₀ different) at the remaining time points when compared with the chlorhexidine diacetate dressing. The chlorhexidine free base dressing was also found to contain 36% less chlorhexidine mole content than the chlorhexidine diacetate dressing.

CONCLUSION

Our results suggest that a dressing formulated with chlorhexidine free base can deliver in vitro antimicrobial performance at both a magnitude and rate that meets or exceeds that of a chlorhexidine diacetate-based dressing, while also allowing for a reduction in total chlorhexidine content per dressing. These findings could be of particular interest to researchers developing new antimicrobial technologies as well as to infection preventionists when evaluating antimicrobial products for use on clinical patients at elevated risk of infection.

Clinical impact of an anti-biofilm Hydrofiber dressing in hard-to-heal wounds previously managed with traditional antimicrobial products and systemic antibiotics

Background

Hard-to-heal wounds are often compromised by the presence of biofilm. This presents an infection risk, yet traditional antimicrobial wound care products and systemic antibiotics are often used despite the uncertainty of therapeutic success and wound progression. The aim of this study was to investigate the clinical impact of a next-generation anti-biofilm Hydrofiber wound dressing (AQUACEL Ag+ Extra[AQAg+ E]) in hard-to-heal wounds that had previously been treated unsuccessfully with traditional silver-, iodine- or polyhexamethylene biguanide (PHMB)-containing dressings and products and/or systemic antibiotics.

Methods

Clinical case study evaluations of the anti-biofilm dressing were conducted, where deteriorating or stagnant wounds were selected by clinicians and primary dressings were replaced by the anti-biofilm dressing for up to 4 weeks, or as deemed clinically appropriate, with monitoring via case report forms. The data was stratified for cases where traditional silver-, iodine- or PHMB-containing products, or systemic antibiotics, had been used prior to the introduction of the anti-biofilm dressing.

Results

Sixty-five cases were identified for inclusion, wounds ranging in duration from 1 week to 20 years (median: 12 months). In 47 (72%) cases the wounds were stagnant, while 15 (23%) were deteriorating; 3 wounds were not recorded. After an average of 4.2 weeks of management with the anti-biofilm dressing (range: 1-11 weeks), in 11 (17%) cases the wounds had healed (i.e. complete wound closure), 40 (62%) wounds improved, 9 (14%) wounds remained the same and 5 (8%) wounds deteriorated.

Conclusions

The introduction of this anti-biofilm dressing into protocols of care that had previously involved wound management with traditional antimicrobial products and/or antibiotics was shown to facilitate improvements in the healing status of most of these hard-to-heal wounds. Dressings containing proven anti-biofilm technology, in combination with antimicrobial silver and exudate management technology, appear to be an effective alternative to traditional antimicrobial products and antibiotics in the cases presented here. The use of antimicrobial wound dressings that contain anti-biofilm technology may have a key role to play in more effective wound management and antibiotic stewardship.

Use of internally validated in vitro biofilm models to assess antibiofilm performance of silver-containing gelling fibre dressings

Objective:

To assess the efficacy of five silver-containing gelling fibre wound dressings against single-species and multispecies biofilms using internally validated, UKAS-accredited in vitro test models.

Method:

Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans single- and multispecies biofilms were cultured using Centres for Disease Control (CDC) biofilm reactors and colony drip flow reactors (CDFR). Following a 72 hour incubation period, the substrates on which biofilms were grown were rinsed to remove planktonic microorganisms and then challenged with fully hydrated silver-containing gelling fibre wound dressings. Following dressing application for 24 or 72 hours, remaining viable organisms from the treated biofilms were quantified.

Results:

In single-species in vitro models, all five antimicrobial dressings were effective in eradicating Staphylococcus aureus and Pseudomonas aeruginosa biofilm bacteria. However, only one of the five dressings (Hydrofiber technology with combination antibiofilm/antimicrobial technology) was able to eradicate the more tolerant single-species Candida albicans biofilm. In a more complex and stringent CDFR biofilm model, the hydrofiber dressing with combined antibiofilm/antimicrobial technology was the only dressing that was able to eradicate multispecies biofilms such that no viable organisms were recovered.

Conclusion:

Given the detrimental effects of biofilm on wound healing, stringent in vitro biofilm models are increasingly required to investigate the efficacy of antimicrobial dressings. Using accredited in vitro biofilm models of increasing complexity, differentiation in the performance of dressings with combined antibiofilm/antimicrobial technology against those with antimicrobial properties alone, was demonstrated.

A Surfactant-Based Dressing to Treat and Prevent Acinetobacter baumannii Biofilms

Previous work has demonstrated that a surfactant-based dressing was capable of eliminating any evidence of pre-existing biofilms from an ex vivo porcine skin wound model. Herein, the authors test both the surfactant's ability to prevent biofilm formation and its ability to eliminate Acinetobacter baumannii biofilms. To test biofilm formation inhibition, porcine skin explants were inoculated and incubated for 4 hours before treatment. The explants were then dressed with test or control materials. To test biofilm elimination, mature 3-day biofilms were established and then treated and wiped daily. Explants from each group were harvested daily, and total and biofilm-associated bacterial counts were generated up through day 3 posttreatment. The control explants developed a biofilm with ~106 CFU over the course of 3 days for each of the bacteria tested. The surfactant-treated samples had viable bacteria, but with the exception of a single time point for Staphylococcus aureus without silver sulfadiazine, there was no biofilm formation. Unlike previous results, the surfactants could not eliminate the A. baumannii biofilm, unless it was formulated with relevant antibiotics. The surfactant was effective in preventing the formation of biofilms over a 3-day period. Unlike the authors' previous results, the daily surfactant-based approach alone did not eliminate the A. baumannii biofilms unless relevant antibiotics were included. The data suggest that the surfactants can prevent biofilm formation, but that in the case of a confirmed A. baumannii biofilm, the surfactant must include antibiotics.

Electric Field Based Dressing Disrupts Mixed-Species Bacterial Biofilm Infection and Restores Functional Wound Healing

OBJECTIVE

This study was designed to employ electroceutical principles, as an alternative to pharmacological intervention, to manage wound biofilm infection. Mechanism of action of a United States Food and Drug Administration-cleared wireless electroceutical dressing (WED) was tested in an established porcine chronic wound polymicrobial biofilm infection model involving inoculation with Pseudomonas aeruginosa PAO1 and Acinetobacter baumannii 19606.

BACKGROUND

Bacterial biofilms represent a major wound complication. Resistance of biofilm toward pharmacologic interventions calls for alternative therapeutic strategies. Weak electric field has anti-biofilm properties. We have previously reported the development of WED involving patterned deposition of Ag and Zn on fabric. When moistened, WED generates a weak electric field without any external power supply and can be used as any other disposable dressing.

METHODS

WED dressing was applied within 2 hours of wound infection to test its ability to prevent biofilm formation. Alternatively, WED was applied after 7 days of infection to study disruption of established biofilm. Wounds were treated with placebo dressing or WED twice a week for 56 days.

RESULTS

Scanning electron microscopy demonstrated that WED prevented and disrupted wound biofilm aggregates. WED accelerated functional wound closure by restoring skin barrier function. WED blunted biofilm-induced expression of (1) P. aeruginosa quorum sensing mvfR (pqsR), rhlR and lasR genes, and (2) miR-9 and silencing of E-cadherin. E-cadherin is critically required for skin barrier function. Furthermore, WED rescued against biofilm-induced persistent inflammation by circumventing nuclear factor kappa B activation and its downstream cytokine responses.

CONCLUSION

This is the first pre-clinical porcine mechanistic study to recognize the potential of electroceuticals as an effective platform technology to combat wound biofilm infection.

Novel Antimicrobial Peptides Formulated in Chitosan Matrices are Effective Against Biofilms of Multidrug-Resistant Wound Pathogens

INTRODUCTION

Infection frequently complicates the treatment of combat-related wounds, impairs healing, and leads to worse outcomes. To better manage wound infections, antimicrobial therapies that are effective against biofilm and designed for direct wound application are needed. The primary objective of this work was to evaluate a chitosan matrix for delivery of two engineered antimicrobial peptides, (ASP)-1 and ASP-2, to treat biofilm-associated bacteria. A secondary objective was to determine whether replacing the levorotatory (L) form amino acids in ASP-2 with dextrorotatory (D) form amino acids would impact peptide activity.

MATERIALS AND METHODS

Chitosan gels loaded with antimicrobial peptides were evaluated for peptide release over 7 days and tested for efficacy against biofilms grown both in vitro on polymer mesh and ex vivo on porcine skin.

RESULTS

When delivered via chitosan, 70% to 80% of peptides were released over 7 days. Gels eradicated biofilms of gram-positive and gram-negative, drug-resistant bacteria in vitro and ex vivo. Under the conditions tested, no meaningful differences in peptide activity between the L and D forms of ASP-2 were detected.

CONCLUSIONS

Chitosan serves as an effective delivery platform for ASP-1 and ASP-2 to treat biofilm-embedded bacteria and warrants further development as a topical treatment.

The efficacy of topical agents used in wounds for managing chronic biofilm infections: A systematic review

OBJECTIVES

Clinicians have increasingly adopted the widespread use of topical agents to manage chronic wound infections, despite limited data on their effectiveness in vivo. This study sought to evaluate the evidence for commonly employed topical agents used in wounds for the purpose of treating chronic infections caused by biofilm.

METHOD

We included in vitro, animal and human in vivo studies where topical agents were tested for their efficacy against biofilms, for use in wound care. For human studies, we only included those which utilised appropriate identification techniques for visualising and confirming the presence of biofilms.

RESULT

A total of 640 articles were identified, with 43 included after meeting eligibility. In vitro testing accounted for 90% (n = 39) of all included studies, five studies using animal models and three human in vivo studies. Sixteen different laboratory models were utilised, with the most frequent being the minimum biofilm eradication concentration (MBEC™) / well plate assay (38%, n = 15 of 39). A total of 44 commercially available topical agents were grouped into twelve categories with the most commonly tested agents being silver, iodine and polyhexamethylene biguanide (PHMB). In vitro results on efficacy demonstrated iodine as having the highest mean log10 reductions of all agents (4.81, ±3.14).

CONCLUSION

There is large disparity in the translation of laboratory studies to researchers undertaking human trials relating to the effectiveness of commercially available topical agents. There is insufficient human in vivo evidence to definitively recommend any commercially available topical agent over another for the treatment of chronic wound biofilms. The heterogeneity identified between study designs (in vitro to in vivo) further limits the generalisability of results.

SPS-neutralization in tissue samples for efficacy testing of antimicrobial peptides

Background

Accurate determination of the efficacy of antimicrobial agents requires neutralization of residual antimicrobial activity in the samples before microbiological assessment of the number of surviving bacteria. Sodium polyanethol sulfonate (SPS) is a known neutralizer for the antimicrobial activity of aminoglycosides and polymyxins. In this study, we evaluated the ability of SPS to neutralize residual antimicrobial activity of antimicrobial peptides [SAAP-148 and pexiganan; 1% (wt/v) in PBS], antibiotics [mupirocin (Bactroban) and fusidic acid (Fucidin) in ointments; 2% (wt/wt))] and disinfectants [2% (wt/wt) silver sulfadiazine cream (SSD) and 0.5% (v/v) chlorhexidine in 70% alcohol].

Methods

Homogenates of human skin models that had been exposed to various antimicrobial agents for 1 h were pipetted on top of Methicillin-resistant Staphylococcus aureus (MRSA) on agar plates to determine whether the antimicrobial agents display residual activity.

To determine the optimal concentration of SPS for neutralization, antimicrobial agents were mixed with PBS or increasing doses of SPS in PBS (0.05–1% wt/v) and then 10⁵ colony forming units (CFU)/mL MRSA were added. After 30 min incubation, the number of viable bacteria was assessed. Next, the in vitro efficacy of SAAP-148 against various gram-positive and gram-negative bacteria was determined using PBS or 0.05% (wt/v) SPS immediately after 30 min incubation of the mixture. Additionally, ex vivo excision wound models were inoculated with 10⁵ CFU MRSA for 1 h and exposed to SAAP-148, pexiganan, chlorhexidine or PBS for 1 h. Subsequently, samples were homogenized in PBS or 0.05% (wt/v) SPS and the number of viable bacteria was assessed.

Results

All tested antimicrobials displayed residual activity in tissue samples, resulting in a lower recovery of surviving bacteria on agar. SPS concentrations at ≥0.05% (wt/v) were able to neutralize the antimicrobial activity of SAAP-148, pexiganan and chlorhexidine, but not of SSD, Bactroban and Fucidin. Finally, SPS-neutralization in in vitro and ex vivo efficacy tests of SAAP-148, pexiganan and chlorhexidine against gram-positive and gram-negative bacteria resulted in significantly higher numbers of CFU compared to control samples without SPS-neutralization.

Conclusions

SPS was successfully used to neutralize residual activity of SAAP-148, pexiganan and chlorhexidine and this prevented an overestimation of their efficacy.

Evaluation of Drug Delivery and Efficacy of Ciprofloxacin-Loaded Povidone Foils and Nanofiber Mats in a Wound-Infection Model Based on Ex Vivo Human Skin

Topical treatment of wound infections is often a challenge due to limited drug availability at the site of infection. Topical drug delivery is an attractive option for reducing systemic side effects, provided that a more selective and sustained local drug delivery is achieved. In this study, a poorly water-soluble antibiotic, ciprofloxacin, was loaded on polyvinylpyrrolidone (PVP)-based foils and nanofiber mats using acetic acid as a solubilizer. Drug delivery kinetics, local toxicity, and antimicrobial activity were tested on an ex vivo wound model based on full-thickness human skin. Wounds of 5 mm in diameter were created on 1.5 × 1.5 cm skin blocks and treated with the investigated materials. While nanofiber mats reached the highest amount of delivered drug after 6 h, foils rapidly achieved a maximum drug concentration and maintained it over 24 h. The treatment had no effect on the overall skin metabolic activity but influenced the wound healing process, as observed using histological analysis. Both delivery systems were efficient in preventing the growth of Pseudomonas aeruginosa biofilms in ex vivo human skin. Interestingly, foils loaded with 500 µg of ciprofloxacin accomplished the complete eradication of biofilm infections with 1 × 109 bacteria/wound. We conclude that antimicrobial-loaded resorbable PVP foils and nanofiber mats are promising delivery systems for the prevention or topical treatment of infected wounds.

Clinical and in vitro performance of an antibiofilm Hydrofiber wound dressing

OBJECTIVE

To compare the clinical and in vitro performance of a next-generation antibiofilm silver dressing (NGAD) with an established antimicrobial dressing technology that was developed before the recognition of wound biofilm as a clinical challenge.

METHOD

Real-life evaluations of challenging wounds managed previously with cadexomer iodine (CI) dressings followed by switching to NGAD were evaluated alongside electron, confocal and light microscopy images from a challenging, in vitro, exuding chronic wound model. Clinical case studies on the use of CI and NGAD dressings are presented to further explore the real-life evidence and in vitro findings.

RESULTS

We assessed 13 non-healing wounds that had been managed with protocols including CI dressings. After a median of four weeks, switching to the NGAD as primary dressing resulted in improvements in nine wounds and healing in two wounds, with associated improvements in wound bed appearance, while dressing usage was the same as or lower than before. The NGAD was observed to prevent the development of Staphylococcus aureus- Pseudomonas aeruginosa biofilm over three days, in contrast to the CI dressing, which appeared to support biofilm development once the active antimicrobial was exhausted from its carrier material. Clinical case studies exhibited this exhaustion as 'whiting out' of the dressing, with wound biofilm observed from samples taken following dressing use. Positive wound and patient outcomes were observed in two cases following the switch from a CI primary dressing to the NGAD, in highly exuding and infected wounds.

CONCLUSION

Antimicrobial dressings may be effective against biofilm in some laboratory models, but their effectiveness as a wound dressings in protocols of care must be verified clinically.

Air-fluidized therapy in the treatment of severe burns: A retrospective study from a burn intensive care unit in Austria

INTRODUCTION

Air-fluidized therapy (AFT) has long been used in the treatment of severe burns. In patients with extensive burns involving the posterior trunk, we aim to keep affected posterior areas dry and to postpone their treatment, initially applying available split-thickness skin grafts in functionally more important regions. We retrospectively assessed the impact of AFT on the survival of patients treated in the burn intensive care unit (ICU) of the Medical University of Vienna, Austria, between 2003 and 2016.

METHODS

This retrospective single-center study included patients aged ≥18 years with burned total body surface area (TBSA) ≥20% and IIb-III° thermal injuries on the posterior trunk who received AFT. Survival rates were compared with those predicted by the abbreviated burn severity index (ABSI). Demographic, clinical, and surgical data were analyzed.

RESULTS

Seventy-five of 110 patients with posterior trunk burns received AFT. Their survival rate exceeded that predicted by the ABSI score (mean ABSI, 10.0 ± 2.0; 73.3% (95% CI: 62-83%) survival rate vs. 20-40% predicted; p <  0.0001); no such difference was observed in the non-AFT group (mean, 8.8 ± 1.9; 65.7% (95% CI: 48-81%) survival rate vs. 50-70% predicted). Patients receiving AFT had significantly greater TBSA (median, 50% (35-60) vs. 30% (25-45) and longer ICU stays (median, 63 (36-92) vs. 18 (9-52) days; both p <  0.0001). Fifty-one (68.0%) patients in the AFT group and 26 (74.3%) patients in the non-AFT group underwent posterior trunk surgery (p =  0.66) a median of 16 (10-26) and 5 (2.5-9.5) days, respectively, after admission (p <  0.0001).

CONCLUSIONS

Patients receiving AFT had significantly better survival than predicted by ABSI score in contrast to patients not receiving AFT although burn injuries in this group were more severe (greater TBSA, higher ABSI). As intensive care was similar in these groups aside from AFT, the better survival could be attributed to this additional therapy.

Evolving concepts in bone infection: redefining "biofilm", "acute vs. chronic osteomyelitis", "the immune proteome" and "local antibiotic therapy"

Osteomyelitis is a devastating disease caused by microbial infection of bone. While the frequency of infection following elective orthopedic surgery is low, rates of reinfection are disturbingly high. Staphylococcus aureus is responsible for the majority of chronic osteomyelitis cases and is often considered to be incurable due to bacterial persistence deep within bone. Unfortunately, there is no consensus on clinical classifications of osteomyelitis and the ensuing treatment algorithm. Given the high patient morbidity, mortality, and economic burden caused by osteomyelitis, it is important to elucidate mechanisms of bone infection to inform novel strategies for prevention and curative treatment. Recent discoveries in this field have identified three distinct reservoirs of bacterial biofilm including: Staphylococcal abscess communities in the local soft tissue and bone marrow, glycocalyx formation on implant hardware and necrotic tissue, and colonization of the osteocyte-lacuno canalicular network (OLCN) of cortical bone. In contrast, S. aureus intracellular persistence in bone cells has not been substantiated in vivo, which challenges this mode of chronic osteomyelitis. There have also been major advances in our understanding of the immune proteome against S. aureus, from clinical studies of serum antibodies and media enriched for newly synthesized antibodies (MENSA), which may provide new opportunities for osteomyelitis diagnosis, prognosis, and vaccine development. Finally, novel therapies such as antimicrobial implant coatings and antibiotic impregnated 3D-printed scaffolds represent promising strategies for preventing and managing this devastating disease. Here, we review these recent advances and highlight translational opportunities towards a cure.

Effects and efficacy of different sterilization and disinfection methods on electrospun drug delivery systems

Microbiological quality of a pharmaceutical product is an essential requirement ensuring patient safety, thus effective sterilization/disinfection methods need to be found. The aim of this study was to evaluate the efficacy of different sterilization/disinfection methods on drug-loaded electrospun matrices and the impact of these treatments on the functionality related characteristics of these matrices. The sterilization efficacy of gamma-irradiation, ultraviolet-irradiation, in situ generated chlorine gas and low-pressure argon plasma treatment were evaluated on two different chloramphenicol-loaded electrospun matrices using pristine polycaprolactone (PCL) as a carrier polymer or PCL in combination with polyethylene oxide. Drug stability, solid state properties, morphology, mechanical properties, swelling, biodegradation and drug release kinetics were studied before and after the treatments. It was shown that all tested methods help to reduce bioburden and only plasma treated matrices were not sterile. At the same time drug degradation after the treatment can be considerable and depends not only on the susceptibility of the drug to degradation, but also on matrix properties (e.g. the nature of carrier polymers). Even though no morphological changes were observed, gamma sterilization increased the hardness and elasticity of PCL matrices as a result of increased crystallinity of the polymer. Plasma treatment was able to significantly enhance water absorption to otherwise hydrophobic PCL/CAM matrix and had tremendous impact on its drug release kinetics as the drug was instantly released from otherwise prolonged release formulation.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Cadexomer iodine effectively reduces bacterial biofilm in porcine wounds ex vivo and in vivo

Biofilms are prevalent in non-healing chronic wounds and implicated in delayed healing. Tolerance to antimicrobial treatments and the host's immune system leave clinicians with limited interventions against biofilm populations. It is therefore essential that effective treatments be rigorously tested and demonstrate an impact on biofilm across multiple experimental models to guide clinical investigations and protocols. Cadexomer iodine has previously been shown to be effective against biofilm in various in vitro models, against methicillin-resistant Staphylococcus aureus biofilm in mouse wounds, and clinically in diabetic foot ulcers complicated by biofilm. Similarities between porcine and human skin make the pig a favoured model for cutaneous wound studies. Two antiseptic dressings and a gauze control were assessed against mature biofilm grown on ex vivo pig skin and in a pig wound model. Significant reductions in biofilm were observed following treatment with cadexomer iodine across both biofilm models. In contrast, silver carboxymethylcellulose dressings had minimal impact on biofilm in the models, with similar results to the control in the ex vivo model. Microscopy and histopathology indicate that the depth of organisms in wound tissue may impact treatment effectiveness. Further work on the promising biofilm efficacy of cadexomer iodine is needed to determine optimal treatment durations against biofilm.