A novel chronic wound biofilm model sustaining coexistence of Pseudomonas aeruginosa and Staphylococcus aureus suitable for testing of antibiofilm effect of antimicrobial solutions and wound dressings

An In Vitro Artificial Wound Slough-Biofilm Model Developed for Evaluating a Novel Antibiofilm Technology

Eschar and slough in wounds serve as a reservoir for microorganisms and biofilms, damaged/devitalised cells, and inflammatory chemokines/cytokines, which work to initiate and prolong persistent inflammation and increase the risk of infection. Biofilm-related inflammation and infections are considered to be highly prevalent in acute wounds and chronic wounds. As slough is known to harbour biofilms, measuring the efficacy of antimicrobials in killing microbes both within and under slough is warranted. This highlights the need for more clinically relevant wound biofilm models to address this significant clinical need. Consequently, in this study, we developed an in vitro artificial wound slough (AWS) biofilm model produced by forming a biofilm below a layer of AWS, the latter of which was composed of the main protein components reported in wound eschar and slough, namely collagen, elastin, and fibrin. The model was employed to investigate the antibiofilm and antibacterial efficacy of a new patented smart next-generation antibiofilm technology composed of silver-zinc EDTA complexes and designed as a family of multifunctional metal complexes referred to as MMCs, in a liquid format, and to determine both the performance and penetration through AWS to control and manage biofilms. The results demonstrated the ability of the AWS-biofilm model to be employed for the evaluation of the efficacy of a new antibiofilm and antimicrobial next-generation smart technology. The results also demonstrated the potential for the proprietary EDTA multifunctional metal complexes to be used for the disruption of biofilms, such as those that form in chronic wounds.

Cuminaldehyde in combination with tetracycline shows promising antibiofilm activity against drug-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen often causes biofilm-linked infections. A combinatorial approach involving tetracycline (antibiotic) and cuminaldehyde (phytochemical) was explored to combat this infectious pathogen. The results showed that both tetracycline and cuminaldehyde individually demonstrated antibacterial effects. However, when the compounds were applied together, there was a significant increase in their antimicrobial potential. The determined fractional inhibitory concentration index of 0.43 indicated a synergistic interaction between the two compounds. Furthermore, a series of experiments demonstrated that the combined application of cuminaldehyde and tetracycline could lead to a significant enhancement of their antibiofilm potential. This enhanced antibiofilm potential was attributed to the accumulation of reactive oxygen species and increased cell membrane permeability. Besides, this combinatorial application reduced the secretion of various virulence factors from P. aeruginosa. Therefore, this combined approach holds promise for effectively treating P. aeruginosa biofilms.

Plasma activated water as a pre-treatment strategy in the context of biofilm-infected chronic wounds

Healing and treatment of chronic wounds are often complicated due to biofilm formation by pathogens. Here, the efficacy of plasma activated water (PAW) as a pre-treatment strategy has been investigated prior to the application of topical antiseptics polyhexamethylene biguanide, povidone iodine, and MediHoney, which are routinely used to treat chronic wounds. The efficacy of this treatment strategy was determined against biofilms of Escherichia coli formed on a plastic substratum and on a human keratinocyte monolayer substratum used as an in vitro biofilm-skin epithelial cell model. PAW pre-treatment greatly increased the killing efficacy of all the three antiseptics to eradicate the E. coli biofilms formed on the plastic and keratinocyte substrates. However, the efficacy of the combined PAW-antiseptic treatment and single treatments using PAW or antiseptic alone was lower for biofilms formed in the in vitro biofilm-skin epithelial cell model compared to the plastic substratum. Scavenging assays demonstrated that reactive species present within the PAW were largely responsible for its anti-biofilm activity. PAW treatment resulted in significant intracellular reactive oxygen and nitrogen species accumulation within the E. coli biofilms, while also rapidly acting on the microbial membrane leading to outer membrane permeabilisation and depolarisation. Together, these factors contribute to significant cell death, potentiating the antibacterial effect of the assessed antiseptics.

Solving polymicrobial puzzles: evolutionary dynamics and future directions

Polymicrobial infections include various microorganisms, often necessitating different treatment methods than a monomicrobial infection. Scientists have been puzzled by the complex interactions within these communities for generations. The presence of specific microorganisms warrants a chronic infection and impacts crucial factors such as virulence and antibiotic susceptibility. Game theory is valuable for scenarios involving multiple decision-makers, but its relevance to polymicrobial infections is limited. Eco-evolutionary dynamics introduce causation for multiple proteomic interactions like metabolic syntropy and niche segregation. The review culminates both these giants to form evolutionary dynamics (ED). There is a significant amount of literature on inter-bacterial interactions that remain unsynchronised. Such raw data can only be moulded by analysing the ED involved. The review culminates the inter-bacterial interactions in multiple clinically relevant polymicrobial infections like chronic wounds, CAUTI, otitis media and dental carries. The data is further moulded with ED to analyse the niche colonisation of two notoriously competitive bacteria: S.aureus and P.aeruginosa. The review attempts to develop a future trajectory for polymicrobial research by following recent innovative strategies incorporating ED to curb polymicrobial infections.

Culture Shock: An Investigation into the Tolerance of Pathogenic Biofilms to Antiseptics in Environments Resembling the Chronic Wound Milieu

Credible assessment methods must be applied to evaluate antiseptics' in vitro activity reliably. Studies indicate that the medium for biofilm culturing should resemble the conditions present at the site of infection. We cultured S. aureus, S. epidermidis, P. aeruginosa, C. albicans, and E. coli biofilms in IVWM (In Vitro Wound Milieu)-the medium reflecting wound milieu-and were compared to the ones cultured in the laboratory microbiological Mueller-Hinton (MH) medium. We analyzed and compared crucial biofilm characteristics and treated microbes with polyhexamethylene biguanide hydrochloride (PHMB), povidone-iodine (PVP-I), and super-oxidized solution with hypochlorites (SOHs). Biofilm biomass of S. aureus and S. epidermidis was higher in IVWM than in MH medium. Microbes cultured in IVWM exhibited greater metabolic activity and thickness than in MH medium. Biofilm of the majority of microbial species was more resistant to PHMB and PVP-I in the IVWM than in the MH medium. P. aeruginosa displayed a two-fold lower MBEC value of PHMB in the IVWM than in the MH medium. PHMB was more effective in the IVWM than in the MH medium against S. aureus biofilm cultured on a biocellulose carrier (instead of polystyrene). The applied improvement of the standard in vitro methodology allows us to predict the effects of treatment of non-healing wounds with specific antiseptics.

A collagen-based layered chronic wound biofilm model for testing antimicrobial wound products

A new in vitro chronic wound biofilm model was recently published, which provided a layered scaffold simulating mammalian tissue composition on which topical wound care products could be tested. In this paper, we updated the model even further to mimic the dynamic influx of nutrients from below as is the case in a chronic wound. The modified in vitro model was created using collagen instead of agar as the main matrix component and contained both Staphylococcus aureus and Pseudomonas aeruginosa. The model was cast in transwell inserts and then placed in wound simulating media, which allowed for an exchange of nutrients and waste products across a filter. Three potential wound care products and chlorhexidine digluconate 2% solution as a positive control were used to evaluate the model. The tested products were composed of hydrogels made from completely biodegradable starch microspheres carrying different active compounds. The compounds were applied topically and left for 2-4 days. Profiles of oxygen concentration and pH were measured to assess the effect of treatments on bacterial activity. Confocal microscope images were obtained of the models to visualise the existence of microcolonies. Results showed that the modified in vitro model maintained a stable number of the two bacterial species over 6 days. In untreated models, steep oxygen gradients developed and pH increased to >8.0. Hydrogels containing active compounds alleviated the high oxygen consumption and decreased pH drastically. Moreover, all three hydrogels reduced the colony forming units significantly and to a larger extent than the chlorhexidine control treatment. Overall, the modified model expressed several characteristics similar to in vivo chronic wounds.

In vitro Antibacterial Activity and Wound Healing Effects of Achillea millefolium Essential Oil in Rat

Objectives

In this study we aimed to evaluate the in vitro antibacterial activity and wound healing properties of Achillea millefolium essential oil (AMEO) in full-thickness wound model in rat. The antibacterial activity of AMEO was evaluated against Staphylococcus aureus and Pseudomonas aeruginosa using the broth dilution method.

Methods

The 2 cm × 2 cm full-thickness excisional wounds were created on the back of animals. Topical therapy was applied twice a day using 1%, 2%, and 3% w/w AMEO ointments, and the measurement of the wounds area was carried out every 3 days, after that the wound closure percentage was calculated in these days. Hydroxyproline content and histopathological evaluation of wound tissue samples were carried out on day 7 and 14 post wounding. Eucerin was used for the treatment of vehicle control group and negative control group received no treatment.

Results

Our results revealed the bacteriostatic activity of AMEO against S. aureus and P. aeruginosa. Wound healing activity evaluation of AMEO showed the significant increase (p < 0.05) in the wound closure percentages in rats treated with AMEO 1% and 2% comparing to those of non-treatment group. In addition, hydroxyproline contents of tissue significantly (p < 0.01) increased in AMEO 1% and 2% comparing to non-treatment group. Histopathological evaluations of wound tissue samples on day 7 and 14 demonstrated higher accumulation of collagen fibers, reduction of edema and inflammation and also formation of tissue appendages in 1% and 2% AMEO treated groups in comparison with non-treatment group.

Conclusion

The results of this study indicated that AMEO has the potential to be used as a safe and effective wound healing agent.

In Vitro Models of Bacterial Biofilms: Innovative Tools to Improve Understanding and Treatment of Infections

Bacterial infections are a growing concern to the health care systems. Bacteria in the human body are often found embedded in a dense 3D structure, the biofilm, which makes their eradication even more challenging. Indeed, bacteria in biofilm are protected from external hazards and are more prone to develop antibiotic resistance. Moreover, biofilms are highly heterogeneous, with properties dependent on the bacteria species, the anatomic localization, and the nutrient/flow conditions. Therefore, antibiotic screening and testing would strongly benefit from reliable in vitro models of bacterial biofilms. This review article summarizes the main features of biofilms, with particular focus on parameters affecting biofilm composition and mechanical properties. Moreover, a thorough overview of the in vitro biofilm models recently developed is presented, focusing on both traditional and advanced approaches. Static, dynamic, and microcosm models are described, and their main features, advantages, and disadvantages are compared and discussed.

Larval Therapy and Larval Excretions/Secretions: A Potential Treatment for Biofilm in Chronic Wounds? A Systematic Review

Chronic wounds present a global healthcare challenge and are increasing in prevalence, with bacterial biofilms being the primary roadblock to healing in most cases. A systematic review of the to-date knowledge on larval therapy's interaction with chronic-wound biofilm is presented here. The findings detail how larval therapy-the controlled application of necrophagous blowfly larvae-acts on biofilms produced by chronic-wound-relevant bacteria through their principle pharmacological mode of action: the secretion and excretion of biologically active substances into the wound bed. A total of 12 inclusion-criteria-meeting publications were identified following the application of a PRISMA-guided methodology for a systematic review. The findings of these publications were qualitatively analyzed to provide a summary of the prevailing understanding of larval therapy's effects on bacterial biofilm. A further review assessed the quality of the existing evidence to identify knowledge gaps and suggest ways these may be bridged. In summary, larval therapy has a seemingly unarguable ability to inhibit and degrade bacterial biofilms associated with impaired wound healing. However, further research is needed to clarify and standardize the methodological approach in this area of investigation. Such research may lead to the clinical application of larval therapy or derivative treatments for the management of chronic-wound biofilms and improve patient healing outcomes at a time when alternative therapies are desperately needed.

There Is More to Wounds than Bacteria: Fungal Biofilms in Chronic Wounds

Purpose of Review

The management of chronic wounds, a debilitating condition, presents a considerable challenge to healthcare professionals and a significant burden on services. When these wounds are exposed to the external environment, they are susceptible to microbial infection, which further complicates their management and worsens clinical outcomes.

Recent Findings

Bacteria typically exist in wounds as part of a biofilm, which is often polymicrobial in nature, alongside bacteria and fungi that are described as being more virulent and tolerant towards antimicrobials and antiseptics. Despite advancing knowledge in polymicrobial biofilm wound infections with respect to bacteria, the role of fungi is largely ignored, and their influence in chronicity and clinical management is not fully appreciated or understood.

Summary

The purpose of this review is to explore the significance of fungi within chronic wound environments and, in doing so, understand the importance of interkingdom interactions in wound management.

Biofilms in Chronic Wound Infections: Innovative Antimicrobial Approaches Using the In Vitro Lubbock Chronic Wound Biofilm Model

Chronic wounds have harmful effects on both patients and healthcare systems. Wound chronicity is attributed to an impaired healing process due to several host and local factors that affect healing pathways. The resulting ulcers contain a wide variety of microorganisms that are mostly resistant to antimicrobials and possess the ability to form mono/poly-microbial biofilms. The search for new, effective and safe compounds to handle chronic wounds has come a long way throughout the history of medicine, which has included several studies and trials of conventional treatments. Treatments focus on fighting the microbial colonization that develops in the wound by multidrug resistant pathogens. The development of molecular medicine, especially in antibacterial agents, needs an in vitro model similar to the in vivo chronic wound environment to evaluate the efficacy of antimicrobial agents. The Lubbock chronic wound biofilm (LCWB) model is an in vitro model developed to mimic the pathogen colonization and the biofilm formation of a real chronic wound, and it is suitable to screen the antibacterial activity of innovative compounds. In this review, we focused on the characteristics of chronic wound biofilms and the contribution of the LCWB model both to the study of wound poly-microbial biofilms and as a model for novel treatment strategies.

Adding a new dimension: Multi-level structure and organization of mixed-species Pseudomonas aeruginosa and Staphylococcus aureus biofilms in a 4-D wound microenvironment

Biofilms in wounds typically consist of aggregates of bacteria, most often Pseudomonas aeruginosa and Staphylococcus aureus, in close association with each other and the host microenvironment. Given this, the interplay across host and microbial elements, including the biochemical and nutrient profile of the microenvironment, likely influences the structure and organization of wound biofilms. While clinical studies, in vivo and ex vivo model systems have provided insights into the distribution of P. aeruginosa and S. aureus in wounds, they are limited in their ability to provide a detailed characterization of biofilm structure and organization across the host-microbial interface. On the other hand, biomimetic in vitro systems, such as host cell surfaces and simulant media conditions, albeit reductionist, have been shown to support the co-existence of P. aeruginosa and S. aureus biofilms, with species-dependent localization patterns and interspecies interactions. Therefore, composite in vitro models that bring together key features of the wound microenvironment could provide unprecedented insights into the structure and organization of mixed-species biofilms. We have built a four-dimensional (4-D) wound microenvironment consisting of a 3-D host cell scaffold of co-cultured human epidermal keratinocytes and dermal fibroblasts, and an in vitro wound milieu (IVWM); the IVWM provides the fourth dimension that represents the biochemical and nutrient profile of the wound infection state. We leveraged this 4-D wound microenvironment, in comparison with biofilms in IVWM alone and standard laboratory media, to probe the structure of mixed-species P. aeruginosa and S. aureus biofilms across multiple levels of organization such as aggregate dimensions and biomass thickness, species co-localization and spatial organization within the biomass, overall biomass composition and interspecies interactions. In doing so, the 4-D wound microenvironment platform provides multi-level insights into the structure of mixed-species biofilms, which we incorporate into the current understanding of P. aeruginosa and S. aureus organization in the wound bed.

3D Biofilm Models Containing Multiple Species for Antimicrobial Testing of Wound Dressings

The treatment of chronic wounds presents a major challenge in medical care. In particular, the effective treatment of bacterial infections that occur in the form of biofilms is of crucial importance. To develop successful antibiofilm strategies for chronic wound treatment, biofilm models are needed that resemble the in vivo situation, are easy to handle, standardizable, and where results are readily transferable to the clinical situation. We established two 3D biofilm models to distinguish the effectiveness of wound dressings on important microorganisms present in chronic wounds. The first 3D biofilm model contains Staphylococcus aureus, Escherichia coli, and Acinetobacter baumannii, while the second is based on Pseudomonas aeruginosa. Bacteria are cultivated in a nutrient-rich agar/gelatin mix, into which air bubbles are incorporated. This results in a mature biofilm growing in clusters similar to its organization in chronic wounds. The models are convenient to use, have low variability and are easy to establish in the laboratory. Treatment with polihexanide and silver-containing wound dressings showed that the models are very well suited for antimicrobial testing and that they can detect differences in the efficacy of antimicrobial substances. Therefore, these models present valuable tools in the development of effective antibiofilm strategies in chronic wounds.

The cross-linked bacterial cellulose impregnated with octenidine dihydrochloride-based antiseptic as an antibacterial dressing material for highly-exuding, infected wounds

The highly absorbent, antibacterial dressings with a sustained release of the antimicrobial are considered necessary measures to counteract chronic wound biofilm-based infections. This study aimed to analyze wet and dry bacterial cellulose (BC) materials, modified by chemical cross-linking, and impregnated with an antiseptic based on octenidine dihydrochloride (OCT) in the context of its antibiofilm/antibacterial activity, exudate absorption, and cytotoxicity. The native BC was obtained from cost-effective, ecological-friendly potato juice (leftover from the starch industry). The ability to absorb and retain OCT, exudate absorption capacity, the kinetics of OCT release as well as antibiofilm/antibacterial activity of modified BC materials against biofilm-forming and planktonic bacteria (Staphylococcus aureus and Pseudomonas aeruginosa) were investigated. The performed analyses revealed that modified BC materials, thanks to their layered structure with numerous air spaces, were characterized by sustained exudate absorption and OCT release profile, which allowed them to exhibit high antimicrobial activity for up to 7 days, with a reduction of planktonic and biofilm cells of 84-100% and 69-93%, respectively. The modified BC materials showed also no cytotoxicity against fibroblast cell line L929 in vitro and were characterized by firm adhesion to the curved surfaces. These results indicate that cross-linked BC impregnated with OCT may be a particularly promising dressing material (obtained using sustainable processes), especially in the treatment of biofilm-infected, highly-exuding wounds.

Clinically relevant in vitro biofilm models: A need to mimic and recapitulate the host environment

Biofilm-associated infections are difficult to treat and eradicate because of their increased antimicrobial tolerance. In vitro biofilm models have enabled the high throughput testing of an array of differing novel antimicrobials and treatment strategies. However, biofilms formed in these oftentimes basic in vitro systems do not resemble biofilms seen in vivo. As a result, translatability from the lab to the clinic is poor or limited. To improve translatability, in vitro models must better recapitulate the host environment. This review describes and critically evaluates new and innovative in vitro models that better mimic the environments of a variety of clinically important, biofilm-associated infections of the skin, oropharynx, lungs, and infections related to indwelling implants and medical devices. This review highlights that many of these models represent considerable advances in the field of biofilm research and help to translate laboratory findings into the clinical practice.

Saudi Honey: A Promising Therapeutic Agent for Treating Wound Infections

Treatment of wounds, especially chronic ones, is a major challenge in healthcare, with serious clinical and economic burdens. Multiple treatment approaches, including the usage of silver and iodine, have dramatically improved wound healing and reduced the incidence of infection. However, once infected by drug-resistant bacteria, treatment of wounds becomes a serious complication, with limited availability of effective antibiotic drugs, leading to high morbidity and mortality. Therefore, alternative therapeutic agents are required to address this gap in wound management. The introduction of manuka honey as a therapeutic agent against infected wounds was the result of extensive research about its activity against both planktonic and biofilm bacterial growth. Likewise, several types of Saudi honey (e.g., Sidr and Talh) showed promising in vitro and in vivo antimicrobial activity against wound pathogens. This short review summarizes literature that investigated the activity of common types of Saudi honey in relation to wound infections and explores their clinical utility.