Novel models for bacterial colonization and infection of full-thickness wounds in rats

The rat as an animal model in chronic wound research: An update

The increasing global prevalence of chronic wounds underscores the growing importance of developing effective animal models for their study. This review offers a critical evaluation of the strengths and limitations of rat models frequently employed in chronic wound research and proposes potential improvements. It explores these models in the context of key comorbidities, including diabetes, venous and arterial insufficiency, pressure-induced blood flow obstruction, and infections. Additionally, the review examines important wound factors including age, sex, smoking, and the impact of anesthetic and analgesic drugs, acknowledging their substantial effects on research outcomes. A thorough understanding of these variables is crucial for refining animal models and can provide valuable insights for future research endeavors.

Local low-frequency vibration accelerates healing of full-thickness wounds in a hyperglycemic rat model

AIMS/INTRODUCTION

Local low-frequency vibration (LLFV) promotes vasodilation and blood flow, enhancing wound healing in diabetic foot ulcers with angiopathy. However, vibration-induced vasodilation does not occur, owing to chronic hyperglycemia and inflammation. We hypothesized that LLFV improves glycometabolism and inflammation, leading to vasodilation and angiogenesis in diabetic wounds. Therefore, this study investigated the effect of LLFV on wound healing in hyperglycemic rats, primarily focusing on glycometabolism, inflammation, vasodilation, and angiogenesis.

MATERIALS AND METHODS

Streptozotocin-induced hyperglycemic Sprague-Dawley rats were used in this study. We applied LLFV to experimentally-induced wounds at 50 Hz and 0, 600, 1,000 or 1,500 mVpp for 40 min/day from post-wounding days (PWD) 1-14.

RESULTS

The relative wound areas in the 600 and 1,000 mVpp groups on PWD 5-7 were significantly smaller than those at 0 mVpp. The expression of Glo-1 (1,500 mVpp) and Slc2A4 (1,000 and 1,500 mVpp) was upregulated on PWD 4 and 14, respectively. However, there was no difference in methylglyoxal expression levels in any group until PWD 14. At 1,000 mVpp, the expression of Tnfa on PWD 4, and that of Ptx3 and Ccl2 on PWD 14 was downregulated. Furthermore, the M1/M2 macrophage ratio was considerably decreased on both days. The expression of Nos3, Vegfa and vascular endothelial growth factor A was upregulated on PWD 4. In addition, vasodilation and angiogenesis were more obvious on PWD 14 with 1,000 mVpp.

CONCLUSIONS

The results suggest that LLFV promotes wound healing, improves glycometabolism and inflammation, and enhances vasodilation and angiogenesis in hyperglycemic wounds.

Efficacy of wearable vibration dressings on full-thickness wound healing in a hyperglycemic rat model

Local low-frequency vibration promotes blood flow and wound healing in hard-to-heal diabetic foot ulcers (DFUs). However, vibration treatment is challenging in patients with DFUs due to wound management difficulties and low adherence. Consequently, developing wearable self-care devices becomes imperative for effective wound healing. This study introduces a wearable vibration dressing and assesses its impact on wound healing in hyperglycemic rats. Low-frequency vibration at 52 Hz was applied to the wound for 40 min/day in awake rats. Relative wound areas on post-wounding days (PWDs) 4-7 were significantly smaller and the wound closure rate was significantly higher in the vibration group than in the control group (p < 0.05, respectively). The total haemoglobin at baseline and after vibration on post-wounding day 7 was significantly larger in the vibration group than in the control group (p < 0.05). On PWD 7, the thickness of the granulation tissue was significantly higher in the vibration group than in the control group (p < 0.05). Moreover, the number of blood vessels at the wound site and vascular endothelial growth factor A protein expression were significantly higher in the vibration group than in the control group (p < 0.05, respectively). The ratio of (CD68+ /iNOS+ )/(CD163+ ) macrophages in the vibration group was significantly lower than that in the control group (p < 0.05). These results indicate the potential of wearable vibration dressings as new self-care devices that can promote angiogenesis and blood flow, improve inflammation, and enhance wound healing in DFUs.

An in vivo critically colonised wound model with dysbiotic wound microbiota

In critically colonised wounds, many of the signs of infection are often absent, and delayed healing may be the only clinical sign. The prevention of critical colonisation is important, but its pathophysiology has not yet been elucidated. We have previously reported that dysbiotic microbiota dissimilar to the peri-wound skin microbiota may develop in critically colonised wounds. To investigate the role of dysbiotic microbiota, this study aimed to develop a critically colonised wound model by transplantation of dysbiotic microbiota. To transplant microbiota, a bacterial solution (dysbiosis group) or with Luria-Bertani medium (commensal group) was inoculated to full-thickness wounds of rats. The bacterial solution was prepared by anaerobically culturing bacteria from donor rats on an artificial dermis in Luria-Bertani medium for 72 hours. As a result, the degree of the change in the microbial similarity between pre- and post-transplantation of microbiota was significantly higher in the dysbiosis group (P < .001). No signs of infection were observed in any rat in either group. The wound area in the dysbiosis group was significantly larger (P < .001), and there was a significant infiltration of neutrophils (P < .001). All rats of the dysbiosis group represented the clinical features of critically colonised wounds. Furthermore, there were significantly fewer regulatory T cells in the wounds of the dysbiosis group. This is the first study to develop a novel animal model that represents the clinical features of critically colonised wounds and will be useful in investigating the pathogenesis of critical colonisation via regulatory T cells.

The effect of NPWT in wound healing and bacterial count on deep dermal burn injury model: An experimental study

Background

Sepsis is one of the main causes in burn victim's mortality. The use of negative pressure wound therapy (NPWT) provides an ideal environment to accelerate wound healing. We compare the use of normal saline (NS), intermittent NPWT, continuous NPWT and silver sulfadiazine in wound healing process.

Method

This study involved 6 Yorkshire pigs; each pig was induced with 20 burns on the flank area. Burns were divided into 4 treatment groups: NS gauze, intermittent NPWT, continuous NPWT, and silver sulfadiazine dressing. Burns were evaluated on day 1,3,7,14, and 21 for its morphology and bacterial colonization and on day 14 and 21 for the remaining burn surface area.

Result

Wound that received NPWT therapy appeared better in both granulation and crust formation. Remaining burn surface area (mm²) on day 14 in NS group, intermittent NPWT, continuous NPWT, and silver sulfadiazine were 107.43 ± 83.43, 178.07 ± 74.83, 146.10 ± 69.1, 126.03 ± 83.22, respectively(p = 0.457); on day 21 in NS group, intermittent NPWT, continuous NPWT, and silver sulfadiazine were 13.16 ± 16.86, 59.49 ± 20.72, 54.79 ± 46.59, 48.95 ± 39.84, respectively(p=0.169). There were no significant differences in each treatment group bacterial colonization(p>0.05). There were no significant correlation between bacterial colonization and remaining burn surface area (p>0.05).

Conclusion

While morphologically, the wound in NPWT treatment groups appeared better in granulation and crust formation, the remaining wound surface area and the number of bacterial colonization were not significantly difference compared to standard therapy (silver sulfadiazine and NS gauze). There were no significant correlation between the amount of bacterial colonization and remaining wound surface area on every treatment group.

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Sepsis is one of cause burn injury mortality.

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NPWT is promising burn injury treatment.

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There was no significant difference of wound healing in various treatments.

Insights into Host-Pathogen Interactions in Biofilm-Infected Wounds Reveal Possibilities for New Treatment Strategies

Normal wound healing occurs in three phases—the inflammatory, the proliferative, and the remodeling phase. Chronic wounds are, for unknown reasons, arrested in the inflammatory phase. Bacterial biofilms may cause chronicity by arresting healing in the inflammatory state by mechanisms not fully understood. Pseudomonas aeruginosa, a common wound pathogen with remarkable abilities in avoiding host defense and developing microbial resistance by biofilm formation, is detrimental to wound healing in clinical studies. The host response towards P. aeruginosa biofilm-infection in chronic wounds and impact on wound healing is discussed and compared to our own results in a chronic murine wound model. The impact of P. aeruginosa biofilms can be described by determining alterations in the inflammatory response, growth factor profile, and count of leukocytes in blood. P. aeruginosa biofilms are capable of reducing the host response to the infection, despite a continuously sustained inflammatory reaction and resulting local tissue damage. A recent observation of in vivo synergism between immunomodulatory and antimicrobial S100A8/A9 and ciprofloxacin suggests its possible future therapeutic potential.

Efficacy of Antiseptic Solutions in Treatment of Staphylococcus Aureus Infected Surgical Wounds with Patches of Vascular Graft: An Experimental Study in Rats

Background and objectives: Treatment of a prosthetic vascular graft infection (PVGI) remains a challenging problem in vascular surgery. The aim of this study was to design a novel rat model for treatment of peripheral vascular prosthesis infection caused by Staphylococcus aureus (S. aureus) and to determine the efficacy of different antiseptic solutions in suppressing or eradicating infection from the wound and the graft material itself. Materials and methods: A piece of Dacron vascular prosthesis was surgically implanted at the dorsum of 48 Wistar rats and the wounds were infected with 5 McFarland standard inoculum of S. aureus. Suppurating wounds were daily irrigated with different antiseptic solutions: octenidine dihydrochloride, povidone-iodine, chlorhexidine digluconate, and sterile saline. The antimicrobial action of antiseptics was defined according to their capability to eradicate bacteria from the graft surroundings and bacteriological examination of the graft itself. Extended studies on wound microbiology, cytology, and histopathology were performed with an additional group of 10 rats, treated with the most effective antiseptic-octenidine dihydrochloride. Results: Four-day treatment course with octenidine, povidone-iodine, and chlorhexidine resulted in 99.98% (p = 0.0005), 90.73% (p = 0.002), and 65.97% (p = 0.004) decrease in S. aureus colonies in wound washouts, respectively. The number of S. aureus colonies increased insignificantly by 19.72% (p = 0.765) in control group. Seven-day treatment course with octenidine eradicated viable bacteria from nine out of 10 wound washouts and sterilized one vascular graft. Conclusions: A reproducible rat model of PVGI with a thriving S. aureus infection was designed. It is a first PVGI animal model where different antiseptic solutions were applied as daily irrigations to treat peripheral PVGI. Seven-day treatment with octenidine eradicated bacteria from the wound washouts for 90% of rats and one vascular graft. Further studies are needed to investigate if irrigations with octenidine could properly cure vascular bed from infection to assure a successful implantation of a new synthetic vascular substitute.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.

Efficacy of thermosensitive chitosan/β-glycerophosphate hydrogel loaded with β-cyclodextrin-curcumin for the treatment of cutaneous wound infection in rats

Wound infection has been a persistent problem that is common and costly. Thermosensitive hydrogel has been demonstrated to be a suitable dressing candidate due to its high moldability, easy administration and ability to maintain a moist topical environment at the wound bed. In the present study, a novel thermosensitive hydrogel was successfully prepared and characterized to have a porous inner structure and a sustained curcumin-releasing profile. The wound healing ability of the hydrogel was investigated in a wound infection model in rats. On analysis, it was observed that the hydrogel complex-dressed wounds exhibited a faster wound closure rate compared with gauze-covered wounds, which was paralleled with improved histological outcomes that were observed. Additionally, the results of in vitro antimicrobial, anti-oxidant, western blot analysis and reverse transcription-quantitative polymerase chain reaction assays indicated that the hydrogel complex had distinct anti-oxidative, antimicrobial and anti-nuclear factor-κB-signaling capacities. These results suggest that this novel hydrogel may be a suitable candidate for facilitating the healing of infected cutaneous wounds in rats.

Biofilms and Wounds: An Overview of the Evidence

Significance: Microorganisms can exist both in the planktonic and biofilm state. Each phenotypic state has a role to play in delaying healing and causing infections of both acute and chronic wounds. However, the virulent biofilm state is the fundamental reason that chronic wounds do not heal in a timely manner. We hypothesize that because microorganisms attach to any surface, biofilms can be found in all chronic wounds. However, it is not the biofilm per se that represents the greatest obstacle to the healing of a chronic wound, but its virulence and pathogenicity. Recent Advances: Numerous studies with animals and humans have identified biofilms in wounds. In particular, these studies have highlighted how biofilms impede host fibroblast development, inflammatory responses, and the efficacy of antimicrobial therapy. Despite this, the role biofilms play in affecting the healing of wounds is still vigorously debated. Critical Issues: Clinicians must understand the role that pathogenic biofilms play in impairing the healing of chronic wounds and in increasing the risk for wound infection, with its potentially catastrophic outcomes. The composition of the biofilm, its physiochemical properties, the climaxed indigenous microbiota and their virulence/pathogenicity, microbial numbers and the host's pathophysiology, and immunological fitness will govern the sustainability of a pathogenic biofilm in a wound and its resistance to interventions. Future Directions: Establishing which specific pathogenic biofilms delay wound healing should help guide better wound care practices.

A double-edged sword: the role of VEGF in wound repair and chemoattraction of opportunist pathogens

Wound healing is a complex process essential to repairing damaged tissues and preventing infection. Skin is the first line of defense, a chief physical barrier to microbe entry. Wound healing is a physical rebuilding process, but at the same time it is an inflammatory event. In turn, molecules for wound repair are secreted by fibroblasts and others present at the wound site. Vascular endothelial growth factor (VEGF) is a critical cytokine that exhibits chemoattractant properties, recruiting other immune cells to the site. Although generally beneficial, VEGF may also act as a chemoattractant for invading microorganisms, such as Pseudomonas aeruginosa.P. aeruginosa is problematic during wound infection due to its propensity to form biofilms and exhibit heightened antimicrobial resistance. Here, we explored the influence of VEGF gradients (in a microfluidic device wound model) on the motility and chemotactic properties of P. aeruginosa. At lower concentrations, VEGF had little effect on motility, but as the maximal concentration within the gradient increased, P. aeruginosa cells exhibited directed movement along the gradient. Our data provide evidence that while beneficial, VEGF, in excess, may aid colonization by P. aeruginosa. This highlights the necessity for the efficient resolution of inflammation. Understanding the dynamics of wound colonization may lead to new/enhanced therapeutics to hasten recovery.

Collagen and hyaluronan at wound sites influence early polymicrobial biofilm adhesive events

BACKGROUND

Wounds can easily become chronically infected, leading to secondary health complications, which occur more frequently in individuals with diabetes, compromised immune systems, and those that have suffered severe burns. When wounds become chronically infected, biofilm producing microbes are often isolated from these sites. The presence of a biofilm at a wound site has significant negative impact on the treatment outcomes, as biofilms are characteristically recalcitrant to removal, in part due to the formation of a protective matrix that shield residents organisms from inimical forces. Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) are two of the organisms most prevalently isolated from wound sites, and are of particular concern due to their elevated levels of antibiotic resistance, rapid growth, and exotoxin production. In order to understand the biofilm forming abilities of these microbes in a simulated wound environment we used a microtiter plate assay to assess the ability of these two organisms to bind to proteins that are typically found at wound sites: collagen and hyaluronan.

RESULTS

Collagen and hyaluronan were used to coat the wells of 96-well plates in collagen:hyaluronan ratios of 0:1, 3:1, 1:1, 1:3, and 1:0 . P. aeruginosa and MRSA were inoculated as mono- and co-cultures (1:1 and a 3:1 MRSA: P. aeruginosa). We determined that coating the wells with collagen and/or hyaluronan significantly increased the biofilm biomass of attached cells compared to an uncoated control, although no one coating formulation showed a significant increase compared to any other combination. We also noted that the fold-change increase for MRSA upon coating was greater than for P. aeruginosa.

CONCLUSIONS

Our study suggests that the presence of collagen and/or hyaluronan at wound sites may be an important factor that influences the attachment and subsequent biofilm formation of notorious biofilm-formers, such as MRSA and P. aeruginosa. Understanding the kinetics of binding may aid in our comprehension of recalcitrant wound infection development, better enabling our ability to design therapies that would prevent or mitigate the negative outcomes associated with such infections.