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

The role of the skin microbiome in wound healing

The efficient management of skin wounds for rapid and scarless healing represents a major clinical unmet need. Nonhealing skin wounds and undesired scar formation impair quality of life and result in high healthcare expenditure worldwide. The skin-colonizing microbiota contributes to maintaining an intact skin barrier in homeostasis, but it also participates in the pathogenesis of many skin disorders, including aberrant wound healing, in many respects. This review focuses on the composition of the skin microbiome in cutaneous wounds of different types (i.e. acute and chronic) and with different outcomes (i.e. nonhealing and hypertrophic scarring), mainly based on next-generation sequencing analyses; furthermore, we discuss the mechanistic insights into host-microbe and microbe-microbe interactions during wound healing. Finally, we highlight potential therapeutic strategies that target the skin microbiome to improve healing outcomes.

Deferiprone-Gallium-Protoporphyrin Chitogel Decreases Pseudomonas aeruginosa Biofilm Infection without Impairing Wound Healing

Pseudomonas aeruginosa is one of the most common pathogens encountered in clinical wound infections. Clinical studies have shown that P. aeruginosa infection results in a larger wound area, inhibiting healing, and a high prevalence of antimicrobial resistance. Hydroxypyridinone-derived iron chelator Deferiprone (Def) and heme analogue Gallium-Protoporphyrin (GaPP) in a chitosan-dextran hydrogel (Chitogel) have previously been demonstrated to be effective against PAO1 and clinical isolates of P. aeruginosa in vitro. Moreover, this combination of these two agents has been shown to improve sinus surgery outcomes by quickly reducing bleeding and preventing adhesions. In this study, the efficacy of Def-GaPP Chitogel was investigated in a P. aeruginosa biofilm-infected wound murine model over 6 days. Two concentrations of Def-GaPP Chitogel were investigated: Def-GaPP high dose (10 mM Def + 500 µg/mL GaPP) and Def-GaPP low dose (5 mM Def + 200 µg/mL GaPP). The high-dose Def-GaPP treatment reduced bacterial burden in vivo from day 2, without delaying wound closure. Additionally, Def-GaPP treatment decreased wound inflammation, as demonstrated by reduced neutrophil infiltration and increased anti-inflammatory M2 macrophage presence within the wound bed to drive wound healing progression. Def-GaPP Chitogel treatment shows promising potential in reducing P. aeruginosa cutaneous infection with positive effects observed in the progression of wound healing.

Wound Debridement in Pyoderma Gangrenosum

BACKGROUND

Wound debridement improves healing in a variety of acute and chronic ulcers. However, there is concern that debridement may trigger pathergy and worsen pyoderma gangrenosum (PG).

OBJECTIVE

To determine whether published evidence supports conservative wound debridement for PG.

DATA SOURCES

The authors reviewed the literature published in MEDLINE through January 2023 using the search germs "pyoderma gangrenosum" and "debridement."

STUDY SELECTION

Articles reporting sharp surgical debridement or maggot debridement for PG were included in the review. The authors also searched the reference sections of the reviewed articles for additional reports on debridement for PG.

DATA EXTRACTION

Clinical data regarding patient status, procedures performed, and patient outcomes were extracted from the selected articles.

DATA SYNTHESIS

There are multiple reports of uncontrolled, active-phase PG wounds worsening after aggressive excisional debridement of viable inflamed tissues. In contrast, there is no evidence indicating that conservative debridement of nonviable necrotic tissue worsens PG wounds, regardless of the disease activity. There are multiple reports of successful debridement and surgical grafting for PG in remission.

CONCLUSIONS

There is no evidence in favor of or against using conservative debridement of nonviable necrotic tissue for a PG wound. Therefore, it should not be considered contraindicated, even in the active phase of the disease.

Association Between the Diabetic Foot Ulcer and the Bacterial Colony of the Skin Based on 16S rRNA Gene Sequencing: An Observational Study

Objective

Microorganisms have been the main cause of refractory and high recurrence of diabetic foot ulcer (DFU). This study attempted to observe the skin bacterial colony in healthy skin, diabetic skin and DFU skin.

Methods

Forty-eight diabetes patients were recruited at Panyu Central Hospital from March 2021 to March 2022 and divided into DFU group (T group, n = 22), diabetes without foot ulcer group (TW group, n = 26). Besides, a healthy control group (H group, n = 10) was recruited at the same time. The swab samples of foot skin in the same position in the three groups were collected. The microorganisms obtained from the skin were analyzed by 16S rRNA gene sequencing. The composition of the skin microorganisms was determined, and the species diversity of the skin microbiota was analyzed by α and β diversity. The species differences in the skin microbiota and the relative abundance of different operational taxonomic units (OUTs) with the most significant abundance were analyzed by linear discriminant analysis effect size (LEfSe).

Results

Significant changes were found in the composition of the skin microbiota in the T and TW groups relative to the H group. However, the species diversity of the skin microbiota was significantly reduced in the T and TW groups, with the lowest one in the T group. The composition of microbial diversity in the T group was significantly different from that of the TW and H groups. Among the skin bacterial colonies, the abundance of Staphylococcus, Enhydrobacter, and Corynebacterium_1 was obviously reduced, while that of Escherichia coli and Pseudomonas was significantly increased.

Conclusion

Changes in the abundance of Staphylococcus, Enhydrobacter, Corynebacterium_1, Escherichia coli and Pseudomonas in the skin bacterial colonies can be the main causative factors for DFU. This study indicates that altering the microbiota composition of wounds may help the treatment of DFU.

Murine burn lesion model for studying acute and chronic wound infections

Acute wounds, such as thermal injury, and chronic wounds are challenging for patients and the healthcare system around the world. Thermal injury of considerable size induces immunosuppression, which renders the patient susceptible to wound infections, but also in other foci like the airways and urinary tract. Infected thermal lesions can progress to chronic wounds with biofilm making them more difficult to treat. While animal models have their limitations, murine wound models are still the best tool at the moment to identify strategies to overcome these challenges. Here, we present a murine burn model, which has been developed to study biofilm formation, the significance of wound healing, and for identifying novel treatment candidates. Investigating the effect of a thermal injury in mice, we observed that 48 h after introduction of the injury, the mice showed a reduction in polymorphonuclear neutrophil granulocytes (PMNs) and a reduced capacity for phagocytosis and oxidative burst. Regarding the chronic wound, Pseudomonas aeruginosa biofilm arrested wound healing and kept the wound in an inflammatory state, but suppressing PMN function by means of the PMN factor S100A8/A9, corresponding to observations in human venous leg ulcers. Monotherapy and dual treatment with S100A8/A9 and ciprofloxacin on P. aeruginosa biofilm-infected murine wounds have been investigated. In combination, S100A8/A9 and ciprofloxacin reduced the bacterial quantity, lowered the proinflammatory response, and increased anti-inflammatory cytokines after 4 days of treatment. When the treatment was prolonged, an additional prevention of resistance development was detected in all the dual-treated mice. In the present review, we provide data on using the murine model for research with the aim of better understanding pathophysiology of wounds and for identifying novel treatments for humans suffering from these lesions.

Histopathological role of vitamin D deficiency in recurrent/chronic tonsillitis pathogenesis: Vascular epithelial growth factor-mediated angiogenesis in tonsil

Objectives

Our aim in this study is to reveal the role of vitamin D deficiency in the pathogenesis of recurrent/chronic tonsillitis and to determine the expression of vascular epithelial growth factor (VEGF).

Material and Methods

This study was conducted between September and February. Thirty‐two patients between the ages of 3 and 35 (mean age 9.71) with recurrent episodes of chronic tonsillitis were selected. Patients were divided into four groups according to their 25OHD levels. Patients with 25OHD levels 0–10 ng/ml were determined as Group 1, 11–20 ng/ml Group 2, 21–30 ng/ml Group 3, and 31–50 ng/ml control Group 4. Routine histological tissue sampling was performed for histopathological evaluation of the tonsillar tissues under light microscope (LM). Five micron sections were taken from the paraffin blocks and stained with Hematoxylin Eosin (HE) and Trichrome Masson (TCM). VEGF expression was examined immunohistochemically for each group.

Results

Our analysis showed VEGF expression in all study groups (32 tonsillar tissues). Group 1 and Group 2 histopathological scores were significantly higher than the other groups (p < .001). There were significant differences in VEGF expressions between the four groups (p < .001). 25OHD levels of the patients in Groups 1 and 2 with strong VEGF expression were significantly lower than the other groups (p < .001).

Conclusions

In conclusion, this study showed an increased angiogenesis in tonsil and an increase in VEGF expression of the tonsillar surface epithelium when blood serum 25OHD levels <20 ng/ml.

Neuropeptides, Inflammation, Biofilms, and diabetic Foot Ulcers

A diabetic foot ulcer (DFU) is a serious complication in patients with diabetes mellitus (DM). A DFU is the most common cause of non-traumatic limb amputation, and patients with DFUs have increased mortality rates within 5 years after amputation. DFUs also increase the risk of cardiovascular and cerebrovascular diseases; therefore, with the increasing incidence and prevalence of diabetic foot wounds, DFUs are gradually becoming a major public health problem. The pathophysiology of DFUs is complicated and remains unclear. In recent years, many studies have demonstrated that the pathophysiology of DFUs is especially associated with neuropeptides, inflammation, and biofilms. Neuropeptides, especially substance P (SP) and calcitonin gene-related peptide (CGRP), play an important role in wound healing. SP and CGRP accelerate the healing of cutaneous wounds by promoting neovascularization, inhibiting the release of certain proinflammatory chemokines, regulating macrophage polarization, and so on. However, the expression of SP and CGRP was downregulated in DM and DFUs. DFUs are characterized by a sustained inflammatory phase. Immune cells such as neutrophils and macrophages are involved in the sustained inflammatory phase in DFUs by extracellular traps (NETs) and dysregulated macrophage polarization, which delays wound healing. Furthermore, DFUs are at increased risk of biofilm formation. Biofilms disturb wound healing by inducing a chronic inflammatory response, inhibiting macrophage phagocytosis and keratinocyte proliferation migration, and transferring antimicrobial resistance genes. To understand the relationships among neuropeptides, inflammation, biofilms, and DFUs, this review highlights the recent scientific advances that provide possible pathophysiological insights into the delayed healing of DFUs.

Biofilm-Innate Immune Interface: Contribution to Chronic Wound Formation

Delayed wound healing can cause significant issues for immobile and ageing individuals as well as those living with co-morbid conditions such as diabetes, cardiovascular disease, and cancer. These delays increase a patient’s risk for infection and, in severe cases, can result in the formation of chronic, non-healing ulcers (e.g., diabetic foot ulcers, surgical site infections, pressure ulcers and venous leg ulcers). Chronic wounds are very difficult and expensive to treat and there is an urgent need to develop more effective therapeutics that restore healing processes. Sustained innate immune activation and inflammation are common features observed across most chronic wound types. However, the factors driving this activation remain incompletely understood. Emerging evidence suggests that the composition and structure of the wound microbiome may play a central role in driving this dysregulated activation but the cellular and molecular mechanisms underlying these processes require further investigation. In this review, we will discuss the current literature on: 1) how bacterial populations and biofilms contribute to chronic wound formation, 2) the role of bacteria and biofilms in driving dysfunctional innate immune responses in chronic wounds, and 3) therapeutics currently available (or underdevelopment) that target bacteria-innate immune interactions to improve healing. We will also discuss potential issues in studying the complexity of immune-biofilm interactions in chronic wounds and explore future areas of investigation for the field.

Development of nanosilver doped carboxymethyl chitosan-polyamideamine alginate composite dressing for wound treatment

Nowadays, treatment to the infected wounds caused by bacterial even multi-resistant bacterial strains and subsequently complete skin regeneration remain a critical clinical challenge. Herein, a novel multi-functional platform (Alg/1.0Ag@CMC-PAMAM/PRP) was prepared as wound dressings by mixing platelet rich plasma (PRP) with the sodium alginate (Alg) based dressing containing nano silver (Ag)-doped carboxymethyl chitosan grafted polyamideamine (Ag@CMC-PAMAM) cationic polymers. The present dressings exhibited high swelling, suitable water vapor transmission rate (WVTR), and good mechanical properties and degradability, as well as sustained release of PRP. Besides, the component of Ag@CMC-PAMAM nanoparticles endow them with excellent antibacterial performance, while the incorporation of PRP promotes the effect of anti-inflammatory and angiogenesis by up-regulating relative activity factor expression of TGF-β1, CD31 and α-SMA and down-regulating the inflammatory-relative genes including TNF-α, IL-6 and IL-1β, all of which promote the closure of wound and produce a superior healing effect to the commercial Aquacel Ag group. This work indicates that the prepared Alg/1.0Ag@CMC-PAMAM/PRP wound dressing is a promising biomaterial with synergistic effect of antibacterial property and wound healing.

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.

Formation of Pseudomonas aeruginosa Biofilms in Full-thickness Scald Burn Wounds in Rats

Using Sprague-Dawley rats (350-450 g; n = 61) and the recently updated Walker-Mason rat scald burn model, we demonstrated that Pseudomonas aeruginosa readily formed biofilms within full-thickness burn wounds. Following the burn, wounds were surface-inoculated with P. aeruginosa in phosphate-buffered saline (PBS), while sterile PBS was used for controls. On post-burn days 1, 3, 7, and 11, animals were euthanized and samples collected for quantitative bacteriology, bacterial gene expression, complete blood cell counts, histology, and myeloperoxidase activity. Robust biofilm infections developed in the full-thickness burn wounds inoculated with 1 × 10⁴ CFU of P. aeruginosa. Both histology and scanning electron microscopy showed the pathogen throughout the histologic cross-sections of burned skin. Quantigene analysis revealed significant upregulation of alginate and pellicle biofilm matrix genes of P. aeruginosa within the burn eschar. Additionally, expression of P. aeruginosa proteases and siderophores increased significantly in the burn wound environment. Interestingly, the host's neutrophil response to the pathogen was not elevated in either the eschar or circulating blood when compared to the control burn. This new full-thickness burn biofilm infection model will be used to test new anti-biofilm therapies that may be deployed with soldiers in combat for immediate use at the site of burn injury on the battlefield.

Insulin treatment enhances pseudomonas aeruginosa biofilm formation by increasing intracellular cyclic di-GMP levels, leading to chronic wound infection and delayed wound healing

Diabetes-related infections have become challenging and important public health problems in China and around the world. P. aeruginosa plays an important role in diabetic foot infections. As a gram-negative opportunistic pathogen, P. aeruginosa causes recurrent and refractory infections that are characterized by biofilm formation. Previous studies have demonstrated that biofilm-challenged wounds typically take longer to heal than non-biofilm-challenged normal wounds in diabetic mouse models. In the present study, we sought to explore the mechanism via which insulin treatment affects cyclic di-GMP signaling in P. aeruginosa-infected chronic wounds in db/db diabetic mice. We found that the wounds of diabetic mice healed more slowly than those of nondiabetic mice. Moreover, wound healing in diabetic mice treated with insulin exhibited a considerable delay. Peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH) was used to detect biofilms on P. aeruginosa-infected wound tissues. Increased intracellular c-di-GMP levels promoted biofilm formation in wound tissues from nondiabetic mice. Greater biofilm formation was observed in the wounds of insulin-treated diabetic mice than in the wounds of untreated diabetic mice or nondiabetic mice, in both the PAO1/p_lac-yhjH- and PAO1-infected groups. Quantitative RT-PCR indicated that upon infection with PAO1/P_lac-yhjH (the low c-di-GMP expression strain), the expression of IL-4 RNA was significantly higher in diabetic mice treated with insulin than in untreated diabetic mice or nondiabetic mice at each observation time point. Peak expression of IFN-γ occurred earlier in diabetic mice treated with insulin than in untreated diabetic mice with each of the experimental strains. Finally, P. aeruginosa harboring the plasmid pCdrA: gfp ^s was used as a reporter strain to monitor c-di-GMP levels. We found that insulin could promote biofilm formation by increasing intracellular c-di-GMP levels in vitro. Taken together, these data demonstrate that insulin treatment increases intracellular c-di-GMP levels, promotes biofilm formation and prolongs the inflammation period during the healing of infected wounds, resulting in delayed wound healing.