Investigating the humoral immune response in chronic venous leg ulcer patients colonised with Pseudomonas aeruginosa

Associations Among Wound-Related Factors Including Biofilm, Wound-Related Symptoms and Systemic Inflammation in Older Adults with Chronic Venous Leg Ulcers

Objective: The purposes of this observational prospective study were to (1) characterize the wound-related factors (wound area, the presence of biofilm, and total bacteria), wound-related symptoms (fatigue, pain, exudate, itching, and edema or swelling), and systemic inflammation (level of serum C-reactive protein [CRP]), and (2) explore associations between wound-related factors, wound-related symptoms, and systemic inflammation in older individuals with chronic venous leg ulcers (CVLUs) over 8 weeks of wound treatment. Approach: A total of 117 participants who received standardized care (weekly sharp debridement) for chronic venous ulcer were enrolled. We collected clinical data every 2 weeks during the 8 weeks of the study period or until the wound was healed (if healed before 8 weeks). Associations among variables were estimated using a Bayesian approach applied to general linear mixed models. Results: Based on Bayes factor (BF) value, there was extremely strong evidence for the association of biofilm with mean total bacteria (BF >1,000). There was moderate evidence of a direct association between biofilm presence and levels of CRP (BF 4.3) and moderate evidence of direct associations between biofilm and wound-related symptoms, pain and exudate (BF 5.12, 8.49, respectively). Innovation: Wound-related symptoms and the level of systemic CRP were associated with biofilm among patients who were receiving weekly sharp debridement. Symptom severity associated with CVLUs requires assessment and management of wound-related factors and levels of inflammation in addition to symptom assessment. Conclusion: This study is the first to examine associations among biofilm, as wound-related factors, systemic inflammation, wound-related symptoms, and wound healing in clinical settings. Symptom severity, level of systemic CRP, and wound-related factors should be considered as well as assessment of biofilm in CVLU in older individuals with CVLU.

Effect of Pseudomonas colonisation on lower limb venous ulcer healing: a systematic review

OBJECTIVE

Pseudomonas aeruginosa is a Gram-negative bacillus that commonly colonises lower limb venous ulcers. Its effects on venous ulcer healing are widely debated. It produces exotoxins and elastase, as well as forming biofilms in hard-to-heal wounds. It is postulated that these virulence factors lead to slower healing times in patients with lower limb venous ulcers colonised with Pseudomonas. This review aimed to summarise the available evidence pertaining to this topic.

METHOD

A systematic review was performed in August 2019, where the Pubmed, Cochrane and Embase databases were searched for relevant literature according to PRISMA guidelines. Retrospective and prospective studies examining the effect of Pseudomonas colonisation on any measure of ulcer healing were included.

RESULTS

Some 282 articles were screened, of which seven studies including 491 patients were ultimately included for analysis. Of these, no study demonstrated a significant association between Pseudomonas colonisation and delayed healing of venous ulcers. In five of the seven studies, the effect of Pseudomonas aeruginosa on initial ulcer size at presentation was recorded.

CONCLUSION

All the studies demonstrated an association between ulcer size and the presence of Pseudomonas aeruginosa. While Pseudomonas aeruginosa may colonise larger ulcers or those with a worse prognosis, no evidence was found to support the hypothesis that this colonisation had a negative impact on lower limb venous ulcer healing.

Skin and muscle permeating antibacterial nanoparticles for treating Staphylococcus aureus infected wounds

Majority of the chronic wounds are infected with bacteria like Staphylococcus aureus (S. aureus). The deep tissue infections are difficult to treat using topical antibiotics, due to their poor tissue penetration. In order to treat S. aureus deep tissue infections we have developed an antibiotic delivery system using chitosan nanoparticles (CNPs). To enhance their tissue penetration these CNPs were further coated using lecithin (CLNPs). Antibiotic tigecycline was loaded into chitosan nanoparticles (tCNPs) and then coated with lecithin to generate lecithin coated tigecycline loaded chitosan nanoparticles (tCLNPs). The prepared nanoparticles were characterized using DLS, SEM, TEM and FT-IR. The prepared CNPs, tCNPs, CLNPs and tCLNPs have the size range of 85 ± 10, 90 ± 18, 188 ± 5 and 235 ± 20 nm, respectively. The tCLNPs shows more sustained release pattern of tigecycline. The antibacterial activity of the developed nanoparticles was confirmed against laboratory and clinical strains of S. aureus using in vitro and ex vivo experiments. The ex vivo skin and muscle permeation study ensures the enhanced delivery of tigecycline to the deeper tissue. The prepared nanoparticles were hemo-compatible and cyto-compatible. Our study suggests that the prepared tCLNPs can be effectively used for the treatment of S. aureus infected wounds.

Bacterial spectrum colonizing chronic leg ulcers: a 10-year comparison from a German wound care center

BACKGROUND AND OBJECTIVES

Chronic wounds are colonized by many different bacteria.

PATIENTS AND METHODS

We analyzed microbiological swabs from chronic leg ulcers from 2012/2013 and matched the results with those from 2002/2003 and 2007/2008 from the same institution.

RESULTS

Results from 100 patients from our specialized wound care center were evaluated retrospectively. The etiologies were broadly variable with chronic venous insufficiency being the most common. As the most common bacterium Staphylococcus aureus was found in 53% of patients; 9% of patients were positive for methicillin-resistant S. aureus (MRSA). Pseudomonas aeruginosa was detected in 25% of patients. Different fecal bacteria and Enterobacteriaceae were found in 49% of the patients; 11% of the swabs were sterile. The detection rate for S. aureus has regressed by 17.1% over the past decade and in the case of MRSA by 12.5%. In contrast, colonization with gram-negative bacteria species significantly increased by 11.7%. This tendency was also seen in 2007/2008, but with a higher count of P. aeruginosa.

CONCLUSION

Although S. aureus is still the most frequently detected bacterium in our wound care center, there has been a shift in the bacterial spectrum from gram-positive towards gram-negative bacteria over the last decade.

Insulin treatment modulates the host immune system to enhance Pseudomonas aeruginosa wound biofilms

Diabetes affects 25.8 million people in the United States, or 8.3% of the population, and these numbers are even higher in developing countries. Diabetic patients are more susceptible to the development of chronic wounds with debilitating bacterial infections than nondiabetics. Previously, we compared the ability of the opportunistic pathogen Pseudomonas aeruginosa to cause biofilm-associated infections in chronic wounds of diabetic and nondiabetic mice (C. Watters, K. DeLeon, U. Trivedi, J. A. Griswold, M. Lyte, K. J. Hampel, M. J. Wargo, and K. P. Rumbaugh, Med. Microbiol. Immunol. 202:131-141, 2013). Unexpectedly, we observed that insulin-treated diabetic mice had significantly more biofilm in their wounds, which correlated with higher antibiotic tolerance. Here, we investigated whether insulin treatment modulates the diabetic immune system to favor P. aeruginosa biofilm formation. Utilizing a murine chronic wound model, we found that DNA protected P. aeruginosa in the wounds of insulin-treated diabetic mice from antibiotic treatment. We also observed increased numbers of neutrophils, reduced numbers of macrophages, and increased cell death in the wounds of diabetic mice on insulin therapy. Taken together, these data suggest that high levels of lysed neutrophils in the wounds of diabetic mice on insulin, combined with fewer macrophages to remove the cellular debris, contribute to increased DNA levels, which enhance P. aeruginosa biofilms.

Complement activation and inhibition in wound healing

Complement activation is needed to restore tissue injury; however, inappropriate activation of complement, as seen in chronic wounds can cause cell death and enhance inflammation, thus contributing to further injury and impaired wound healing. Therefore, attenuation of complement activation by specific inhibitors is considered as an innovative wound care strategy. Currently, the effects of several complement inhibitors, for example, the C3 inhibitor compstatin and several C1 and C5 inhibitors, are under investigation in patients with complement-mediated diseases. Although (pre)clinical research into the effects of these complement inhibitors on wound healing is limited, available data indicate that reduction of complement activation can improve wound healing. Moreover, medicine may take advantage of safe and effective agents that are produced by various microorganisms, symbionts, for example, medicinal maggots, and plants to attenuate complement activation. To conclude, for the development of new wound care strategies, (pre)clinical studies into the roles of complement and the effects of application of complement inhibitors in wound healing are required.