Microscopy visualisation confirms multi-species biofilms are ubiquitous in diabetic foot ulcers

An in vitro collagen perfusion wound biofilm model; with applications for antimicrobial studies and microbial metabolomics

Background

The majority of in vitro studies of medically relevant biofilms involve the development of biofilm on an inanimate solid surface. However, infection in vivo consists of biofilm growth on, or suspended within, the semi-solid matrix of the tissue, whereby current models do not effectively simulate the nature of the in vivo environment. This paper describes development of an in vitro method for culturing wound associated microorganisms in a system that combines a semi-solid collagen gel matrix with continuous flow of simulated wound fluid. This enables culture of wound associated reproducible steady state biofilms under conditions that more closely simulate the dynamic wound environment. To demonstrate the use of this model the antimicrobial kinetics of ceftazidime, against both mature and developing Pseudomonas aeruginosa biofilms, was assessed. In addition, we have shown the potential application of this model system for investigating microbial metabolomics by employing selected ion flow tube mass spectrometry (SIFT-MS) to monitor ammonia and hydrogen cyanide production by Pseudomonas aeruginosa biofilms in real-time.

Results

The collagen wound biofilm model facilitates growth of steady-state reproducible Pseudomonas aeruginosa biofilms under wound like conditions. A maximum biofilm density of 10¹⁰ cfu slide^− 1 was achieved by 30 h of continuous culture and maintained throughout the remainder of the experiment. Treatment with ceftazidime at a clinically relevant dose resulted in a 1.2–1.6 log reduction in biofilm density at 72 h compared to untreated controls. Treatment resulted in loss of complex biofilm architecture and morphological changes to bacterial cells, visualised using confocal microscopy. When monitoring the biofilms using SIFT-MS, ammonia and hydrogen cyanide levels peaked at 12 h at 2273 ppb (±826.4) and 138 ppb (±49.1) respectively and were detectable throughout experimentation.

Conclusions

The collagen wound biofilm model has been developed to facilitate growth of reproducible biofilms under wound-like conditions. We have successfully used this method to: (1) evaluate antimicrobial efficacy and kinetics, clearly demonstrating the development of antimicrobial tolerance in biofilm cultures; (2) characterise volatile metabolite production by P. aeruginosa biofilms, demonstrating the potential use of this method in metabolomics studies.

Effect on total microbial load and community composition with two vs six-week topical Cadexomer Iodine for treating chronic biofilm infections in diabetic foot ulcers

This study compares two vs six weeks of topical antimicrobial therapy with Cadexomer Iodine in patients with diabetic foot ulcers (DFUs) complicated by chronic biofilm infections. Patients with non-healing DFUs with suspected chronic biofilm infections were eligible for enrolment. Patients were randomised to receive either two or six weeks of treatment with topical Cadexomer Iodine. Tissue biopsies from the ulcers were obtained pre-and-post treatment and underwent DNA sequencing and real-time quantitative polymerase chain reaction (PCR) to determine the total microbial load, community composition, and diversity of bacteria. Scanning electron microscopy confirmed biofilm in all 18 ulcers with suspected chronic biofilm infections. Cadexomer Iodine resulted in 14 of 18 (78%) samples achieving a mean 0.5 log10 reduction in microbial load. Regardless of treatment duration, there was no statistical difference in the reduction of total microbial loads. No difference in the rate of wound healing in the two groups was seen at 6 weeks. Cadexomer Iodine reduces the total microbial load in DFUs with chronic biofilm infections and affects microbial community composition and diversity. All ulcers in both groups showed an initial reduction in wound size with application of Cadexomer Iodine, which might reflect its effect on biofilms.

Biofilm management using monofilament fibre debridement technology: outcomes and clinician and patient satisfaction

Objective:

Best practice in wound bed preparation and biofilm-based wound management includes debridement to create a clean wound bed and to assist in minimising the redevelopment of biofilm. Biofilm that is not removed inhibits healing and redevelops if not prevented from doing so with topical antimicrobial agents. Monofilament fibre debriding technology (MFDT) is used for effective and rapid mechanical debridement of loose material, slough and biofilm. The objective of this evaluation was to determine the clinical effect and consequential levels of health professional and patient satisfaction with the results of a biofilm pathway that included MFDT to achieve debridement.

Methods:

This non-comparative, open label evaluation was conducted in static and non-static wounds that required debridement. MFDT was used to debride in a two-week evaluation of a biofilm pathway. Wounds were debrided three times in week one and twice in week two. Each debridement was followed by treatment with an antimicrobial dressing. Other care included secondary dressings and compression delivered according to local practice, guidelines and formularies. After the clinical evaluation, health professionals were invited to complete an online survey of the clinical outcomes and their satisfaction with the biofilm pathway.

Results:

There were 706 health professionals who provided answers to the survey questions. Wound types evaluated were leg ulcers (67.4%), pressure ulcers (10%), dehisced surgical wounds (1.7%), diabetic foot ulcers (7.4%) and other wounds (13.4%). Of the wounds, 9% were reported as non-static despite the eligibility criteria. Not all wounds followed the pathway. The most frequently-used antimicrobial was silver. Non-antimicrobial products used included all-in-one dressings, other secondary dressings and compression. There was a change in 77% of wounds overall after two weeks. Change was reported almost equally for both static and non-static wounds. Health professionals who did or did not follow the pathway were ‘completely satisfied’ or ‘satisfied’ with the overall clinical outcome 96% and 95%, respectively. Of the patients, 77% were ‘completely satisfied’ or ‘satisfied’ with healing after following the pathway, as reported by the treating health professional.

Conclusion:

The biofilm pathway that includes MFDT appears effective. Wounds managed on the pathway were debrided effectively and healing progressed to the satisfaction of both health professionals and patients.

Rapid debridement with monofilament fibre debridement technology: clinical outcomes and practitioner satisfaction

Objective:

To determine the clinical effect and consequential levels of health professionals and patient satisfaction with the results of debridement episodes of wounds with visible slough and/or scaly skin using monofilament fibre debridement technology.

Methods:

This was a non-comparative, open label evaluation conducted in static/non-healing acute and chronic wounds with visible slough and/or scaly skin that required debridement. Monofilament fibre debridement technology was applied in 1–2 sequential treatment episodes during normal clinical practice which followed local practice, guidelines or formularies. Following the clinical phase of the evaluation, health professionals were invited to complete an online survey of the clinical outcomes and their satisfaction with them.

Results:

Survey questions were answered by 1129 health professionals. Wounds managed using the monofilament fibre debridement technology during this evaluation included leg ulcers (63%), pressure ulcers (10%), dehisced surgical wounds (3%), diabetic foot ulcers (8%) and other wounds (13%). ‘Other’ wound types included acute dirty wounds, burns, cellulitis, psoriasis, diabetic amputation wounds, dry flaky skin, moisture wounds, trauma, varicose eczema. Of the wounds, 12% were reported as non-static. There was visible change in the wound and/or skin after first use of the monofilament fibre debridement technology in a high proportion of all wound types, and a further increase in the proportion of wounds with visible change after the second use. The visible difference was significant for both static and non-static wounds. User and patient satisfaction with all clinical outcomes were high, whether or not the user and patient had previous experience of monofilament fibre debridement technology.

Conclusion:

Monofilament fibre debridement technology provides rapid, visible and effective debridement of slough and scaly skin after one application and further visible improvement after two applications in static and non-static wounds. Health professionals and patients report high levels of satisfaction with outcomes following application of the monofilament fibre debridement technology.

Diabetic foot infection: A critical complication

The number of people in the world with diabetes has nearly quadrupled in the past 40 years. Current data show that 25% of these diabetics will develop a foot ulcer in their lifetime and that the cost of care for a diabetic foot ulcer (DFU) is over twice that of any other chronic ulcer aetiology. Microbial biofilm has been linked to both wound chronicity and infection. Close to 1 in 2 diabetics with a DFU are predicted to go on to develop a diabetic foot infection (DFI). The majority of these DFIs have been found to evolve even before the diabetic individual has received an initial referral for expert DFU management. Of these infected DFUs, less than half have been shown to heal over the next year; many of these individuals will require costly hospitalisation, and current data show that far too many DFIs will require extremity amputation to achieve infection resolution. The development of an infection in a DFU is critical at least in part because paradigms of infection prevention and management are evolving. The effectiveness of our current practice standards is being challenged by a growing body of research related to the prevalence and recalcitrance of the microbes in biofilm to topical and systemic antimicrobials. This article will review the magnitude of current challenges related to DFI prevention and management along with what is currently considered to be standard of care. These ideas will be compared and contrasted with what is known about the biofilm phenotype; then, considerations to support progress towards the development of more cost-effective protocols of care are highlighted.

The role of the microbiome in nonhealing diabetic wounds

Wound healing is a highly coordinated and complex process, and there can be devastating consequences if it is interrupted. It is believed that, in combination with host factors, microorganisms in a wound bed can not only impair wound healing but can lead to stalled, chronic wounds. It is hypothesized that the wound microbiota persists in chronic wounds as a biofilm, recalcitrant to antibiotic and mechanical intervention. Cultivation-based methods are the gold standard for identification of pathogens residing in wounds. However, these methods are biased against fastidious organisms, and do not capture the full extent of microbial diversity in chronic wounds. Thus, the link between specific microbes and impaired healing remains tenuous. This is partially because local infection and, more specifically, the formation of a biofilm, is difficult to diagnose. This has led to research efforts aimed at understanding if biofilm formation delays healing and leads to persistent and chronic infection. Circumventing challenges associated with culture-based estimations, advances in high-throughput sequencing analysis has revealed that chronic wounds are host to complex, diverse microbiomes comprising multiple species of bacteria and fungi. Here, we discuss how the use of genomic methodologies to study wound microbiomes has advanced the current understanding of infection and biofilm formation in chronic wounds.

Role of anaerobes in polymicrobial communities and biofilms complicating diabetic foot ulcers

Infected tissues in the feet of people with diabetes in the form of a diabetic foot ulcer (DFU) present a complex pathology for clinicians to manage. This is partly attributed to the multi-factorial nature of the disease, which may include; altered foot architecture leading to excessive plantar pressures and frictional forces peripheral arterial disease and loss of protective sensation. In addition, to the above co-morbid variables, it is understood that a delayed wound healing state may be perpetuated by the presence of microorganisms residing in the wound tissue. The microbiology of chronic DFUs has often been reported as being polymicrobial. Of growing interest is the presence and potential role of anaerobic microorganisms in the pathology of DFUs and how they may contribute to the infective process or delayed healing. The presence of anaerobes in DFUs has been greatly underestimated, largely due to the limitations of conventional culture methods in identifying them from samples. Advancements in molecular and microscopy techniques have extended our view of the wound microbiome in addition to observing the growth and behaviour (planktonic or biofilm) of microorganisms in situ. This review paper will reflect on the evidence for the role and significance of anaerobes in DFUs and infection. A focus of this review will be to explore recent advancements in molecular genomics and microscopy techniques in order to better assess the roles of anaerobic bacteria in chronic DFUs and in biofilm-based wound care.

Understanding the microbiome of diabetic foot osteomyelitis: insights from molecular and microscopic approaches

OBJECTIVES

Rigorous visual evidence on whether or not biofilms are involved in diabetic foot osteomyelitis (DFO) is lacking. We employed a suite of molecular and microscopic approaches to investigate the microbiome, and phenotypic state of microorganisms involved in DFO.

METHODS

In 20 consecutive subjects with suspected DFO, we collected intraoperative bone specimens. To explore the microbial diversity present in infected bone we performed next generation DNA sequencing. We used scanning electron microscopy (SEM) and peptide nucleic acid fluorescent in situ hybridization (PNA-FISH) with confocal microscopy to visualize and confirm the presence of biofilms.

RESULTS

In 19 of 20 (95%) studied patients presenting with DFO, it was associated with an infected diabetic foot ulcer. By DNA sequencing of infected bone, Corynebacterium sp. was the most commonly identified microorganism, followed by Finegoldia sp., Staphylococcus sp., Streptococcus sp., Porphyromonas sp., and Anaerococcus sp. Six of 20 bone samples (30%) contained only one or two pathogens, while the remaining 14 (70%) had polymicrobial communities. Using a combination of SEM and PNA-FISH, we identified microbial aggregates in biofilms in 16 (80%) bone specimens and found that they were typically coccoid or rod-shaped aggregates.

CONCLUSIONS

The presence of biofilms in DFO may explain why non-surgical treatment of DFO, relying on systemic antibiotic therapy, may not resolve some chronic infections caused by biofilm-producing strains.

Association between biofilm and multi/extensive drug resistance in diabetic foot infection

PURPOSE

We aimed to determine significant risk factors for biofilm production and to investigate the association between antimicrobial resistance profile and biofilm formation in the bacterial isolates obtained from patients with diabetic foot infection (DFI).

METHODS

Demographic, clinical, laboratory and outcome data of 165 patients, prospectively recorded and followed between January 2008 and December 2015 by a multidisciplinary committee, were analysed. Standard microbiological methods were adopted. Risk factors associated with biofilm were determined by univariate and multivariate analyses.

RESULTS

The overall rate of biofilm production among 339 wound isolates was 34%. The biofilm production rate was significantly higher in Gram-negative micro-organisms (39%) in comparison with Gram positives (21%) (P = .01). A. baumannii presented the highest biofilm production (62%), followed by P. aeruginosa (52%) and Klebsiella spp. (40%). On univariate analysis, significant factors associated with biofilm were antibiotic use within last 3 months (OR:2.94, CI: 1.5-5.75, P = .002), recurrent DFI within last 6 months (OR:2.35, CI: 1.23-4.53, P = .01), hospitalisation within last 3 months due to ipsilateral recurrent DFI (OR:2.44, CI: 1.06-5.58, P = .03), presence of amputation history (OR: 2.20, CI: 1.14-4.24, P = .01), multidrug-resistant (MDR) micro-organism (OR: 7.76, CI: 4.53-13.35, P<.001) and extensively drug-resistant (XDR) micro-organism (OR:11.33, CI:4.97-26.55, P<.001). Multivariate regression analysis revealed two variables to be significant factors associated with biofilm: MDR micro-organism (OR: 3.63, CI: 1.58-8.33, P = .002) and XDR micro-organism (OR:4.06, CI: 1.25-13.1, P = .01).

CONCLUSIONS

Multi/extensive drug resistance and previous recurrent DFIs were significantly associated with biofilm formation in patients with diabetic foot.

Consensus guidelines for the identification and treatment of biofilms in chronic nonhealing wounds

BACKGROUND

Despite a growing consensus that biofilms contribute to a delay in the healing of chronic wounds, conflicting evidence pertaining to their identification and management can lead to uncertainty regarding treatment. This, in part, has been driven by reliance on in vitro data or animal models, which may not directly correlate to clinical evidence on the importance of biofilms. Limited data presented in human studies have further contributed to the uncertainty. Guidelines for care of chronic wounds with a focus on biofilms are needed to help aid the identification and management of biofilms, providing a clinical focus to support clinicians in improving patient care through evidence-based medicine.

METHODS

A Global Wound Biofilm Expert Panel, comprising 10 clinicians and researchers with expertise in laboratory and clinical aspects of biofilms, was identified and convened. A modified Delphi process, based on published scientific data and expert opinion, was used to develop consensus statements that could help identify and treat biofilms as part of the management of chronic nonhealing wounds. Using an electronic survey, panel members rated their agreement with statements about biofilm identification and treatment, and the management of chronic nonhealing wounds. Final consensus statements were agreed on in a face-to-face meeting.

RESULTS

Participants reached consensus on 61 statements in the following topic areas: understanding biofilms and the problems they cause clinicians; current diagnostic options; clinical indicators of biofilms; future options for diagnostic tests; treatment strategies; mechanical debridement; topical antiseptics; screening antibiofilm agents; and levels of evidence when choosing antibiofilm treatments.

CONCLUSION

This consensus document attempts to clarify misunderstandings about the role of biofilms in clinical practice, and provides a basis for clinicians to recognize biofilms in chronic nonhealing wounds and manage patients optimally. A new paradigm for wound care, based on a stepped-down treatment approach, was derived from the consensus statements.