A rapid molecular method for characterising bacterial bioburden in chronic wounds

Characterization and mechanism of action of amphibian-derived wound-healing-promoting peptides

Wound-healing-promoting peptides are excellent candidates for developing wound-healing agents due to their small size and low production cost. Amphibians are one of the major sources of bioactive peptides, including wound-healing-promoting peptides. So far, a series of wound-healing-promoting peptides have been characterized from amphibians. We hereby summarized the amphibian-derived wound-healing-promoting peptides and their mechanism of action. Among these peptides, two peptides (tylotoin and TK-CATH) were characterized from salamanders, and twenty five peptides were characterized from frogs. These peptides generally have small sizes with 5-80 amino acid residues, nine peptides (tiger17, cathelicidin-NV, cathelicidin-DM, OM-LV20, brevinin-2Ta, brevinin-2PN, tylotoin, Bv8-AJ, and RL-QN15) have intramolecular disulfide bonds, seven peptides (temporin A, temporin B, esculentin-1a, tiger17, Pse-T2, DMS-PS2, FW-1, and FW-2) are amidated at the C-terminus, and the others are linear peptides without modifications. They all efficiently accelerated the healing of skin wounds or photodamage in mice or rats. They selectively promoted the proliferation and migration of keratinocytes and fibroblasts, recruited neutrophils and macrophages to wounds, and regulated the immune response of neutrophils and macrophages in wounds, which were essential for wound healing. Interestingly, MSI-1, Pse-T2, cathelicidin-DM, brevinin-2Ta, brevinin-2PN, and DMS-PS2 were just antimicrobial peptides, but they also significantly promoted the healing of infected wounds by clearing off bacteria. Considering the small size, high efficiency, and definite mechanism, amphibian-derived wound-healing-promoting peptides might be excellent candidates for developing novel wound-healing-promoting agents in future.

A Host-Directed Approach to the Detection of Infection in Hard-to-Heal Wounds

Wound infection is traditionally defined primarily by visual clinical signs, and secondarily by microbiological analysis of wound samples. However, these approaches have serious limitations in determining wound infection status, particularly in early phases or complex, chronic, hard-to-heal wounds. Early or predictive patient-derived biomarkers of wound infection would enable more timely and appropriate intervention. The observation that immune activation is one of the earliest responses to pathogen activity suggests that immune markers may indicate wound infection earlier and more reliably than by investigating potential pathogens themselves. One of the earliest immune responses is that of the innate immune cells (neutrophils) that are recruited to sites of infection by signals associated with cell damage. During acute infection, the neutrophils produce oxygen radicals and enzymes that either directly or indirectly destroy invading pathogens. These granular enzymes vary with cell type but include elastase, myeloperoxidase, lysozyme, and cathepsin G. Various clinical studies have demonstrated that collectively, these enzymes, are sensitive and reliable markers of both early-onset phases and established infections. The detection of innate immune cell enzymes in hard-to-heal wounds at point of care offers a new, simple, and effective approach to determining wound infection status and may offer significant advantages over uncertainties associated with clinical judgement, and the questionable value of wound microbiology. Additionally, by facilitating the detection of early wound infection, prompt, local wound hygiene interventions will likely enhance infection resolution and wound healing, reduce the requirement for systemic antibiotic therapy, and support antimicrobial stewardship initiatives in wound care.

Detecting bacterial infections in wounds: a review of biosensors and wearable sensors in comparison with conventional laboratory methods

Review on laboratory-based methods and biosensors and wearable sensors for detecting wound infection by aerobic and anaerobic bacteria.

Detection of bacterial fluorescence from in vivo wound biofilms using a point-of-care fluorescence imaging device

Wound biofilms must be identified to target disruption and bacterial eradication but are challenging to detect with standard clinical assessment. This study tested whether bacterial fluorescence imaging could detect porphyrin-producing bacteria within a biofilm using well-established in vivo models. Mouse wounds were inoculated on Day 0 with planktonic bacteria (n = 39, porphyrin-producing and non-porphyrin-producing species, 107  colony forming units (CFU)/wound) or with polymicrobial biofilms (n = 16, 3 biofilms per mouse, each with 1:1:1 parts Staphylococcus aureus/Escherichia coli/Enterobacter cloacae, 107  CFU/biofilm) that were grown in vitro. Mouse wounds inoculated with biofilm underwent fluorescence imaging up to Day 4 or 5. Wounds were then excised and sent for microbiological analysis. Bacteria-matrix interaction was assessed with scanning electron microscopy (SEM) and histopathology. A total of 48 hours after inoculation with planktonic bacteria or biofilm, red fluorescence was readily detected in wounds; red fluorescence intensified up to Day 4. Red fluorescence from biofilms persisted in excised wound tissue post-wash. SEM and histopathology confirmed bacteria-matrix interaction. This pre-clinical study is the first to demonstrate the fluorescence detection of bacterial biofilm in vivo using a point-of-care wound imaging device. These findings have implications for clinicians targeting biofilm and may facilitate improved visualisation and removal of biofilms.

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.

Real-time bacterial fluorescence imaging accurately identifies wounds with moderate-to-heavy bacterial burden

OBJECTIVE

Clinical evaluation of signs and symptoms (CSS) of infection is imperative to the diagnostic process. However, patients with heavily colonised and infected wounds are often asymptomatic, leading to poor diagnostic accuracy. Point-of-care fluorescence imaging rapidly provides information on the presence and location of bacteria. This clinical trial (#NCT03540004) aimed to evaluate diagnostic accuracy when bacterial fluorescence imaging was used in combination with CSS for identifying wounds with moderate-to-heavy bacterial loads.

METHODS

Wounds were assessed by study clinicians using NERDS and STONEES CSS criteria to determine the presence or absence of moderate-to-heavy bacterial loads, after which the clinician prescribed and reported a detailed treatment plan. Only then were fluorescence images of the wound acquired, bacterial fluorescence determined to be present or absent and treatment plan adjusted if necessary.

RESULTS

We examined 17 VLUs/2 DFUs. Compared with CSS alone, use of bacterial fluorescence imaging in combination with CSS significantly improved sensitivity (22% versus 72%) and accuracy (26% versus 74%) for identifying wounds with moderate-to-heavy bacterial loads (≥10⁴ CFU/g, p=0.002). Clinicians reported added value of fluorescence images in >90% of study wounds, including identification of wounds incorrectly diagnosed by CSS (47% of study wounds) and treatment plan modifications guided by fluorescence (73% of study wounds). Modifications included image-guided cleaning, treatment selection, debridement and antimicrobial stewardship.

CONCLUSION

Findings from this pilot study suggest that when used in combination with CSS, bacterial fluorescence may: (1) improve the diagnostic accuracy of identifying patients with wounds containing moderate-to-heavy bacterial loads and (2) guide more timely and appropriate treatment decisions at the point-of-care.

Amplicon sequencing provides more accurate microbiome information in healthy children compared to culturing

Next-Generation Sequencing (NGS) of 16S rRNA gene is now one of the most widely used application to investigate the microbiota at any given body site in research. Since NGS is more sensitive than traditional culture methods (TCMs), many studies have argued for them to replace TCMs. However, are we really ready for this transition? Here we compare the diagnostic efficiency of the two methods using a large number of samples (n = 1,748 fecal and n = 1,790 hypopharyngeal), among healthy children at different time points. Here we show that bacteria identified by NGS represented 75.70% of the unique bacterial species cultured in each sample, while TCM only identified 23.86% of the bacterial species found by amplicon sequencing. We discuss the pros and cons of both methods and provide perspective on how NGS can be implemented effectively in clinical settings.

Point-of-care fluorescence imaging predicts the presence of pathogenic bacteria in wounds: a clinical study

OBJECTIVE

Bacteria in chronic wounds are invisible to the naked eye and can lead to delayed wound healing. Point-of-care bacterial fluorescence imaging illuminates a wound with 405nm light, triggering bacteria to produce red fluorescence and enabling real-time bacterial localisation. Prospective, single-blind clinical trials (clinicaltrials.gov #NCT02682069, #NCT03091361) were conducted to determine the positive predictive value (PPV) of this red fluorescence for detecting bacteria in chronic wounds.

METHOD

Lower limb chronic wounds were imaged for bacterial fluorescence using the MolecuLight i:X imaging device. Regions positive for red fluorescence were discretely sampled using either biopsy or curettage to correlate red fluorescence signals to bacterial presence and analysed via gold standard quantitative polymerase chain reaction (qPCR) or via semi-quantitative culture analysis respectively.

RESULTS

A total of 60 lower limb chronic wounds were imaged. Quantitative PCR analysis of wound tissue biopsies obtained from regions of red fluorescence yielded a PPV of 100%. Total bacterial load in these areas was ≥10⁴ CFU/g. Semi-quantitative culture analysis of curettage scrapings from regions of red fluorescence yielded a PPV of 100%, with predominately moderate or heavy bacterial growth. There were nine distinct bacterial species detected, all common pathogens in chronic wounds. Staphylococcus aureus was the most prevalent species.

CONCLUSION

Bacterial fluorescence image-guided curettage or biopsy sampling positively predicts bacterial presence in wounds at potentially harmful levels, entirely eliminating the risk of false negative sampling. Fluorescence imaging of wounds offers clinicians real-time information on a wound's bacterial burden, insight which can influence treatment decisions at the point-of care.

The Frog Skin-Derived Antimicrobial Peptide Esculentin-1a(1-21)NH2 Promotes the Migration of Human HaCaT Keratinocytes in an EGF Receptor-Dependent Manner: A Novel Promoter of Human Skin Wound Healing?

One of the many functions of skin is to protect the organism against a wide range of pathogens. Antimicrobial peptides (AMPs) produced by the skin epithelium provide an effective chemical shield against microbial pathogens. However, whereas antibacterial/antifungal activities of AMPs have been extensively characterized, much less is known regarding their wound healing-modulatory properties. By using an in vitro re-epithelialisation assay employing special cell-culture inserts, we detected that a derivative of the frog-skin AMP esculentin-1a, named esculentin-1a(1-21)NH₂, significantly stimulates migration of immortalized human keratinocytes (HaCaT cells) over a wide range of peptide concentrations (0.025–4 μM), and this notably more efficiently than human cathelicidin (LL-37). This activity is preserved in primary human epidermal keratinocytes. By using appropriate inhibitors and an enzyme-linked immunosorbent assay we found that the peptide-induced cell migration involves activation of the epidermal growth factor receptor and STAT3 protein. These results suggest that esculentin-1a(1-21)NH₂ now deserves to be tested in standard wound healing assays as a novel candidate promoter of skin re-epithelialisation. The established ability of esculentin-1a(1-21)NH₂ to kill microbes without harming mammalian cells, namely its high anti-Pseudomonal activity, makes this AMP a particularly attractive candidate wound healing promoter, especially in the management of chronic, often Pseudomonas-infected, skin ulcers.

Fabrication of stimulus-responsive diatom biosilica microcapsules for antibiotic drug delivery

In this report, we employed surface-initiated atom transfer radical polymerisation to graft thermo-responsive copolymers of oligo(ethylene glycol) methacrylates from the surface of diatom biosilica microcapsules. We demonstrate the application of the resulting composites for thermo-responsive drug delivery.

Chronic wound repair and healing in older adults: current status and future research

Older adults are more likely to have chronic wounds than younger people, and the effect of chronic wounds on quality of life is particularly profound in this population. Wound healing slows with age, but the basic biology underlying chronic wounds and the influence of age-associated changes on wound healing are poorly understood. Most studies have used in vitro approaches and various animal models, but observed changes translate poorly to human healing conditions. The effect of age and accompanying multimorbidity on the effectiveness of existing and emerging treatment approaches for chronic wounds is also unknown, and older adults tend to be excluded from randomized clinical trials. Poorly defined outcomes and variables; lack of standardization in data collection; and variations in the definition, measurement, and treatment of wounds also hamper clinical studies. The Association of Specialty Professors, in conjunction with the National Institute on Aging and the Wound Healing Society, held a workshop, summarized in this article, to explore the current state of knowledge and research challenges, engage investigators across disciplines, and identify research questions to guide future study of age-associated changes in chronic wound healing.

Chronic wound repair and healing in older adults: current status and future research

The incidence of chronic wounds is increased among older adults, and the impact of chronic wounds on quality of life is particularly profound in this population. It is well established that wound healing slows with age. However, the basic biology underlying chronic wounds and the influence of age-associated changes on wound healing are poorly understood. Most studies have used in vitro approaches and various animal models, but observed changes translate poorly to human healing conditions. The impact of age and accompanying multi-morbidity on the effectiveness of existing and emerging treatment approaches for chronic wounds is also unknown, and older adults tend to be excluded from randomized clinical trials. Poorly defined outcomes and variables, lack of standardization in data collection, and variations in the definition, measurement, and treatment of wounds also hamper clinical studies. The Association of Specialty Professors, in conjunction with the National Institute on Aging and the Wound Healing Society, held a workshop, summarized in this paper, to explore the current state of knowledge and research challenges, engage investigators across disciplines, and identify key research questions to guide future study of age-associated changes in chronic wound healing.

First evidence of sternal wound biofilm following cardiac surgery

Management of deep sternal wound infection (SWI), a serious complication after cardiac surgery with high morbidity and mortality incidence, requires invasive procedures such as, debridement with primary closure or myocutaneous flap reconstruction along with use of broad spectrum antibiotics. The purpose of this clinical series is to investigate the presence of biofilm in patients with deep SWI. A biofilm is a complex microbial community in which bacteria attach to a biological or non-biological surface and are embedded in a self-produced extracellular polymeric substance. Biofilm related infections represent a major clinical challenge due to their resistance to both host immune defenses and standard antimicrobial therapies. Candidates for this clinical series were patients scheduled for a debridement procedure of an infected sternal wound after a cardiac surgery. Six patients with SWI were recruited in the study. All cases had marked dehiscence of all layers of the wound down to the sternum with no signs of healing after receiving broad spectrum antibiotics post-surgery. After consenting patients, tissue and/or extracted stainless steel wires were collected during the debridement procedure. Debrided tissues examined by Gram stain showed large aggregations of Gram positive cocci. Immuno-fluorescent staining of the debrided tissues using a specific antibody against staphylococci demonstrated the presence of thick clumps of staphylococci colonizing the wound bed. Evaluation of tissue samples with scanning electron microscope (SEM) imaging showed three-dimensional aggregates of these cocci attached to the wound surface. More interestingly, SEM imaging of the extracted wires showed attachment of cocci aggregations to the wire metal surface. These observations along with the clinical presentation of the patients provide the first evidence that supports the presence of biofilm in such cases. Clinical introduction of the biofilm infection concept in deep SWI may advance the current management strategies from standard antimicrobial therapy to anti-biofilm strategy.

Method to quantify live and dead cells in multi-species oral biofilm by real-time PCR with propidium monoazide

Real-time PCR (qPCR) is a widely used technique in analysing environmental and clinical microbiological samples. However, its main limitation was its inability to discriminate between live and dead cells.

Recently, propidium monoazide (PMA) together with qPCR has been used to overcome this problem, with good results for different bacterial species in different types of samples.

Our objective was to implement this technique for analysing mortality in multi-species oral biofilms formed in vitro with five oral bacteria: Streptococcus oralis, Streptococcus gordonii, Veillonella parvula, Fusobacterium nucleatum and Prevotella intermedia. We also tested its effectiveness on biofilms treated with an antiseptic solution containing 0.07% w/w cetylpyridinium chloride (CPC).

Standardisation of the qPCR-PMA method was performed on pure, heat-killed planktonic cultures of each species, detecting mortality higher than 4 log in S. oralis, S. gordonii and F. nucleatum and higher than 2 for V. parvula and P. intermedia. We obtained similar results for all species when using CPC.

When we analysed biofilms with qPCR-PMA, we found that the mortality in the non-CPC treated multi-species biofilms was lower than 1 log for all species. After treatment with CPC, the viability reduction was higher than 4 log in S. oralis and S. gordonii, higher than 3 log in F. nucleatum and P. intermedia and approximately 2 in V. parvula.

In short, we standardised the conditions for using qPCR-PMA in 5 oral bacterial species and proved its usefulness for quantification of live and dead cells in multi-species oral biofilms formed in vitro, after use of an antiseptic.

Wound care: biofilm and its impact on the latest treatment modalities for ulcerations of the diabetic foot

Biofilm is an increasingly important topic of discussion in the care of the chronic diabetic foot wound. Treatment modalities have focused on biofilm reduction or eradication through debridement techniques, topical therapies, negative pressure therapy, and ultrasound. In addition, advanced wound healing modalities, such as bioengineered alternative tissues, require optimal wound bed preparation with specific consideration of biofilm reduction before their application. Although fundamental principles of diabetic wound care still apply, critical thought must be given to biofilm before implementing a treatment plan for the closure of these complex wounds.

Clinically Addressing Biofilm in Chronic Wounds

BACKGROUND

A chronic wound is a wound that is arrested in the inflammatory phase of wound healing and cannot progress further. Over 90% of chronic wounds contain bacteria and fungi living within a biofilm construct.

THE PROBLEM

Each aggregation of microbes creates a distinct biofilm with differing characteristics so that a clinical approach has to be tailored to the specifics of a given biofilm. Defining the characteristics of that biofilm and then designing a therapeutic option particular to that biofilm is currently being defined.

BASIC/CLINICAL SCIENCE ADVANCES

Biofilm becomes resistant to therapeutic maneuvers at 48-96 h after formation. By repeatedly attacking it on a regular schedule, one forces biofilm to reattach and reform during which time it is susceptible to antibiotics and host defenses. Identifying the multiple bacteria and fungi that make up a specific biofilm using polymerase chain reaction (PCR) allows directed therapeutic maneuvers such as application of specific topical antibiotics and biocides to increase the effectiveness of the debridement.

CLINICAL CARE RELEVANCE

Most chronic wounds contain biofilm that perpetuate the inflammatory phase of wound healing. Combining debridement with using PCR to identify the bacteria and fungi within the biofilm allows for more targeted therapeutic maneuvers to eliminate a given biofilm.

CONCLUSION

Therapeutic options in addition to debridement are currently being evaluated to address biofilm. Using PCR to direct adjunctive therapeutic maneuvers may increase the effectiveness of addressing biofilm in a chronic wound.

Wound Healing Finally Enters the Age of Molecular Diagnostic Medicine

BACKGROUND

Many wounds are difficult to heal because of the large, complex community of microbes present within the wound.

THE PROBLEM

Classical laboratory culture methods do not provide an accurate picture of the microbial interactions or representation of microorganisms within a wound. There is an inherent bias in diagnosis based upon classical culture stemming from the ability of certain organisms to thrive in culture while others are underrepresented or fail to be identified in culture altogether. Chronic wounds also contain polymicrobial infections existing as a cooperative community that is resistant to antibiotic therapy.

BASIC/CLINICAL SCIENCE ADVANCES

New methods in molecular diagnostic medicine allow the identification of nearly all organisms present in a wound irrespective of the ability of these organisms to be grown in culture. Advances in DNA analyses allow absolute identification of microorganisms from very small clinical specimens. These new methods also provide a quantitative representation of all microorganisms contributing to these polymicrobial infections.

CLINICAL CARE RELEVANCE

Technological advances in laboratory diagnostics can significantly shorten the time required to heal chronic wounds. Identification of the genetic signatures of organisms present within a wound allows clinicians to identify and treat the primary organisms responsible for nonhealing wounds.

CONCLUSION

Advanced genetic technologies targeting the specific needs of wound care patients are now accessible to all wound care clinicians.

Microbiology of the skin and the role of biofilms in infection

The integrity of human skin is central to the prevention of infection. Acute and chronic wounds can develop when the integrity of skin as a barrier to infection is disrupted. As a multi-functional organ, skin possesses important biochemical and physical properties that influence its microbiology. These properties include a slightly acidic pH, a low moisture content, a high lipid content (which results in increased hydrophobicity) and the presence of antimicrobial peptides. Such factors have a role to play in preventing exogenous microbial colonisation and subsequent infection. In addition, the properties of skin both select for and enhance colonisation and biofilm formation by certain 'beneficial' micro-organisms. These beneficial micro-organisms can provide further protection against colonisation by potential pathogens, a process known as colonisation resistance. The aim of this paper is to summarise the microflora of skin and wounds, highlighting the role of certain micro-organisms and biofilms in associated infections.

Panbacterial real-time PCR to evaluate bacterial burden in chronic wounds treated with Cutimed™ Sorbact™

The impact of polymicrobial bacterial infection on chronic wounds has been studied extensively, but standard bacteriological analysis is not always sensitive enough. Molecular approaches represent a promising alternative to the standard bacteriological analysis. This work aimed to assess the usefulness of a panbacterial quantitative real-time PCR reaction to quantitate the total bacterial load in chronic wounds treated with Cutimed™ Sorbact™, a novel therapeutic approach based on hydrophobic binding of bacteria to a membrane. The results obtained by panbacterial real-time PCR on conserved sequences of the bacterial 16S gene show that the bacterial burden significantly decreased in 10 out of 15 healing chronic wounds, and did not change in 5 out of 5 non-healing chronic wounds. On the contrary, classical culture for S. aureus and P. aeruginosa, and real-time PCR for Bacteroides and Fusobacterium did not show any correlation with the clinical outcome. Our study also shows that quantification of chronic wounds by panbacterial real-time PCR is to be performed on biopsies and not on swabs. These results show that panbacterial real-time PCR is a promising and quick method of determining the total bacterial load in chronic wounds, and suggest that it might be an important biomarker for the prognosis of chronic wounds under treatment.

Molecular diagnostics and personalised medicine in wound care: assessment of outcomes

OBJECTIVE

This large, level A, retrospective cohort study set out to compare healing outcomes in three large cohorts of wound patients managed universally for bioburden: standard of care group, who were prescribed systemic antibiotics on the basis of empiric and traditional culture-based methodologies; treatment group 1, who were prescribed an improved selection of systemic antibiotics based on the results of molecular diagnostics; treatment group 2 who received personalised topical therapeutics (including antibiotics) based on the results of molecular diagnostics.

METHOD

Apart from the differences in diagnostic methods and antibiotic treatments described above, all three cohorts were subjected to the same biofilm-based wound care protocol, which included evaluation of the host and bioburden, frequent sharp debridement, use of wound dressings and comprehensive standard care (reperfusion therapy, nutritional support, offloading, compression and management of comorbidities).

RESULTS

In all, 1378 patients were recruited into the study. In the standard of care group 48.5% of patients (244/503) healed completely during the 7-month study period. This increased to 62.4% (298/479) in treatment group 1 and 90.4% (358/396) in treatment group 2. Cox proportional hazards analysis revealed the time to complete closure decreased by 26% in treatment group 1 (p<0.001) and 45.9% in treatment group 2 (p<0.001) compared with the standard of care group. Patients in treatment group 2 had >200% better odds of healing at any given time point compared with the other cohorts.

CONCLUSION

Implementation of personalised topical therapeutics guided by molecular diagnosis resulted in statistically and clinically significant improvements in outcome. The integration of molecular diagnostics and personalised medicine provides a directed and targeted approach to wound care.

CONFLICT OF INTEREST

SED and RDW are owners of PathoGenius Laboratories, a clinical diagnostic laboratory. SED and RDW are owners of Research and Testing Laboratory, which develops molecular diagnostics. CJ and JK are clinical advisors for PathoGenius. CJ and JK are owners of Southeastern Medical Compounding, Savannah, GA and Southeastern Medical Technologies, Savannah, GA.

The role of biofilms: are we hitting the right target?

BACKGROUND

Chronic infections affect 17 million people yearly, and approximately 550,000 people die each year from, or with, their chronic infections. Acute and chornic infection differences are well known to clinicians, but the role of bacteria in producing these clinical differences remains poorly understood.

METHODS

This review relies on basic science, clinical studies, and a general review of the medical biofilm literature. The basic science studies are level A and B quality of evidence. The clinical studies are mainly retrospective cohort (level B) and case studies (level C). The biofilm literature includes reviews with varying levels of evidence. All articles have been peer reviewed and meet the standard of evidence-based medicine.

RESULTS

Acute infections are associated with planktonic bacteria and must be diagnosed rapidly and accurately to prevent tissue damage and/or death. In contrast, biofilm behavior pursues a more parasitic course by producing sustained host hyperinflammation, with the biofilm feeding on plasma exudate. Chronic infections vacillate over long periods of time, responding only partially to antibiotics and reemerging once the antibiotics are withdrawn. Chronic wounds exhibit similar clinical behavior seen in other chronic infections and are associated with biofilm phenotype bacteria on their surface. Biofilm infections, such as chronic wounds, cannot be adequately diagnosed with current clinical cultures; therefore, molecular methods are necessary.

CONCLUSIONS

Biofilm phenotype bacteria require multiple concurrent strategies, including débridement and targeted antibiofilm agents. Biofilm phenotype bacteria predominate on the surface of wounds, and biofilm-based management improves wound healing outcomes, indicating that biofilm is the right target for managing the bioburden barrier of chronic wounds.

Diagnosis and management of chronic infection

High-energy penetrating extremity injuries are often associated with severe open fractures that have varying degrees of soft-tissue contamination and tenuous soft-tissue coverage. The result is a relatively high prevalence of chronic osteomyelitis compared with that in civilian trauma patients. Diagnosing chronic osteomyelitis requires a careful history and thorough physical and radiographic examinations. Cross-sectional imaging can help delineate the extent of bony involvement, and scintigraphy can be used as a diagnostic tool and to gauge response to treatment. Clinical staging also directs surgical management. Adequacy of débridement remains the most important clinical predictor of success; thus, adopting an oncologic approach to complete (ie, wide) excision is important. Reconstruction can be safely performed by a variety of methods; however, proper staging and patient selection remain critical to a successful outcome. Although systemic and depot delivery of antibiotics plays a supporting role in the treatment of chronic osteomyelitis, the ideal dosing regimens, and the duration of treatment, remain controversial.

Current concepts regarding the effect of wound microbial ecology and biofilms on wound healing

Biofilms are a collection of microbes that adhere to surfaces by manufacturing a matrix that shields them from environmental elements. Wound biofilms are difficult to evaluate clinically, and standard culture methods are inadequate for capturing the true bioburden present in the biofilm. New molecular techniques provide the means for rapid detection and evaluation of wound biofilms, and may prove to be useful in the clinical setting. Studies have shown that many commercial topical agents and wound dressings in use are ineffective against the biofilm matrix. At this stage, mechanical debridement appears to be essential in the eradication of a wound biofilm. Topical antimicrobial agents and antibiotics may be effective in the treatment of the wound bed after debridement in the prevention of biofilm reformation.

Molecular diagnosis of Raoultella planticola infection of a surgical site

Raoultella planticola has been rarely diagnosed in clinical specimens. A case of a polymicrobial surgical site infection primarily caused by R. planticola in a 66-year-old Caucasian male with a fractured left tibia after an open reduction internal fixation of his left ankle is described and confirms this organism to be an opportunistic human pathogen. This pathogen was diagnosed with rapid clinical molecular pathogen diagnostic methods, which allowed an appropriate therapy to be implemented, thereby improving prognosis.

A prospective randomised open label study to evaluate the potential of a new silver alginate/carboxymethylcellulose antimicrobial wound dressing to promote wound healing

The aim of this study was to observe both the clinical signs and symptoms of wounds at risk of infection, that is critically colonised (biofilm infected) and antimicrobial-performance of an ionic silver alginate/carboxymethylcellulose (SACMC) dressing, in comparison with a non silver calcium alginate fibre (AF) dressing, on chronic venous leg and pressure ulcers. Thirty-six patients with venous or pressure ulcers, considered clinically to be critically colonised (biofilm infected), were randomly chosen to receive either an SACMC dressing or a non silver calcium AF dressing. The efficacy of each wound dressing was evaluated over a 4-week period. The primary study endpoints were prevention of infection and progression to wound healing. The SACMC group showed a statistically significant (P = 0.017) improvement to healing as indicated by a reduction in the surface area of the wound, over the 4-week study period, compared with AF controls. In conclusion, the SACMC dressing showed a greater ability to prevent wounds progressing to infection when compared with the AF control dressing. In addition, the results of this study also showed an improvement in wound healing for SACMC when compared with a non silver dressing.

Biofilms in chronic infections - a matter of opportunity - monospecies biofilms in multispecies infections

It has become evident that aggregation or biofilm formation is an important survival mechanism for bacteria in almost any environment. In this review, we summarize recent visualizations of bacterial aggregates in several chronic infections (chronic otitis media, cystic fibrosis, infection due to permanent tissue fillers and chronic wounds) both as to distribution (such as where in the wound bed) and organization (monospecies or multispecies microcolonies). We correlate these biofilm observations to observations of commensal biofilms (dental and intestine) and biofilms in natural ecosystems (soil). The observations of the chronic biofilm infections point toward a trend of low bacterial diversity and sovereign monospecies biofilm aggregates even though the infection in which they reside are multispecies. In contrast to this, commensal and natural biofilm aggregates contain multiple species that are believed to coexist, interact and form biofilms with high bacterial and niche diversity. We discuss these differences from both the diagnostic and the scientific point of view.

Biofilms and bacterial imbalances in chronic wounds: anti-Koch

Microbial imbalances and synergistic relationships between bacteria in medically important biofilms are poorly researched. Consequently, little is known about how synergy between bacteria may increase the net pathogenic effect of a biofilm in many diseases and infections, including chronic wounds. Microbial synergy in chronic wounds may increase virulence and pathogenicity, leading to enhanced tissue degradation, malodour and in some cases, an impairment of the host immune response. Microbial synergy and growth within a biofilm provide a competitive advantage to the microorganisms cohabiting in a wound, thereby promoting their survival and tolerance and resistance to antimicrobial agents. The aim of this article was to provide greater insight into microbial imbalances found within wound biofilms and the significance they may have on non healing and infected wounds. We also present two possible hypotheses which could explain the role microorganisms play in non healing chronic wounds and offer possible strategies for combating harmful and detrimental biofilms.

A comparison of bacterial composition in diabetic ulcers and contralateral intact skin

An extensive portion of the healthcare budget is allocated to chronic human infection. Chronic wounds in particular are a major contributor to this financial burden. Little is known about the types of bacteria which may contribute to the chronicity, biofilm and overall bioburden of the wound itself. In this study we compare the bacteriology of wounds and associated intact skin. Wound and paired intact skin swabs (from a contralateral location) were collected. The bacterial diversity was determined using bacterial Tag-encoded FLX amplicon pyrosequencing (bTEFAP). Diversity analysis showed intact skin to be significantly more diverse than wounds on both the species and genus levels (3% and 5% divergence). Furthermore, wounds show heightened levels of anaerobic bacteria, like Peptoniphilus, Finegoldia, and Anaerococcus, and other detrimental genera such as Corynebacterium and Staphylococcus. Although some of these and other bacterial genera were found to be common between intact skin and wounds, notable opportunistic wound pathogens were found at lower levels in intact skin. Principal Component Analysis demonstrated a clear separability of the two groups. The findings of the study not only greatly support the hypothesis of differing bacterial composition of intact skin and wounds, but also contribute additional insight into the ecology of skin and wound microflora. The increased diversity and lowered levels of opportunistic pathogens found in skin make the system highly distinguishable from wounds.

Propagation of anaerobic bacteria within an aerobic multi-species chronic wound biofilm model

OBJECTIVE

Most chronic wound biofilms have been shown to have significant populations of anaerobes. In order to better screen antimicrobial and antibiofilm therapeutics, we evaluated the ability of key anaerobes to incorporate and propagate within our aerobic chronic wound biofilm.

METHOD

We had previously developed a rapid model to simulate polymicrobial chronic wound biofilms. This model incorporated meticillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE) and Pseudomonas aeruginosa. The model was used along with a variety of anaerobes to determine whether this biofilm model would support propagation of anaerobes similar to that we have identified in chronic wounds.

RESULTS

Using our previously defined Lubbock Chronic Wound Biofilm (LCWB) model combined with quantitative PCR, anaerobic bacteria were shown to proliferate through integration into the biofilm under aerobic conditions. Using electron microscopy we show close association between aerobes and anaerobes within the biofilm suggesting a synergistic relationship.

CONCLUSION

We have expanded the utility of the LCBW to show the ability of clinically significant anaerobic bacteria to thrive in aerobic conditions. The expansion of this model can further simulate the functional characteristics of chronic wound pathogenic biofilms and the species that dwell within them allowing improved ability to evaluate therapeutics that target anaerobes.

Bacterial diversity in surgical site infections: not just aerobic cocci any more

OBJECTIVE

To evaluate the microbial diversity in chronic surgical site infections (SSIs).

METHOD

Bacterial populations in 23 chronic SSIs were identified using bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP),which is an universal bacterial identification method.These results were then validated using quantitative polymerase chain reaction (qPCR).

RESULTS

bTEFAP identified two previously uncharacterised Bacteroidales in all of the SSIs and showed that it was the predominant population in the majority of these chronic wounds. Other bacteria identified included Corynebacterium spp., Peptoniphilus spp., Staphylococcus spp., Staphylococcus aureus, Serratia marcescens, Prevotella spp. and Pseudomonas aeruginosa. Rarefaction analysis of the data indicated that, on average, six genera occurred in any given SSI, suggesting that such infections are multispecies. On average, over 60% of the bacteria evaluated in the SSIs were anaerobic bacilli. The previous literature indicates that aerobic cocci predominate in such wounds.

CONCLUSION

This modern molecular survey indicates that our previous understanding of which bacteria cause SSIs may be faulty. The high prevalence of anaerobic bacilli and the overwhelming predominance of two previously uncharacterised Bacteroidales suggest that such bacteria may be a leading contributor to such infections. Further research on the identification and treatment of such bacteria are warranted.

Evaluation of the bacterial diversity among and within individual venous leg ulcers using bacterial tag-encoded FLX and titanium amplicon pyrosequencing and metagenomic approaches

Background

Approximately 1 out of every 100 individuals has some form of venous insufficiency, which can lead to chronic venous disease and Venous Leg Ulcer (VLU). There are known underlying pathologies which contribute to the chronic nature of VLU including biofilm phenotype infections.

Results

Using pyrosequencing based approaches we evaluated VLU to characterize their microbial ecology. Results show that VLU infections are polymicrobial with no single bacterium colonizing the wounds. The most ubiquitous and predominant organisms include a previously uncharacterized bacteroidales, various anaerobes, Staphylococcus, Corynebacterium, and Serratia. Topological analysis of VLU show some notable differences in bacterial populations across the surface of the wounds highlighting the importance of sampling techniques during diagnostics. Metagenomics provide a preliminary indication that there may be protozoa, fungi and possibly an undescribed virus associated with these wounds.

Conclusion

The polymicrobial nature of VLU and previous research on diabetic foot ulcers and surgical site infections suggest that the future of therapy for such wounds lies in the core of the logical and proven multiple concurrent strategy approach, which has been termed "biofilm-based wound care" and the use of individualized therapeutics rather than in a single treatment modality.

Identification of yeast in chronic wounds using new pathogen-detection technologies

OBJECTIVE

To evaluate the ability of two new diagnostic methods to detect and accurately identify yeast associated with chronic wound infections.

METHOD

Fungal tag-encoded FLX amplicon pyrosequencing (fTEFAP), a universal fungal identification method, bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP), a universal bacterial identification method, and a new quantitative polymerase chain reaction (qPCR) wound pathogen panel were used to evaluate three chronic wounds suspected to contain yeast.

RESULTS

Forty wound samples were analysed in addition to the three samples suspected of containing yeast. The qPCR panel, which targets Candida albicans, detected this yeast in two of the three wound samples. In contrast, fTEFAP detected yeast in each of the three samples: two showed Candida albicans and the third Candida parapsilosis. fTEFAP also identified a lower level of Candida tropicalis in one of the wounds that was positive for Candida albicans. The qPCR wound panel results were returned within two hours, while the fTEFAP results were returned within 24 hours.

CONCLUSION

Two new molecular methods have been developed to aid wound pathogen diagnostics. The quantitative PCR wound panel is rapid but is limited to major wound-associated bacteria and yeasts. The universal fTEFAP and bTEFAP methods take 24 hours to return results but are able to detect the relative contribution of any bacteria of yeast in a chronic wound diagnostic sample.

DECLARATION OF INTEREST

Southwest Regional Wound Care Center is a clinical wound-care provider seeking to improve the ability of wound care practitioners to help patients. The Research and Testing Laboratory develops molecular methods including fTEFAP, bTEFAP and the quantitative PCR wound panel.

Regular debridement is the main tool for maintaining a healthy wound bed in most chronic wounds

Sharp debridement is the most clinically and cost-effective way of physically removing and suppressing a biofilm. Continued debridement, as part of a multifaceted treatment strategy, will keep the biofilm in a weakened state.