A clinical algorithm for wound biofilm identification.

Recognition of the existence of biofilm in chronic wounds is increasing among wound care practitioners, and a growing body of evidence indicates that biofilm contributes significantly to wound recalcitrance. While clinical guidelines regarding the involvement of biofilm in human bacterial infections have been proposed, there remains uncertainty and lack of guidance towards biofilm presence in wounds. The intention of this report is to collate knowledge and evidence of the visual and indirect clinical indicators of wound biofilm, and propose an algorithm designed to facilitate clinical recognition of biofilm and subsequent wound management practices.

A clinical algorithm for wound biofilm identification.

Recognition of the existence of biofilm in chronic wounds is increasing among wound care practitioners, and a growing body of evidence indicates that biofilm contributes significantly to wound recalcitrance. While clinical guidelines regarding the involvement of biofilm in human bacterial infections have been proposed, there remains uncertainty and lack of guidance towards biofilm presence in wounds. The intention of this report is to collate knowledge and evidence of the visual and indirect clinical indicators of wound biofilm, and propose an algorithm designed to facilitate clinical recognition of biofilm and subsequent wound management practices.

Topical antimicrobial protection of postoperative surgical sites at risk of infection with Propionibacterium acnes: an in-vitro study.

BACKGROUND: Propionibacterium acnes is an increasingly recognized pathogen in surgical site infections, particularly in relation to joint replacements and spinal procedures. Due to its low virulence and slow-growing nature, clinical signs of infection may be prolonged, and diagnosis is often challenging. As a consequence, appropriate presurgical skin preparation and postsurgical protection of the wound using antimicrobial dressings are important considerations in the prevention of surgical site infections caused by P. acnes. AIM: To investigate the antimicrobial efficacy of a silver-containing gelling fibre wound dressing against P. acnes using stringent in-vitro models that simulated a variety of wound conditions. METHODS: A simulated wound fluid model was used to quantify the killing capacity of the silver-containing dressing over time under conditions that mimicked a heavily exuding wound. A simulated colonized shallow wound model was used to investigate the impact of dressing conformability on antimicrobial activity, and a third model was designed to measure the efficacy of the dressing on bacteria embedded within a simulated colonized wound surface. FINDINGS: The in-vitro data demonstrated that the silver-containing wound dressing was bactericidal against P. acnes, it maintained its killing effect over a prolonged period (seven days) under conditions simulating excessive exudate, and the gelled dressing matrix (following hydration) enabled the dressing to conform to a simulated wound topography, thus optimizing antimicrobial activity in a shallow wound model. CONCLUSION: Based on the in-vitro data generated, use of the silver-containing dressing as part of a postoperative care protocol may help to minimize the risk of prolonged and debilitating surgical site infections caused by P. acnes.

Potential implications of biofilm in chronic wounds: a case series.

Bacterial biofilm is increasingly suspected as being a significant barrier to wound healing. Bacteria predominantly attach to surfaces in their natural habitats and form biofilm; in this state they adapt to, and tolerate, the hostilities in their surrounding environment. The purpose of this clinical observational study was to consider chronic wound biofilm in relation to other factors that are implicated in wound recalcitrance, such as peripheral arterial disease, wound infection, osteomyelitis and moisture imbalance. Based on our clinical observations, it is possible that links exist between wound biofilm and other underlying pathophysiological factors, and that biofilm may also provide clues to the involvement of such factors. Recognising and managing these factors collectively may be important in addressing recalcitrance and facilitating wound progression.

Bacterial resistance to silver in wound care.

Ionic silver exhibits antimicrobial activity against a broad range of micro-organisms. As a consequence, silver is included in many commercially available healthcare products. The use of silver is increasing rapidly in the field of wound care, and a wide variety of silver-containing dressings are now commonplace (e.g. Hydrofiber dressing, polyurethane foams and gauzes). However, concerns associated with the overuse of silver and the consequent emergence of bacterial resistance are being raised. The current understanding of the biochemical and molecular basis behind silver resistance has been documented since 1998. Despite the sporadic evidence of bacterial resistance to silver, there have been very few studies undertaken and documented to ascertain its prevalence. The risks of antibacterial resistance developing from the use of biocides may well have been overstated. It is proposed that hygiene should be emphasized and targeted towards those applications that have demonstrable benefits in wound care. It is the purpose of this review to assess the likelihood of widespread resistance to silver and the potential for silver to induce cross-resistance to antibiotics, in light of its increasing usage within the healthcare setting.

Microbicidal properties of a silver-containing hydrofiber dressing against a variety of burn wound pathogens.

Partial-thickness burns are often characterized by microbial contamination and copious exudate produced during the early postburn period. Consequently, topical wound management often relies on the use of antimicrobial agents and absorbent dressings, and an AQUACEL Hydrofiber Dressing containing ionic silver has been designed to meet such needs. To assess the antimicrobial properties of the AQUACEL Hydrofiber dressing, samples were challenged with a wide variety of recognized burn wound pathogens in a simulated wound fluid model. Dressing samples were inoculated with the challenge organisms at time zero and then reinoculated on days 4 and 9 to mimic the worst-case clinical scenario. The dressing was shown to be microbicidal against aerobic and anaerobic bacteria (including antibiotic-resistant strains), yeasts, and filamentous fungi during a 14-day test period. Based on our results, the silver-containing dressing is likely to provide a barrier to infection, in addition to providing proven fluid-handling benefits of the AQUACEL Hydrofiber dressing, in the management of partial-thickness burns.

Scanning electron microscopic examination of bacterial immobilisation in a carboxymethyl cellulose (AQUACEL) and alginate dressings.

Dressings have been applied to open wounds for centuries. Traditionally they have been absorbent, permeable materials, i.e. gauze that could adhere to desiccated wound surfaces, inducing trauma on removal. With the advent of modern wound care products many dressings are now capable of absorbing large volumes of exudate whilst still continuing to provide a moist wound healing environment. Equally important is their ability to lock exudate in the dressing (i.e. bacterial retention within the dressing matrix) such that upon removal from a wound surface bacterial dispersion is minimised. In these studies detailed scanning electron microscopy techniques have demonstrated the fluid controlling properties of alginate wound dressings and a carboxymethylated cellulose wound dressing (AQUACEL) Hydrofiber) dressing (CMCH)). It was demonstrated that following hydration of the latter wound dressing, the subsequent formation of a cohesive gel was effective in encapsulating large populations of potentially pathogenic bacteria such as Psuedomonas aeruginosa and Staphylococcus aureus under the gelled surface, as well as being immobilised within the swollen fibres. In contrast, hydrated alginate wound dressings did not form a uniform, cohesive gel structure, with the result that fewer bacteria were immobilised within the gel matrix. Many bacteria were trapped on individual, non-hydrated fibres. The unique absorbent gelling properties of the CMCH dressing appears to provide an ideal environment for immobilising bacteria.

Wound microbiology and associated approaches to wound management.

The majority of dermal wounds are colonized with aerobic and anaerobic microorganisms that originate predominantly from mucosal surfaces such as those of the oral cavity and gut. The role and significance of microorganisms in wound healing has been debated for many years. While some experts consider the microbial density to be critical in predicting wound healing and infection, others consider the types of microorganisms to be of greater importance. However, these and other factors such as microbial synergy, the host immune response, and the quality of tissue must be considered collectively in assessing the probability of infection. Debate also exists regarding the value of wound sampling, the types of wounds that should be sampled, and the sampling technique required to generate the most meaningful data. In the laboratory, consideration must be given to the relevance of culturing polymicrobial specimens, the value in identifying one or more microorganisms, and the microorganisms that should be assayed for antibiotic susceptibility. Although appropriate systemic antibiotics are essential for the treatment of deteriorating, clinically infected wounds, debate exists regarding the relevance and use of antibiotics (systemic or topical) and antiseptics (topical) in the treatment of nonhealing wounds that have no clinical signs of infection. In providing a detailed analysis of wound microbiology, together with current opinion and controversies regarding wound assessment and treatment, this review has attempted to capture and address microbiological aspects that are critical to the successful management of microorganisms in wounds.

Microbial involvement in chronic wound malodour.

The role of specific micro-organisms in producing chronic wound malodour was investigated by directly comparing odour severity and microbiology in infected and non-infected leg ulcers. Malodour was most frequently associated with infected wounds involving mixed aerobic and anaerobic, Gram-positive and Gram-negative microbial populations. Infected ulcers that were not characterised by an offensive odour were rarely colonised with anaerobic bacteria. A reduced incidence of pigmented and non-pigmented Gram-negative anaerobes (Bacteriodes spp, Prevotella spp, Porphyromonas spp) was evident in non-infected, non-malodorous leg ulcers. These observations emphasise the significance of specific anaerobic bacteria in the generation of wound malodour, and it is probable that their effect is potentiated by coexistence with mixed facultative micro-organisms.

The microbiology of infected and noninfected leg ulcers.

BACKGROUND: A clinical study was undertaken to investigate and compare specifically the aerobic and anaerobic microbiology of infected and noninfected leg ulcers. METHODS: Leg ulcers, defined as being infected on the basis of clinical signs, were swab sampled and investigated for aerobic and anaerobic microorganisms using stringent isolation and identification techniques. RESULTS: Two hundred and twenty isolates were cultured from 44 infected leg ulcers, in comparison with 110 isolates from 30 noninfected leg ulcers. Statistical analysis indicated a significantly greater mean number of anaerobic bacteria per infected ulcer (particularly Peptostreptococcus spp. and Prevotella spp.) in comparison with the noninfected ulcer group (2.5 vs. 1.3, respectively) (P < 0.05). Also, anaerobes represented 49% of the total microbial composition in infected leg ulcers compared with 36% in noninfected leg ulcers. The mean numbers of aerobes per wound in the two ulcer groups were not statistically different (P > 0.05). The study failed to demonstrate a clear correlation between commonly implicated facultative pathogens and wound infection. The isolation rate of Pseudomonas aeruginosa was generally low and, although Staphylococcus aureus was a frequent isolate in both wound types, it was more prevalent in noninfected leg ulcers. CONCLUSIONS: This study has demonstrated the complex aerobic-anaerobic microflora which exists in leg ulcers, the prevalence of anaerobes in infected wounds, and a poor correlation between the presence of specific aerobic pathogens and wound infection. In view of these findings, the role of microbial synergistic interactions in the pathogenesis of chronic wound infection may be of greater clinical importance than the isolated involvement of any specific potential pathogen.

Adsorption of serum-derived proteins by primary dressings: implications for dressing adhesion to wounds.

Using an in vitro immunolocalization technique, an exploratory study was carried out into the serum-derived protein adsorption capacity and the cell adherence of a traditional gauze dressing versus a new gelling fibre gauze dressing. We found that the traditional gauze dressing adsorbed protein more readily than the new dressing. The findings indicate that reduced binding of serum proteins to the surface of the gelling fibre dressing may help reduce the adherence characteristics for this type of dressing, minimising trauma and possibly reducing the acute pain experienced during dressing changes.

Infection control properties of some wound dressings.

The ability of some wound dressings to sequester and retain micro-organisms associated with wound fluid is perceived to provide beneficial properties regarding infection control. This study used an in vitro model to investigate and compare such properties in a range of fibrous absorbent dressings (alginate, hydrofibre and hydrophobic). Dressings were challenged with a simulated wound fluid containing common wound pathogens (Staphylococcus aureus or Pseudomonas aeruginosa). Bacterial sequestering and binding levels were monitored over time. A hydrofibre dressing and two calcium alginate dressings were shown to effectively sequester challenge organisms from a simulated wound fluid. However, the hydrophobic and hydrofibre dressings produced statistically significant results in their ability to adsorb and retain challenge organisms (p < 0.05). These investigations have demonstrated that a hydrofibre dressing effectively sequesters and retains micro-organisms upon exposure to simulated wound fluid, and may therefore provide a passive mechanism for reducing the microbial load in wounds and in the surrounding environment. Further in vivo studies are required to investigate these dressing properties.