The efficacy of topical agents used in wounds for managing chronic biofilm infections: A systematic review.

OBJECTIVES: Clinicians have increasingly adopted the widespread use of topical agents to manage chronic wound infections, despite limited data on their effectiveness in vivo. This study sought to evaluate the evidence for commonly employed topical agents used in wounds for the purpose of treating chronic infections caused by biofilm. METHOD: We included in vitro, animal and human in vivo studies where topical agents were tested for their efficacy against biofilms, for use in wound care. For human studies, we only included those which utilised appropriate identification techniques for visualising and confirming the presence of biofilms. RESULT: A total of 640 articles were identified, with 43 included after meeting eligibility. In vitro testing accounted for 90% (n = 39) of all included studies, five studies using animal models and three human in vivo studies. Sixteen different laboratory models were utilised, with the most frequent being the minimum biofilm eradication concentration (MBEC™) / well plate assay (38%, n = 15 of 39). A total of 44 commercially available topical agents were grouped into twelve categories with the most commonly tested agents being silver, iodine and polyhexamethylene biguanide (PHMB). In vitro results on efficacy demonstrated iodine as having the highest mean log10 reductions of all agents (4.81, ±3.14). CONCLUSION: There is large disparity in the translation of laboratory studies to researchers undertaking human trials relating to the effectiveness of commercially available topical agents. There is insufficient human in vivo evidence to definitively recommend any commercially available topical agent over another for the treatment of chronic wound biofilms. The heterogeneity identified between study designs (in vitro to in vivo) further limits the generalisability of results.

The Efficacy of Tetrasodium EDTA on Biofilms.

The aetiology of delayed wound healing characteristic of a chronic wound is relatively unknown but is thought to be due to a combination of the patient's underlying pathophysiology and external factors including infection and biofilm formation. The invasion of the wound by the hosts' resident microbiome and exogenous microorganisms can lead to biofilm formation. Biofilms have increased tolerance to antimicrobial interventions and constitute a concern to chronic wound healing. Consequently, anti-biofilm technologies with proven efficacy in areas outside of wound care need evaluation to determine whether their efficacy could be relevant to the control of biofilms in wounds. The aim of this study was to assess the anti-biofilm capabilities of tetrasodium EDTA (t-EDTA) as a stand-alone liquid and when incorporated in low concentrations into wound dressing prototypes. Results demonstrated that a low concentration of t-EDTA (4%) solution was able to kill Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), S. epidermidis, Pseudomonas aeruginosa and Enterococcus faecalis within in vitro biofilms after a 24-h contact time. The incorporation of low levels of t-EDTA into prototype fibrous wound dressings resulted in a 3-log reduction of bacteria demonstrating its microbicidal ability. Furthermore, hydrogels incorporating only a 0.2% concentration of t-EDTA (at preservative levels) caused a small reduction in biofilm. In conclusion, these studies show that t-EDTA as a stand-alone agent is an effective anti-biofilm agent in vitro. We have demonstrated that t-EDTA is compatible with numerous wound dressing platforms. EDTA could provide an essential tool to manage biofilm-related infections and should be considered as an anti-biofilm agent alone or in combination with other antimicrobials or technologies for increased antimicrobial performance in recalcitrant wounds.

Surfactants and their role in wound cleansing and biofilm management.

Surfactants are widely used as detergents, emulsifiers, wetting agents, foaming agents and dispersants in the cosmetics, hygiene, food and oil industries. Their use in a clinical setting is also common, particularly within the field of wound care. Many wound cleansers contain surfactants and subsequently there is available data that shows the growing potential of these wound cleansers in the enhancement of wound closure. The presence of microorganisms in wounds has been recognised as a significant factor that delay healing. In complex or chronic wounds that are complicated by biofilms, persistent inflammation or the production of non-viable tissue and slough, the use of surfactants has been shown to aid in the removal of these barriers to wound healing. The use of concentrated surfactant(poloxamer) based wound dressings represent an important component of wound management. Consequently, this article will discuss the effect of clinically used surfactants, with specific focus on a concentrated poloxamer for use against wound biofilm.

Importance of biofilm formation in surgical infection.

BACKGROUND: Biofilms are ubiquitous, and have been observed in both acute and chronic wounds. Their role in wound healing and infection, however, remains controversial. The aim of this review was to provide an overview of the role and relevance of biofilms to surgical wounds. METHODS: A search of PubMed, Science Direct and Web of Science databases was performed to identify studies related to biofilms. Specifically, studies were sought in acute and chronic wounds, and the management and treatment of non-healing and infected skin and wounds. RESULTS: Biofilms may develop in all open wounds. In chronic wounds, biofilms may play a role in prolonging and preventing healing, causing chronic inflammation and increasing the risk of infection. Controversies exist regarding the methods presently employed for biofilm detection and management and few data exist to underpin these decisions. CONCLUSION: Biofilms in acute surgical and chronic wounds appear to cause a delay in healing and potentially increase the risk of infection. Biofilms can be prevented and once developed can be controlled using wound desloughing and debridement.

Slough and biofilm: removal of barriers to wound healing by desloughing.

The presence of non-viable tissue in a chronic wound presents a barrier against effective wound healing, hence removal facilitates healing and reduces areas where microorganisms can attach and form biofilms, effectively reducing the risk of infection. Wound debridement is a necessary process in those wounds that have evidence of cellular debris and non-viable tissue. As slough is a form of non-viable tissue we hypothesise that it will support the attachment and development of biofilms. Biofilms are entities that have serious implications in raising the risk of infection and delaying wound healing. In those wounds that contain only slough, high-risk debridement methods are not considered necessary for its removal. The use of mechanical techniques for removing the slough is regarded as posing a much lower risk to the patient and the wound bed. The process of removing slough from a wound is referred to as 'desloughing'. We propose that mechanical desloughing is a low-risk method of debridement to aid the specific removal of slough. Slough in a wound is a recurrent issue for a large majority of patients. Consequently, desloughing should not be deemed a one-off process but an on-going procedure referred to as 'maintenance desloughing'. Maintenance desloughing will help to achieve and maintain a healthy wound bed and aid the removal of wound biofilms, facilitating wound healing.

In vitro antimicrobial efficacy of a silver alginate dressing on burn wound isolates.

OBJECTIVE: To test the antimicrobial effectiveness of a silver alginate dressing on opportunistic pathogens, namely meticillin-sensitive Staphylococcus aureus (MSSA) and meticillin-resistant Staphylococcus aureus (MRSA), Klebsiella spp., Enterococcus faecalis, Enterococcus faecium, Pseudomonas aeruginosa, Escherichia coli, Enterobacter sakazakii, Enterobacter cloacae, Serratia marcescens, Chryseobacterium indologenes, Proteus vulgaris and Acinetobacter baumannii. METHOD: In total, 40 microorganisms were isolated from patients attending three burn centres in the US and evaluated for their susceptibility to a silver alginate wound dressing, employing a corrected zone of inhibition assay, conducted on Mueller Hinton agar (MHA). RESULTS: The sizes of the corrected zones of inhibition varied between and within genera. For example, all Acinetobacter baumannii strains were found to be sensitive to ionic silver at pH 7, with a mean of 2.8mm, compared with 3.5mm at pH 5.5. The silver alginate dressing also demonstrated activity on all strains of Enterobacter and Escherichia coli, with susceptibility to the silver alginate dressing enhanced at pH 5.5. For Enterococcus spp. the average corrected zone of inhibition at pH 7 was 3.6mm, versus 4.9mm at pH 5.5. All strains of Pseudomonas aeruginosa were found to be sensitive to the silver alginate dressing. The average corrected zone of inhibition was 6.9mm at pH 7, compared with 8mm at pH 5.5. For MRSA and Staphylococcus aureus, it ranged from 4.5mm to 7.5mm at pH 7. When the pH was decreased to 5.5, the corrected zone of inhibition increased. CONCLUSION: This study demonstrates the activity of a silver alginate dressing on a wide range of burn isolates, including antibiotic-resistant bacteria, isolated from three different burn centres in the US. It also highlights the possible importance of pH and its potential effects on antimicrobial performance and microbial susceptibility. However, more extensive testing is required to substantiate this. CONFLICT OF INTEREST: SLP is employed by Advanced Medical Solutions Ltd.

Microbiology of equine wounds and evidence of bacterial biofilms.

Horse wounds have a high risk of becoming infected due to their environment. Infected wounds harbour diverse populations of microorganisms, however in some cases these microorganisms can be difficult to identify and fail to respond to antibiotic treatment, resulting in chronic non-healing wounds. In human wounds this has been attributed to the ability of bacteria to survive in a biofilm phenotypic state. Biofilms are known to delay wound healing, principally due to their recalcitrance towards antimicrobial therapies and components of the innate immune response. This study describes the presence of bacterial biofilms within equine wounds. Thirteen 8-mm diameter tissue samples were collected from (n=18) chronic wounds. Following histological staining, samples were observed for evidence of biofilms. Fifty one wounds and control skin sites were sampled using sterile swabs. Control skin sites were on the uninjured side of the horse at the same anatomical location as the wound. The isolated bacteria were cultured aerobically and anaerobically. The biofilm forming potential of all the isolated bacteria was determined using a standard crystal violet microtitre plate assay. Stained tissue samples provided evidence of biofilms within 61.5% (8 out of 13) equine wounds. In total 340 bacterial isolates were identified from all the equine wound and skin samples. Pseudomonas aeruginosa and Enterococcus faecium were the most predominantly isolated bacterial species from equine wound and skin samples respectively. Staphylococcus was the most commonly isolated genus in both environments. Bacteria cultured from chronic and acute wounds showed significantly (P<0.05) higher biofilm forming potential than bacteria isolated from skin. This paper highlights preliminary evidence supporting the presence of biofilms and a high microbial diversity in equine chronic wounds. The presence of biofilms in equine wounds partly explains the reluctance of many lower limb wounds to heal. Non-healing limb wounds in horses are a well documented welfare and economic concern. This knowledge can be used to shape future treatments in order to increase the healing rate and decrease the costs and suffering associate with equine wounds.

A comparison of the antimicrobial efficacy of two silver-containing wound dressings on burn wound isolates.

OBJECTIVE: To evaluate and compare the efficacy of a silver alginate (SA) dressing and a silver carboxymethyl cellulose (SCMC) dressing on burn isolates grown within the quasi/non-biofilm state and the biofilm phenotypic states. METHOD: Antimicrobial activity was tested using 46 burn wound isolates with a corrected zone of inhibition (CZOI) assay on agar (quasi/non-biofilm) and poloxamer (biofilm). RESULTS: All Gram-negative and positive isolates evaluated were found to be sensitive to both silver containing wound dressings, although superior antimicrobial activity was observed for a select number of specific bacteria when grown in the quasi/non-biofilm phenotypic state, for the SCMC dressing. However, the majority of isolates demonstrated reduced sensitivity to silver when grown as a biofilm, compared with growth in the quasi/non-biofilm phenotypic state. Both dressings demonstrated equivalent antimicrobial activity on Gram-negative isolates grown in the biofilm phenotypic state. For the Gram-positive isolates growing in the biofilm phenotypic state, there appeared to be greater sensitivity to the SA dressing compared with the SCMC dressing, although this result was not statistically significant. CONCLUSION: This study demonstrated the antimicrobial effectiveness of an SA and SCMC dressing in inhibiting the growth of burn isolates residing in both the quasi/non-biofilm and biofilm phenotypic states. It also suggests the SA dressing could be more effective on Gram-positive isolates grown in the biofilm phenotypic state, compared with SCMC dressing.

Biofilms: possible strategies for suppression in chronic wounds.

Biofilms can delay wound healing significantly. The aim of this article is to highlight strategies that could be used to treat chronic wounds containing biofilms. Antibiofilm agents, their modes of action and efficacy in suppressing biofilms are discussed.

Prevalence of silver resistance genes in bacteria isolated from human and horse wounds.

The aim of this study was to investigate the prevalence of silver resistance genes in 172 bacterial strains which had been isolated from both human and equine wounds. PCR screening for 8 currently named genes in 3 silver resistance transcriptional units, silE, silRS and silP, silCBA and silF was performed on total DNA extracted from all clinical isolates. Plasmids were isolated from sil-positive strains to determine if the genes were present on the chromosome. MICs and zone of inhibition assays were utilised to examine phenotypic resistance to silver nitrate and ionic silver. Evidence of silver resistance genes was demonstrated in six strains of Enterobacter cloacae, an organism rarely implicated as a primary pathogen in chronic wounds. MIC data showed that all strains were inhibited at silver nitrate concentrations > or =5mg/L. When tested against a silver-containing absorbent wound dressing all strains showed inhibition of growth after 24h. In MIC and zone of inhibition studies, inhibition was evident but reduced in strains which contained sil genes. Although sil genes were found in six of the wound isolates studied, the genes were consistently associated with a non-pathogenic bacterium. Furthermore, investigation of phenotypic resistance in sil-positive isolates showed that silver continued to be effective.

Biofilms in wounds: management strategies.

Biofilms probably induce a chronic and/or 'quiet' inflammation in the chronic wound and so delay healing. This paper reviews current strategies that can be used to suppress biofilms in chronic wounds until better options are available.

Intravascular catheters and biofilm control.

Intravascular catheters are the most common cause of nosocomially acquired bloodstream infections. Bacteria found adhering to the intraluminal surfaces of catheters are the principal source and cause of these infections. Adherent bacteria overtime are known to form multicellular communities which become encased within a three dimensional matrix of extracellular polymeric material known as biofilms, which are thought to be responsible for persistent infections. Consequently, a number of technologies have been developed to help prevent and control biofilms in intravascular catheters. One such approach involves impregnating catheter material with antimicrobial agents. Unfortunately these methods are not universally effective in preventing catheter-related biofilm infections. Technologies that utilise antimicrobials, as catheter locks have been shown to have more potential for preventing biofilm formation and reducing the incidences of catheter related bloodstream infections (CRBSI). This article discusses the significance of biofilms in intravascular catheters and determines whether the treatments available today are proving to be effective for controlling biofilms and draws attention to future avenues which are being investigated to control biofilms and therefore CRBSI.

Biofilms and their relevance to veterinary medicine.

Bacteria are renowned for their ability to tolerate and adapt to a wide range of adverse environmental conditions. The primary mechanism that facilitates these adaptations is thought to be the capacity to form and maintain biofilms. Within a biofilm, bacteria become attached to a surface where they exist in complex communities which are able to interact with each other through intracellular communication and thus rapidly adapt to changing environments. The organisms within biofilms are notorious for their resistance towards the host immune response and antibacterial agents compared to their free-living planktonic counterparts. Consequently, biofilms are of significant importance to both clinical and veterinary science. However, although bacterial infections are widely reported in animals their association with biofilms is rarely discussed. The aim of this review is to look at the characteristics of biofilm infections in humans and to relate this knowledge to veterinary science in order to assess their relevance in this area.

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.

Use of in vivo-generated biofilms from hemodialysis catheters to test the efficacy of a novel antimicrobial catheter lock for biofilm eradication in vitro.

This biofilm study was conducted to assess the in vitro activity of tetrasodium EDTA on catheters that had been routinely removed from hemodialysis patients at Leeds Teaching Hospitals Trust due to maturation of fistula. Catheters were screened by culture of through-catheter flush, and isolates were identified by standard methodologies; 20 isolates were found to be biofilm positive. Initial biofilm cell count levels averaged above 10(5) CFU/1-cm catheter section. Bacteria identified in the biofilms were gram-negative (1 isolate), gram-positive (11 isolates), or mixed species (8 isolates). After a 24-h lock, 40 mg of tetrasodium EDTA per ml was effective at eradicating the total biofilm viable count in almost all cases. The efficacy of tetrasodium EDTA as a catheter lock potentially shows that this agent could substantially reduce catheter-related infections and be used to treat patients with limited access.