New polymer-antibiotic systems to inhibit bacterial biofilm formation: a suitable approach to prevent central venous catheter-associated infections

An Overview of Biofilm Formation-Combating Strategies and Mechanisms of Action of Antibiofilm Agents

Biofilm formation on surfaces via microbial colonization causes infections and has become a major health issue globally. The biofilm lifestyle provides resistance to environmental stresses and antimicrobial therapies. Biofilms can cause several chronic conditions, and effective treatment has become a challenge due to increased antimicrobial resistance. Antibiotics available for treating biofilm-associated infections are generally not very effective and require high doses that may cause toxicity in the host. Therefore, it is essential to study and develop efficient anti-biofilm strategies that can significantly reduce the rate of biofilm-associated healthcare problems. In this context, some effective combating strategies with potential anti-biofilm agents, including plant extracts, peptides, enzymes, lantibiotics, chelating agents, biosurfactants, polysaccharides, organic, inorganic, and metal nanoparticles, etc., have been reviewed to overcome biofilm-associated healthcare problems. From their extensive literature survey, it can be concluded that these molecules with considerable structural alterations might be applied to the treatment of biofilm-associated infections, by evaluating their significant delivery to the target site of the host. To design effective anti-biofilm molecules, it must be assured that the minimum inhibitory concentrations of these anti-biofilm compounds can eradicate biofilm-associated infections without causing toxic effects at a significant rate.

Antimicrobial Peptides as an Alternative for the Eradication of Bacterial Biofilms of Multi-Drug Resistant Bacteria

Bacterial resistance is an emergency public health problem worldwide, compounded by the ability of bacteria to form biofilms, mainly in seriously ill hospitalized patients. The World Health Organization has published a list of priority bacteria that should be studied and, in turn, has encouraged the development of new drugs. Herein, we explain the importance of studying new molecules such as antimicrobial peptides (AMPs) with potential against multi-drug resistant (MDR) and extensively drug-resistant (XDR) bacteria and focus on the inhibition of biofilm formation. This review describes the main causes of antimicrobial resistance and biofilm formation, as well as the main and potential AMP applications against these bacteria. Our results suggest that the new biomacromolecules to be discovered and studied should focus on this group of dangerous and highly infectious bacteria. Alternative molecules such as AMPs could contribute to eradicating biofilm proliferation by MDR/XDR bacteria; this is a challenging undertaking with promising prospects.

1-Amino-2'-fucosyllactose inhibits biofilm formation by Streptococcus agalactiae

2'-Fucosyllactose (2'-FL) is a ubiquitous oligosaccharide in human milk. Importantly, this carbohydrate promotes the growth of several strains of Bifidobacteria, a class of beneficial gut commensal, and inhibits epithelial binding of pathogens. In light of these protective effects, we elected to evaluate the potential of 2'-FL to serve as an antibacterial agent against Group B Streptococcus (GBS). While 2'-FL was devoid of any substantial antimicrobial or antibiofilm activity, conversion of 2'-FL to its reducing end β-amine provided a novel antibiofilm compound.

Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action

Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC₅₀) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.

Treatment of osteomyelitis defects by a vancomycin-loaded gelatin/β-tricalcium phosphate composite scaffold

OBJECTIVE

In the present study, we aimed to assess whether gelatin/β-tricalcium phosphate (β-TCP) composite porous scaffolds could be used as a local controlled release system for vancomycin. We also investigated the efficiency of the scaffolds in eliminating infections and repairing osteomyelitis defects in rabbits.

METHODS

The gelatin scaffolds containing differing amounts of of β-TCP (0%, 10%, 30% and 50%) were prepared for controlled release of vancomycin and were labelled G-TCP0, G-TCP1, G-TCP3 and G-TCP5, respectively. The Kirby-Bauer method was used to examine the release profile. Chronic osteomyelitis models of rabbits were established. After thorough debridement, the osteomyelitis defects were implanted with the scaffolds. Radiographs and histological examinations were carried out to investigate the efficiency of eliminating infections and repairing bone defects.

RESULTS

The prepared gelatin/β-TCP scaffolds exhibited a homogeneously interconnected 3D porous structure. The G-TCP0 scaffold exhibited the longest duration of vancomycin release with a release duration of eight weeks. With the increase of β-TCP contents, the release duration of the β-TCP-containing composite scaffolds was decreased. The complete release of vancomycin from the G-TCP5 scaffold was achieved within three weeks. In the treatment of osteomyelitis defects in rabbits, the G-TCP3 scaffold showed the most efficacious performance in eliminating infections and repairing bone defects.

CONCLUSIONS

The composite scaffolds could achieve local therapeutic drug levels over an extended duration. The G-TCP3 scaffold possessed the optimal porosity, interconnection and controlled release performance. Therefore, this scaffold could potentially be used in the treatment of chronic osteomyelitis defects.Cite this article: J. Zhou, X. G. Zhou, J. W. Wang, H. Zhou, J. Dong. Treatment of osteomyelitis defects by a vancomycin-loaded gelatin/β-tricalcium phosphate composite scaffold. Bone Joint Res 2018;7:46-57. DOI: 10.1302/2046-3758.71.BJR-2017-0129.R2.

Antifouling and antimicrobial biomaterials: an overview

The use of implantable medical devices is a common and indispensable part of medical care for both diagnostic and therapeutic purposes. However, as side effect, the implant of medical devices quite often leads to the occurrence of difficult-to-treat infections, as a consequence of the colonization of their abiotic surfaces by biofilm-growing microorganisms increasingly resistant to antimicrobial therapies. A promising strategy to combat device-related infections is based on anti-infective biomaterials that either repel microbes, so they cannot attach to the device surfaces, or kill them in the surrounding areas. In general, such biomaterials are characterized by antifouling coatings, exhibiting low adhesion or even repellent properties towards microorganisms, or antimicrobial coatings, able to kill microbes approaching the surface. In this light, the present overview will address the development in the last two decades of antifouling and antimicrobial biomaterials designed to potentially limit the initial stages of microbial adhesion, as well as the microbial growth and biofilm formation on medical device surfaces.

Current Trends in Development of Liposomes for Targeting Bacterial Biofilms

Biofilm targeting represents a great challenge for effective antimicrobial therapy. Increased biofilm resistance, even with the elevated concentrations of very potent antimicrobial agents, often leads to failed therapeutic outcome. Application of biocompatible nanomicrobials, particularly liposomally-associated nanomicrobials, presents a promising approach for improved drug delivery to bacterial cells and biofilms. Versatile manipulations of liposomal physicochemical properties, such as the bilayer composition, membrane fluidity, size, surface charge and coating, enable development of liposomes with desired pharmacokinetic and pharmacodynamic profiles. This review attempts to provide an unbiased overview of investigations of liposomes destined to treat bacterial biofilms. Different strategies including the recent advancements in liposomal design aiming at eradication of existing biofilms and prevention of biofilm formation, as well as respective limitations, are discussed in more details.

Wild mushroom extracts as inhibitors of bacterial biofilm formation

Microorganisms can colonize a wide variety of medical devices, putting patients in risk for local and systemic infectious complications, including local-site infections, catheter-related bloodstream infections, and endocarditis. These microorganisms are able to grow adhered to almost every surface, forming architecturally complex communities termed biofilms. The use of natural products has been extremely successful in the discovery of new medicine, and mushrooms could be a source of natural antimicrobials. The present study reports the capacity of wild mushroom extracts to inhibit in vitro biofilm formation by multi-resistant bacteria. Four Gram-negative bacteria biofilm producers (Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, and Acinetobacter baumannii) isolated from urine were used to verify the activity of Russula delica, Fistulina hepatica, Mycena rosea, Leucopaxilus giganteus, and Lepista nuda extracts. The results obtained showed that all tested mushroom extracts presented some extent of inhibition of biofilm production. Pseudomonas aeruginosa was the microorganism with the highest capacity of biofilm production, being also the most susceptible to the extracts inhibition capacity (equal or higher than 50%). Among the five tested extracts against E. coli, Leucopaxillus giganteus (47.8%) and Mycenas rosea (44.8%) presented the highest inhibition of biofilm formation. The extracts exhibiting the highest inhibitory effect upon P. mirabilis biofilm formation were Sarcodon imbricatus (45.4%) and Russula delica (53.1%). Acinetobacter baumannii was the microorganism with the lowest susceptibility to mushroom extracts inhibitory effect on biofilm production (highest inhibition—almost 29%, by Russula delica extract). This is a pioneer study since, as far as we know, there are no reports on the inhibition of biofilm production by the studied mushroom extracts and in particular against multi-resistant clinical isolates; nevertheless, other studies are required to elucidate the mechanism of action.

Efficacy evaluation of antimicrobial drug-releasing polymer matrices

To assay in vitro antimicrobial activity of substances such as antibiotics or antiseptics, standard methods both in liquid and on solid media are available. These procedures cannot be adequate for testing antimicrobial-releasing or biocidal polymer systems.This chapter is focused on the description of methods that the authors have developed to evaluate the antimicrobial activity of either antimicrobial agent-releasing polymers or biocidal polymers. These assays can be applied to different types of water-soluble or insoluble polymer matrices.

Polyurethanes Loaded with Antibiotics: Influence of Polymer-Antibiotic Interactions onIn VitroActivity AgainstStaphylococcus epidermidis

Acidic or basic polyurethanes were loaded with antibiotics to develop materials to prevent medical device-related infections. A correlation between polymer-antibiotic interactions and amount of drug absorbed by polymers and released over time was found. Since the employed antibiotics, i.e. amoxicillin, cefamandole nafate, rifampin and vancomycin, possessed at least an acidic group in their structural formula, the introduction of basic tertiary amines in the polyurethane side-chain resulted in an increased polymer ability to adsorb antibiotics. However, a stronger ionic interaction between this polymer and the antibiotics caused a release of lower amount of drug over time. Antibiotics released from polymers inhibited Staphylococcus epidermidis growth on agar. Antibiotic-loaded polyurethanes kept in water for increasing times were still able to show inhibition zones of bacterial growth. The antibacterial activity lasted up to 3 hours for amoxicillin, 24 hours for vancomycin, 8 days for cefamandole nafate and 8 months for rifampin.

The controlled release of vancomycin in gelatin/β-TCP composite scaffolds

Osteomyelitis remains a difficult infection to treat for orthopaedic surgeons regardless of the continuous advances in surgical techniques and antimicrobial agents. The controlled release of vancomycin from local delivery system is a promising method for eliminating infection. In this study, biodegradable gelatin sponge containing different contents of β-tricalcium phosphate ceramic (β-TCP) was prepared for the controlled-release of vancomycin. We aimed to confirm the composite scaffolds could be used as a vancomycin sustained-release system. Examinations of scanning electron microscopy, Fourier transform infrared spectroscopy, mechanical properties, and in vivo drug release were performed. The results showed that the composite scaffolds could achieve local therapeutic drug levels over an extended duration. Taking consideration of porosity, interconnection, mechanical properties, and controlled release performance, the composite gelatin scaffold containing 30% β-TCP granules may be a good candidate for the controlled release of vancomycin in the treatment of chronic osteomyelitis.

Inhibitory activity of Fe(3) O(4)/oleic acid/usnic acid-core/shell/extra-shell nanofluid on S. aureus biofilm development

Undesired biofilm development is a major concern in many areas, especially in the medical field. The purpose of the present study was to comparatively investigate the antibiofilm efficacy of usnic acid, in soluble versus nanofluid formulation, in order to highlight the potential use of Fe(3) O(4)/oleic acid (FeOA) nanofluid as potential controlled release vehicle of this antibiofilm agent. The (+) -UA loaded into nanofluid exhibited an improved antibiofilm effect on S. aureus biofilm formation, revealed by the drastic decrease of the viable cell counts as well as by confocal laser scanning microscopy images. Our results demonstrate that FeOA nanoparticles could be used as successful coating agents for obtaining antibiofilm pellicles on different medical devices, opening a new perspective for obtaining new antimicrobial and antibiofilm surfaces, based on hybrid functionalized nanostructured biomaterials.

Anti-adhesion and antiproliferative cellulose triacetate membrane for prevention of biomaterial-centred infections associated with Staphylococcus epidermidis

The initial step in preventing biomaterial-associated infections consists of preventing bacterial adhesion to the device surface. One possible approach is the design of antibiotic-releasing biomaterials. Cellulose triacetate (CTA) membranes with the antibiotic imipenem (IPM) entrapped (CTA-IPM) were prepared. The material was characterised in terms of surface morphology by scanning electron microscopy, surface free energy of interaction and X-ray photoelectron spectroscopy (XPS). Antibiotic release studies were also performed. In vitro adhesion of Staphylococcus epidermidis RP62A to CTA-IPM was investigated using a modified microtitre plate assay, and the antibacterial activity of the CTA-IPM membrane was assessed by a modified Kirby-Bauer test, which showed effective entrapment of the antibiotic as confirmed by XPS and hydrophilicity assays. Release studies showed that this drug-polymer conjugate serves as an adequate reservoir for sustained release of IPM over a period of 71h at an effective bacteriostatic concentration. Moreover, bacterial adhesion tests showed a statistically significant decrease in the adhesion of S. epidermidis RP62A to CTA-IPM compared with its adhesion to CTA alone. The present innovative approach is capable of providing a membrane with anti-adhesive and antiproliferative properties, thus encouraging in vivo studies to provide a better simulation of the clinical situation.

Antimicrobial behavior of polyelectrolyte-surfactant thin film assemblies

Layer-by-layer (LbL) assembly, a technique that alternately deposites cationic and anionic materials, has proven to be a powerful technique for assembling thin films with a variety of properties and applications. The present work incorporates the antimicrobial agent cetyltrimethylammonium bromide (CTAB) in the cationic layer and uses poly(acrylic acid) (PAA) as the anionic layer. When the films are exposed to a humid environment, these agents diffuse out of the film, inhibiting bacterial growth in neighboring regions. Film growth, microstructure, and antimicrobial efficacy are studied here, with 10-bilayer films yielding thicknesses on the order of 2 microm. Various factors are shown to influence the antimicrobial efficacy including time, temperature, secondary ingredients, and number of bilayers. As more layers are deposited, antimicrobial efficacy is increased because more CTAB is able to diffuse throughout the film, and higher amounts of antimicrobials are released. Additionally, inclusion of the cationic poly(diallyldimethylammonium chloride) (PDDA) in the cationic layer in conjunction with CTAB increases film uniformity, and as a result, antimicrobial effectiveness is enhanced. These thin films provide the ability to render a surface antimicrobial and may be useful for bandages or sterilization of disposable objects (e.g., surgical marker).

Synthesis, characterization, andin vitro activity of antibiotic releasing polyurethanes to prevent bacterial resistance

Central venous catheters are a major cause of nosocomial bloodstream infections. Different attempts have been made to incorporate antimicrobial agents into catheters, particularly directed at the surface-coating of devices. To facilitate the antimicrobial adsorption, various cationic surfactants, which however showed several problems, have been used. On the other hand, impregnated catheters with only antimicrobials have demonstrated a short-term duration due to the difficulties to deliver the drug slowly. Thus, in order to obtain high antimicrobial-polymer affinity we synthesized or modified polyurethanes to introduce different functional groups. Polymers were loaded with two antibiotics, cefamandole nafate and rifampin (RIF), chosen for both their functional groups and their action spectrum. The in vitro release behavior showed that the elution of drugs depended on the matrix hydrophilicity and on the antibiotic-polymer and antibiotic-antibiotic interactions. To increase the amount of drug released, polyethylene glycol (PEG) used as a pore forming agent at different molecular weights was incorporated in the polymer bulk with antibiotics. As for the in vitro antimicrobial activity of matrices, assessed by Kirby-Bauer test, it was seen that antibiotics released from various formulations inhibited the bacterial growth and exerted a synergistic effect when both were present. In particular, PEG10000-containing polymer was active against the RIF-resistant S. aureus strain up to 23 days. These results suggest that the combined entrapping of antibiotics and pore formers in these novel polymer systems could be promising to prevent the bacterial colonization and to control the emergence of bacterial resistance.

Pore formers promoted release of an antifungal drug from functionalized polyurethanes to inhibit Candida colonization

AIMS

As a preventive strategy to inhibit fungal biofilm formation on medical devices, we planned experiments based on polyurethane loading with fluconazole plus pore-former agents in order to obtain a promoted release of the antifungal drug.

METHODS AND RESULTS

Different functional groups including carboxyl, hydroxyl, primary and tertiary amino groups, were introduced in polyurethanes. Fluconazole was adsorbed in higher amounts by the most hydrophilic polymers and its release was influenced by the degree of polymer swelling in water. The entrapping in the polymer of polyethylenglycol as a pore former significantly improved the fluconazole release while the entrapping of the higher molecular weight porogen albumin resulted in a controlled drug release and in an improved antifungal activity over time.

CONCLUSIONS

Among the tested in vitro models, best results were achieved with an hydrophobic polymer impregnated with 25% (w/w) albumin and fluconazole which inhibited Candida albicans growth and biofilm formation on polymeric surfaces up to 8 days.

SIGNIFICANCE AND IMPACT OF THE STUDY

The combined entrapping in polymers of pore formers and an antifungal drug and the consequent controlled release over time is a novel, promising approach in the development of medical devices refractory to fungal colonization.

Vascular Catheter-Related Infection and Sepsis

BACKGROUND

Catheter-related sepsis is a clinical syndrome characterized by the presence of a catheter-associated infection along with a systemic inflammatory response. The continual increase in the use of central venous catheters (CVCs) has been associated with a substantial risk of infectious complications that prolong the hospital stay and increase costs.

METHODS

The literature on CVCs was reviewed to determine the incidence of catheterrelated sepsis, its diagnosis, and the role of biofilms in pathogenesis.

RESULTS

The European Sepsis Group recently reported that 28% of CVC infections in intensive care unit patients were associated with sepsis, 24% with severe sepsis, and 30% with septic shock. Clinical diagnosis remains difficult. After CVC insertion, the intravascular portion of the device is covered rapidly by a thrombin layer, rich in host-derived proteins, that forms a conditioning film and promotes surface adherence of microbial colonizers. These microorganisms then enter their sessile mode of growth, secreting an exopolysaccharide slime within which organism density is regulated by quorum-sensing molecules. Microorganisms are dispersed in clumps that can become septic emboli. Antiadhesive, antiseptic, and antibiotic coatings of catheters have demonstrated only modest clinical efficacy.

CONCLUSION

Our group is involved in the design and in vitro assessment of new polymeric matrices for controlled release of antimicrobial molecules, and in comparative clinical studies of conventional versus antibiotic-coated or -impregnated catheters.

Emerging role of Enterococcus spp in catheter-related infections: biofilm formation and novel mechanisms of antibiotic resistance

Enterococci are gram-positive bacteria that are part of the normal human intestinal flora and can colonize the upper respiratory tract, biliary tract and vagina of otherwise healthy people. Although their virulence is relatively low, recently enterococci have emerged as significant nosocomial pathogens and are currently the 4th leading cause of hospital-acquired infections, including those associated with intravascular catheter and biliary stent implants. The frequent use of these medical devices is often associated with severe complications, including catheter-related bloodstream infections (CRBSIs) and biliary stent occlusions, because of microbial biofilm formation on the device surface. Furthermore, other than a high level of resistance to penicillin, ampicillin and aminoglycosides, a dramatic increase in vancomycin resistance of enterococci has been recently observed in most clinical settings. Clinical strains exhibiting novel mechanisms of acquired resistance to antimicrobials are frequently isolated. In addition, enterococci have a great ability to transmit these resistance traits to other species and even to other genera. Due to their associated morbidity and mortality, enterococcal infections related to medical devices currently represent a major challenge for clinicians, especially for the management of critically ill patients, resulting in prolonged hospitalization and additional health costs.

Modification of surface properties of biomaterials influences the ability of Candida albicans to form biofilms

Candida albicans biofilms form on indwelling medical devices (e.g., denture acrylic or intravenous catheters) and are associated with both oral and invasive candidiasis. Here, we determined whether surface modifications of polyetherurethane (Elasthane 80A [E80A]), polycarbonateurethane, and poly(ethyleneterephthalate) (PET) can influence fungal biofilm formation. Polyurethanes were modified by adding 6% polyethylene oxide (6PEO), 6% fluorocarbon, or silicone, while the PET surface was modified to generate hydrophilic, hydrophobic, cationic, or anionic surfaces. Formation of biofilm was quantified by determining metabolic activity and total biomass (dry weight), while its architecture was analyzed by confocal scanning laser microscopy (CSLM). The metabolic activity of biofilm formed by C. albicans on 6PEO-E80A was significantly reduced (by 78%) compared to that of biofilm formed on the nonmodified E80A (optical densities of 0.054 +/- 0.020 and 0.24 +/- 0.10, respectively; P = 0.037). The total biomass of Candida biofilm formed on 6PEO-E80A was 74% lower than that on the nonmodified E80A surface (0.46 +/- 0.15 versus 1.76 +/- 0.32 mg, respectively; P = 0.003). Fungal cells were easily detached from the 6PEO-E80A surface, and we were unable to detect C. albicans biofilm on this surface by CSLM. All other surface modifications allowed formation of C. albicans biofilm, with some differences in thearchitecture. Correlation between contact angle and biofilm formation was observed for polyetherurethane substrates (r = 0.88) but not for PET biomaterials (r = -0.40). This study illustrates that surface modification is a viable approach for identifying surfaces that have antibiofilm characteristics. Investigations into the clinical utility of the identified surfaces are warranted.

Infections associated with medical devices: pathogenesis, management and prophylaxis

The insertion or implantation of foreign bodies has become an indispensable part in almost all fields of medicine. However, medical devices are associated with a definitive risk of bacterial and fungal infections. Foreign body-related infections (FBRIs), particularly catheter-related infections, significantly contribute to the increasing problem of nosocomial infections. While a variety of micro-organisms may be involved as pathogens, staphylococci account for the majority of FBRIs. Their ability to adhere to materials and to promote formation of a biofilm is the most important feature of their pathogenicity. This biofilm on the surface of colonised foreign bodies is regarded as the biological correlative for the clinical experience with FBRI, that is, that the host defence mechanisms often seem to be unable to handle the infection and, in particular, to eliminate the micro-organisms from the infected device. Since antibacterial chemotherapy is also frequently not able to cure these infections despite the use of antibacterials with proven in vitro activity, removal of implanted devices is often inevitable and has been standard clinical practice. However, in specific circumstances, such as infections of implanted medical devices with coagulase-negative staphylococci, a trial of salvage of the device may be justified. All FBRIs should be treated with antibacterials to which the pathogens have been shown to be susceptible. In addition to systemic antibacterial therapy, an intraluminal application of antibacterial agents, referred to as the 'antibiotic-lock' technique, should be considered to circumvent the need for removal, especially in patients with implanted long-term catheters. To reduce the incidence of intravascular catheter-related bloodstream infections, specific guidelines comprising both technological and nontechnological strategies for prevention have been established. Quality assurance, continuing education, choice of the catheter insertion site, hand hygiene and aseptic techniques are aspects of particular interest. Furthermore, all steps in the pathogenesis of biofilm formation may represent targets against which prevention strategies may be directed. Alteration of the foreign body material surface may lead to a change in specific and nonspecific interactions with micro-organisms and, thus, to a reduced microbial adherence. Medical devices made out of a material that would be antiadhesive or at least colonisation resistant would be the most suitable candidates to avoid colonisation and subsequent infection. Another concept for the prevention of FBRIs involves the impregnation of devices with various substances such as antibacterials, antiseptics and/or metals. Finally, further studies are needed to translate the knowledge on the mechanisms of biofilm formation into applicable therapeutic and preventive strategies.

Usnic acid, a natural antimicrobial agent able to inhibit bacterial biofilm formation on polymer surfaces

In modern medicine, artificial devices are used for repair or replacement of damaged parts of the body, delivery of drugs, and monitoring the status of critically ill patients. However, artificial surfaces are often susceptible to colonization by bacteria and fungi. Once microorganisms have adhered to the surface, they can form biofilms, resulting in highly resistant local or systemic infections. At this time, the evidence suggests that (+)-usnic acid, a secondary lichen metabolite, possesses antimicrobial activity against a number of planktonic gram-positive bacteria, including Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. Since lichens are surface-attached communities that produce antibiotics, including usnic acid, to protect themselves from colonization by other bacteria, we hypothesized that the mode of action of usnic acid may be utilized in the control of medical biofilms. We loaded (+)-usnic acid into modified polyurethane and quantitatively assessed the capacity of (+)-usnic acid to control biofilm formation by either S. aureus or Pseudomonas aeruginosa under laminar flow conditions by using image analysis. (+)-Usnic acid-loaded polymers did not inhibit the initial attachment of S. aureus cells, but killing the attached cells resulted in the inhibition of biofilm. Interestingly, although P. aeruginosa biofilms did form on the surface of (+)-usnic acid-loaded polymer, the morphology of the biofilm was altered, possibly indicating that (+)-usnic acid interfered with signaling pathways.

Clinical review: new technologies for prevention of intravascular catheter-related infections

Intravascular catheters have become essential devices for the management of critically and chronically ill patients. However, their use is often associated with serious infectious complications, mostly catheter-related bloodstream infection (CRBSI), resulting in significant morbidity, increased duration of hospitalization, and additional medical costs. The majority of CRBSIs are associated with central venous catheters (CVCs), and the relative risk for CRBSI is significantly greater with CVCs than with peripheral venous catheters. However, most CVC-related infections are preventable, and different measures have been implemented to reduce the risk for CRBSI, including maximal barrier precautions during catheter insertion, catheter site maintenance, and hub handling. The focus of the present review is on new technologies for preventing infections that are directed at CVCs. New preventive strategies that have been shown to be effective in reducing risk for CRBSI, including the use of catheters and dressings impregnated with antiseptics or antibiotics, the use of new hub models, and the use of antibiotic lock solutions, are briefly described.