Invasive Candidiasis in Patients with Implants

Implantable device infections are an important cause of invasive candidiasis and carry high rates of morbidity and mortality. Central vascular access catheters are by far the most commonly infected type of device. Infections associated with peritoneal dialysis catheters, cardiac devices, prosthetic joints, and other implantable devices are much less common but can have devastating consequences for affected patients. Central to the pathogenesis of these infections is the interplay between altered anatomic barriers due to device implantation, host immune factors, and the tendency of Candida to form biofilms upon inanimate surfaces. Once infection develops, current treatment options nearly always necessitate removal of the device, so major efforts are under way to prevent infection by implementing innovative infection control strategies and developing implants that are less susceptible to biofilm formation. This review focuses on recent developments in our understanding of the epidemiology, pathogenesis, treatment options, and prevention of implant-associated invasive candidiasis.     

On-demand release of Candida albicans biofilms from urinary catheters by mechanical surface deformation

Abstract

Candida albicans is a leading cause of catheter-associated urinary tract infections and elimination of these biofilm-based infections without antifungal agents would constitute a significant medical advance. A novel urinary catheter prototype that utilizes on-demand surface deformation is effective at eliminating bacterial biofilms and here the broader applicability of this prototype to remove fungal biofilms has been demonstrated. C. albicans biofilms were debonded from prototypes by selectively inflating four additional intralumens surrounding the main lumen of the catheters to provide the necessary surface strain to remove the adhered biofilm. Deformable catheters eliminated significantly more biofilm than the controls (>90% eliminated vs 10% control; p < 0.001). Mechanical testing revealed that fungal biofilms have an elastic modulus of 45 ± 6.7 kPa with a fracture energy of 0.4–2 J m^?2. This study underscores the potential of mechanical disruption as a materials design strategy to combat fungal device-associated infections.     

Biofilm formation of Klebsiella pneumoniae on urethral catheters requires either type 1 or type 3 fimbriae

Urinary catheters are standard medical devices utilized in both hospital and nursing home settings, but are associated with a high frequency of catheter-associated urinary tract infections (CAUTI). In particular, biofilm formation on the catheter surface by uropathogens such as Klebsiella pneumoniae causes severe problems. Here we demonstrate that type 1 and type 3 fimbriae expressed by K.?pneumoniae enhance biofilm formation on urinary catheters in a catheterized bladder model that mirrors the physico-chemical conditions present in catheterized patients. Furthermore, we show that both fimbrial types are able to functionally compensate for each other during biofilm formation on urinary catheters. In situ monitoring of fimbrial expression revealed that neither of the two fimbrial types is expressed when cells are grown planktonically. Interestingly, during biofilm formation on catheters, both fimbrial types are expressed, suggesting that they are both important in promoting biofilm formation on catheters. Additionally, transformed into and expressed by a nonfimbriated Escherichia coli strain, both fimbrial types significantly increased biofilm formation on catheters compared with the wild-type E.?coli strain. The widespread occurrence of the two fimbrial types in different species of pathogenic bacteria stresses the need for further assessment of their role during urinary tract infections.     

Identification of small molecules inhibiting diguanylate cyclases to control bacterial biofilm development

Biofilm formation by pathogenic bacteria is an important virulence factor in the development of numerous chronic infections, thereby causing a severe health burden. Many of these infections cannot be resolved, as bacteria in biofilms are resistant to the host’s immune defenses and antibiotic therapy. An urgent need for new strategies to treat biofilm-based infections is critically needed. Cyclic di-GMP (c-di-GMP) is a widely conserved second-messenger signal essential for biofilm formation. The absence of this signalling system in higher eukaryotes makes it an attractive target for the development of new anti-biofilm agents. In this study, the results of an in silico pharmacophore-based screen to identify small-molecule inhibitors of diguanylate cyclase (DGC) enzymes that synthesize c-di-GMP are described. Four small molecules, LP 3134, LP 3145, LP 4010 and LP 1062 that antagonize these enzymes and inhibit biofilm formation by Pseudomonas aeruginosa and Acinetobacter baumannii in a continuous-flow system are reported. All four molecules dispersed P. aeruginosa biofilms and inhibited biofilm development on urinary catheters. One molecule dispersed A. baumannii biofilms. Two molecules displayed no toxic effects on eukaryotic cells. These molecules represent the first compounds identified from an in silico screen that are able to inhibit DGC activity to prevent biofilm formation.     

Human cathelicidin peptide LL37 inhibits both attachment capability and biofilm formation of Staphylococcus epidermidis

Aims: The aim of this work was to investigate the possible effect of human cathelicidin antimicrobial peptide LL37 on biofilm formation of Staphylococcus epidermidis, a major causative agent of indwelling device‐related infections. Methods and Results: We performed initial attachment assay and biofilm formation solid surface assay in microtitre plates, as well as growth experiment in liquid medium using laboratory strain Staph. epidermidis ATCC35984. We found that already a low concentration of the peptide LL37 (1 mg l^?1) significantly decreased both the attachment of bacteria to the surface and also the biofilm mass. No growth inhibition was observed even at 16 mg l^?1 concentration of LL37, indicating a direct effect of the peptide on biofilm production. Conclusions: As biofilm protects bacteria during infections in humans and allows their survival in a hostile environment, inhibition of biofilm formation by LL37 may have a key role to prevent bacterial colonization on indwelling devices. Significance and Impact of the Study: Our findings suggest that this host defence factor can be a potential candidate in prevention and treatment strategies of Staph. epidermidis infections in humans.     

Update on the challenging role of biofilms in peritoneal dialysis

Biofilms are commonly associated with an increased risk of patient infection. In peritoneal dialysis (PD), catheter associated infection, especially peritonitis, remains a clinically relevant problem. Although the presence of a biofilm is recognized in relapsing, repeat, and catheter-related peritonitis, it remains poorly characterized. In this review, an update on the role of biofilms in PD infections is presented. The emerging concept that host cells and tissue associated biofilms, in addition to the biofilms on the catheters themselves, contribute to the recalcitrance of infections is discussed. Furthermore, the evidence of biofilms on PD catheters, their developmental stages, and the possible influence of the PD environment are reviewed. The focus is given to ex vivo and in vitro studies that contribute to the elucidation of the interplay between host, microbial, and dialysis factors. The key issues that are still to be answered and the challenges to clinical practice are discussed.     

Surface Acoustic Waves Enhance Neutrophil Killing of Bacteria

Biofilms are structured communities of bacteria that play a major role in the pathogenicity of bacteria and are the leading cause of antibiotic resistant bacterial infections on indwelling catheters and medical prosthetic devices. Failure to resolve these biofilm infections may necessitate the surgical removal of the prosthetic device which can be debilitating and costly. Recent studies have shown that application of surface acoustic waves to catheter surfaces can reduce the incidence of infections by a mechanism that has not yet been clarified. We report here the effects of surface acoustic waves (SAW) on the capacity of human neutrophils to eradicate S. epidermidis bacteria in a planktonic state and within biofilms. Utilizing a novel fibrin gel system that mimics a tissue-like environment, we show that SAW, at an intensity of 0.3 mW/cm², significantly enhances human neutrophil killing of S. epidermidis in a planktonic state and within biofilms by enhancing human neutrophil chemotaxis in response to chemoattractants. In addition, we show that the integrin CD18 plays a significant role in the killing enhancement observed in applying SAW. We propose from out data that this integrin may serve as mechanoreceptor for surface acoustic waves enhancing neutrophil chemotaxis and killing of bacteria.     

A Candida albicans early stage biofilm detachment event in rich medium

Background  

Dispersal from Candida albicans biofilms that colonize catheters is implicated as a primary factor in the link between contaminated catheters and life threatening blood stream infections (BSI). Appropriate in vitro C. albicans biofilm models are needed to probe factors that induce detachment events.     

Role of type 1 and type 3 fimbriae in <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> biofilm formation

Background  

Klebsiella pneumoniae is an important gram-negative opportunistic pathogen causing primarily urinary tract infections, respiratory infections, and bacteraemia. The ability of bacteria to form biofilms on medical devices, e.g. catheters, has a major role in development of many nosocomial infections. Most clinical K. pneumoniae isolates express two types of fimbrial adhesins, type 1 fimbriae and type 3 fimbriae. In this study, we characterized the role of type 1 and type 3 fimbriae in K. pneumoniae biofilm formation.     

Specific selection for virulent urinary tract infectious Escherichia coli strains during catheter-associated biofilm formation

Biofilm-associated bacterial infections have a major impact on artificial implants such as urinary catheters, often with devastating consequences. The capacity of a microorganism to form a biofilm on a surface depends on the nature of the surface and its conditioning. When a urinary catheter is exposed to urine, various components adsorb onto the surface and form a conditioning film, which becomes the real interface where microbial interaction takes place. It follows that the material constituting the catheter determines the composition of the conditioning film, which in turn influences which microorganisms can attach. Urinary tract infectious (UTI) Escherichia coli range in pathogenicity and the damage they cause--from benign asymptomatic bacteriuria (ABU) strains, which inflict no or few problems to the host, to uropathogenic E. coli (UPEC) strains, which are virulent and often cause severe symptoms and complications. We have found that whereas ABU strains produce better biofilms on polystyrene and glass, UPEC strains have a clear competitive advantage during biofilm growth on catheter surfaces. Our results indicate that some silicone and silicone-latex catheters actually select for and promote biofilm formation of the most virulent group of UTI E. coli strains, hardly a desirable situation for the catheterized patient.     

A dynamic in vitro model for evaluating antimicrobial activity against bacterial biofilms using a new device and clinical-used catheters

The activity of daptomycin compared to vancomycin against Staphylococcus epidermidis-biofilms on intravascular catheters has been evaluated using the new Sevilla device that enables to use medical grade-catheters, in an in vitro model that simulates the in vivo conditions. S. epidermidis-biofilms were obtained on polyurethane catheter segments using the Sevilla device linked to a continuous culture system for 24 h. To assess the antimicrobial activity, at this time the continuous culture system was changed to therapeutic antimicrobial concentration solutions for 48 h. At each 24 h interval time, catheter segments were taken out, washed and sonicated. Viable adherent bacteria were determined by agar plating. Data of surviving bacteria numbers attached to the catheter surface obtained with the Sevilla device showed a very good reproducibility. Daptomycin showed a good activity against S. epidermidis-biofilm on polyurethane catheter surface. After 48 h exposure to daptomycin, surviving adherent bacteria were reduced by 4 log compared to the control with no antimicrobial. Using the same model, vancomycin reduced bacterial survival by only 1.3 log. The Sevilla device enables antimicrobial agent activity against bacterial biofilms grown on the external surface of catheters used in clinical practice to be evaluated. The model used replicates as closely as possible the biofilm formed in a highly standardized way. Using this model, daptomycin demonstrates potent in vitro activity against S. epidermidis-biofilm on a polyurethane catheter; this activity was greater than that showed by vancomycin.     

In vitro Activity of Daptomycin,Linezolid and Rifampicin on <Emphasis Type="Italic">Staphylococcus epidermidis</Emphasis> Biofilms

Owing to their massive use, Staphylococcus epidermidis has recently developed significant resistance to several antibiotics, and became one of the leading causes of hospital-acquired infections. Current antibiotics are typically ineffective in the eradication of bacteria in biofilm-associated persistent infections. Accordingly, the paucity of effective treatment against cells in this mode of growth is a key factor that potentiates the need for new agents active in the prevention or eradication of biofilms. Daptomycin and linezolid belong to the novel antibiotic therapies that are active against gram-positive cocci. On the other hand, rifampicin has been shown to be one of the most potent, prevalent antibiotics against S. epidermidis biofilms. Therefore, the main aim of this study was to study the susceptibility of S. epidermidis biofilm cells to the two newer antimicrobial agents previously mentioned, and compare the results obtained with the antimicrobial effect of rifampicin, widely used in the prevention/treatment of indwelling medical device infections. To this end the in vitro activities of daptomycin, linezolid, and rifampicin on S. epidermidis biofilms were accessed, using these antibiotics at MIC and peak serum concentrations. The results demonstrated that at MIC concentration, rifampicin was the most effective antibiotic tested. At peak serum concentration, both strains demonstrated similar susceptibility to rifampicin and daptomycin, with colony-forming units (CFUs) reductions of approximately 3–4 log₁₀, with a slightly lower response to linezolid, which was also more strain dependent. However, considering all the parameters studied, daptomycin was considered the most effective antibiotic tested, demonstrating an excellent in vitro activity against S. epidermidis biofilm cells. In conclusion, this antibiotic can be strongly considered as an acceptable therapeutic option for S. epidermidis biofilm-associated infections and can represent a potential alternative to rifampicin in serious infections where rifampicin resistance becomes prevalent.     

Polymer Designs to Control Biofilm Growth on Medical Devices

Indwelling and temporary medical delivery devices (i.e. catheters) are increasingly used in hospital settings, providing clinicians with useful tools to administer nutrients, draw blood samples and deliver drugs. However, they can often put patients at risk for local or systemic infections, including bloodstream infections and endocarditis. Microorganisms readily adhere to the surfaces and colonize them by forming a slimy layer of biofilm. Bacteria growing in biofilms exhibit an increased antibiotic resistance in comparison with planktonic cells. Consequently the antibiotic treatment of these medical device-associated infections frequently fails. Detechment resulting in the formation of microemboli is a further biofilm related complication. Since infections often involve increased morbidity and morality, prolonged hospitalization and additional medical costs, various strategies to prevent biofilm formation on implanted medical devices have been developed over the last two decades. In this paper we review and discuss the most significant experimental approaches to inhibit bacterial adhesion and growth on these devices.     

Biofilms in device-related infections

The use of various medical devices including indwelling vascular catheters, cardiac pacemakers, prosthetic heart valves, chronic ambulatory peritoneal dialysis catheters and prosthetic joints has greatly facilitated the management of serious medical and surgical illness. However, the successful development of synthetic materials and introduction of these artificial devices into various body systems has been accompanied by the ability of microorganisms to adhere to these devices in the environment of biofilms that protect them from the activity of antimicrobial agents and from host defense mechanisms. A number of host, biomaterial and microbial factors are unique to the initiation, persistence and treatment failures of device-related infections. Intravascular catheters are the most common devices used in clinical practice and interactions associated with these devices are the leading cause of nosocomial bacteremias. The infections associated with these devices include insertion site infection, septic thrombophlebitis, septicemia, endocarditis and metastatic abscesses. Other important device-related infections include infections of vascular prostheses, intracardiac prostheses, total artificial hearts, indwelling urinary catheters, orthopedic prostheses, endotracheal tubes and extended wear lenses. The diagnosis and management of biofilm-associated infections remain difficult but critical issues. Appropriate antimicrobial therapy is often not effective in eradicating these infections and the removal of the device becomes necessary. Several improved diagnostic and therapeutic modalities have been reported in recent experimental studies. The clinical usefulness of these strategies remains to be determined.     

Virulence factors in Proteus bacteria from biofilm communities of catheter-associated urinary tract infections

More than 40% of nosocomial infections are those of the urinary tract, most of these occurring in catheterized patients. Bacterial colonization of the urinary tract and catheters results not only in infection, but also various complications, such as blockage of catheters with crystalline deposits of bacterial origin, generation of gravels and pyelonephritis. The diversity of the biofilm microbial community increases with duration of catheter emplacement. One of the most important pathogens in this regard is Proteus mirabilis. The aims of this study were to identify and assess particular virulence factors present in catheter-associated urinary tract infection (CAUTI) isolates, their correlation and linkages: three types of motility (swarming, swimming and twitching), the ability to swarm over urinary catheters, biofilm production in two types of media, urease production and adherence of bacterial cells to various types of urinary tract catheters. We examined 102 CAUTI isolates and 50 isolates taken from stool samples of healthy people. Among the microorganisms isolated from urinary catheters, significant differences were found in biofilm-forming ability and the swarming motility. In comparison with the control group, the microorganisms isolated from urinary catheters showed a wider spectrum of virulence factors. The virulence factors (twitching motility, swimming motility, swarming over various types of catheters and biofilm formation) were also more intensively expressed.     

左氧氟沙星浸涂导管对铜绿假单胞菌生物膜的影响

目的评估左氧氟沙星（levofloxacin,LFX）浸涂导管抑制铜绿假单胞菌粘附、定植,防止生物膜形成的能力。方法体外部分：制备LFX浸涂导管。LFX浸涂导管、PVC导管分别浸没在5 mL 50%LB培养液中（含PAO1 108CFU/mL）,37℃孵育6、12、24和48 h,在各时间点,予导管表面和导管培养液进行细菌计数。体内部分：小鼠皮下植入LFX浸涂导管或PVC导管,沿着导管注射PAO1菌液50μL（107CFU）。第1、5天,对植入导管及导管周围组织进行细菌计数及扫描电镜（SEM）观察。结果 （1）LFX浸涂导管显示药物的快速释放。（2）在各孵育时间点,LFX浸涂导管及导管培养液的细菌数较PVC导管均明显减少（P〈0.05）。（3）小鼠感染第1、5天,LFX浸涂植入导管表面没有或很少细菌;LFX浸涂导管较PVC导管能明显减少植入导管周围组织的细菌量（P〈0.05）。（4）SEM观察：感染第1、5天,LFX浸涂导管表面散在单个细菌或者没有细菌;而第1天,PVC导管表面大量细菌分散存在。第5天,导管表面＂珊瑚状＂生物膜形成。结论 LFX浸涂导管能抑制铜绿假单胞菌粘附、定植,防止生物膜形成,从而有效降低导管生物膜相关感染的发生。     

Susceptibility of staphylococcal biofilms to enzymatic treatments depends on their chemical composition

Bacterial infections are serious complications after orthopaedic implant surgery. Staphylococci, with Staphylococcus epidermidis as a leading species, are the prevalent and most important species involved in orthopaedic implant-related infections. The biofilm mode of growth of these bacteria on an implant surface protects the organisms from the host’s immune system and from antibiotic therapy. Therapeutic agents that disintegrate the biofilm matrix would release planktonic cells into the environment and therefore allow antibiotics to eliminate the bacteria. An addition of a biofilm-degrading agent to a solution used for washing–draining procedures of infected orthopaedic implants would greatly improve the efficiency of the procedure and thus help to avoid the removal of the implant. We have previously shown that the extracellular staphylococcal matrix consists of a poly-N-acetylglucosamine (PNAG), extracellular teichoic acids (TAs) and protein components. In this study, we accessed the sensitivity of pre-formed biofilms of five clinical staphylococcal strains associated with orthopaedic prosthesis infections and with known compositions of the biofilm matrix to periodate, Pectinex Ultra SP, proteinase K, trypsin, pancreatin and dispersin B, an enzyme with a PNAG-hydrolysing activity. We also tested the effect of these agents on the purified carbohydrate components of staphylococcal biofilms, PNAG and TA. We found that the enzymatic detachment of staphylococcal biofilms depends on the nature of their constituents and varies between the clinical isolates. We suggest that a treatment with dispersin B followed by a protease (proteinase K or trypsin) could be capable to eradicate biofilms of a variety of staphylococcal strains on inert surfaces.     

Biofilm: set-up and organization of a bacterial community

Bacterial attachment on various surfaces mostly takes place in the form of specialised bacterial communities, referred to as biofilm. The biofilm is formed through series of interactions between cells and adherence to surface, resulting in an organised structure. In this review we have been using Pseudomonas aeruginosa as a model microorganism to describe the series of events that occurred during this developmental process. P. aeruginosa is an opportunistic pathogen that has a wide variety of hosts and infectious sites. In addition to biofilm formation in certain tissues, inert surfaces, such as catheters, are also target for bacterial biofilm development. The use of convenient genetic screens has made possible the identification of numerous biofilm-defective mutants, which have been characterised further. These studies have allowed the proposal for a global model, in which key events are described for the different stages of biofilm formation. Briefly, flagellar mobility is crucial for approaching the surface, whereas type IV pili motility is preponderant for surface colonisation and microcolonies formation. These microcolonies are finally packed together and buried in an exopolysaccharide matrix to form the differentiated bio-film. It is obvious that the different stages of biofilm formation also involved perception of environmental stimuli. These stimuli, and their associated complex regulatory networks, have still to be fully characterised to understand the bacterial strategy, which initiates biofilm formation. One such regulatory system, called Quorum sensing, is one of the key player in the initial differentiation of biofilm. Finally, a better understanding, at the molecular level, of biofilm establishment and persistence should help for the design of antimicrobials that prevent bacterial infections.