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.     

Patient's cells colonize the biofilm of Tenckhoff catheters used in peritoneal dialysis

Peritoneal dialysis (PD) is a renal substitutive therapy based on the infusion of a dialysate in the peritoneum, which induces through an osmotic gradient the ultrafiltration of water and the clearance of blood stream impurities by the peritoneal membrane. The colonization of Tenckhoff catheters (TCs) used in PD by pathogenic microorganisms can lead to peritonitis, and probably catheter removal. Here, optical microscopy and scanning electron microscopy were applied to study biofilm formation in 11 TCs. Biofilms varied in their morphology and thickness. Short-term catheters (6 months) presented thinner deposits (3 μm) with granular or flat morphologies, either on the intraluminal or external surfaces. Bacterial colonies were found on catheters from infected patients. A tendency was observed for long-term catheters (6–8 years) to present thicker biofilms (30–35 μm). Surprisingly, patients' cells colonized the deep layers of the thicker biofilms, forming a complex multicelullar community. It was concluded that the presence of a biofilm is not necessarily related with peritonitis, and biofilm features may correlate to the therapy time.     

Patient's cells colonize the biofilm of Tenckhoff catheters used in peritoneal dialysis

Peritoneal dialysis (PD) is a renal substitutive therapy based on the infusion of a dialysate in the peritoneum, which induces through an osmotic gradient the ultrafiltration of water and the clearance of blood stream impurities by the peritoneal membrane. The colonization of Tenckhoff catheters (TCs) used in PD by pathogenic microorganisms can lead to peritonitis, and probably catheter removal. Here, optical microscopy and scanning electron microscopy were applied to study biofilm formation in 11 TCs. Biofilms varied in their morphology and thickness. Short-term catheters (6 months) presented thinner deposits (3 μm) with granular or flat morphologies, either on the intraluminal or external surfaces. Bacterial colonies were found on catheters from infected patients. A tendency was observed for long-term catheters (6-8 years) to present thicker biofilms (30-35 μm). Surprisingly, patients' cells colonized the deep layers of the thicker biofilms, forming a complex multicelullar community. It was concluded that the presence of a biofilm is not necessarily related with peritonitis, and biofilm features may correlate to the therapy time.     

Fungal Biofilms in the Clinical Lab Setting

Device-related infections are often associated with biofilms (microbial communities encased within polysaccharide-rich extracellular matrix) formed by pathogens on surfaces of these devices. Candida species are the most common fungi isolated from infections associated with catheters and dentures, and both Candida and Fusarium are commonly isolated from contact lens–related infections such as fungal keratitis. These biofilms exhibit decreased susceptibility to most antimicrobial agents, which contributes to the persistence of infection. Drug resistance in fungal biofilms is multifactorial and phase-dependent; for example, efflux pumps mediate resistance in biofilms during early phase, whereas altered membrane sterol composition contributes to resistance in mature phase. Both substrate type and surface coatings play an important role in the pathogenesis of device-related fungal biofilms. Host immune cells influence the ability of Candida to form biofilms in vitro. This review summarizes recent advances in research on fungal biofilms and discusses their clinical relevance.     

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.     

Rhodotorula infection. A systematic review of 128 cases from literature

Rhodotorula is an emerging opportunistic pathogen, particularly in immunocompromised patients. Many cases of fungemia associated with catheters, endocarditis, peritonitis, meningitis, and endophthalmitis are infections incited by this yeast. The main purpose of this study was to review all cases of Rhodotorula infection reported in the literature and to describe risk factors, underlying conditions and outcome. From 128 cases, 79% were fungemia (103 cases), 7% eye infections (nine cases) and 5% (six cases) peritonitis associated with continuous ambulatory peritoneal dialysis. Eighty seven percent of Rhodotorula infections are associated with underlying immunosuppression or cancer. The most common isolated risk factor associated with Rhodotorula infection was the use of a central venous catheter, which was found in 83.4% of Rhodotorula fungemia (86 cases). Rhodotorula mucilaginosa was the most common species of fungemia (74% of cases), followed by Rhodotorula glutinis with 7.7%. The species was not identified in 17% of the cases of fungemias. Amphotericin was the drug of choice in the treatment of fungemia and most of the eye infections were treated with topical amphotericin, although all patients lost their vision. All peritonitis cases associated with continous ambulatory peritoneal dialysis needed to have the Tenckoff catheter changed. The overall mortality of Rhodotorula infection was 12.6%.     

Peritonitis during continuous ambulatory peritoneal dialysis in children.

The use of continuous ambulatory peritoneal dialysis (CAPD) in children has proved beneficial. However, peritonitis remains the major complication. A review of the incidence of peritonitis in 55 children (mean age 9.6 years) who underwent CAPD between 1978 and 1984 showed that there were 67 episodes of peritonitis (1 per 9.4 patient-months) in 33 of the 55. Three patients accounted for 22 of the episodes. In all cases, treatment with antibiotics, given intraperitoneally, was successful. Cephalothin was routinely given for infections due to gram-positive organisms, tobramycin for infections due to gram-negative organisms. Peritonitis recurred in seven patients, of whom five had to have their catheters replaced because of associated chronic infections of the deep peritoneal cuff, the exit site or the catheter tunnel. Although peritonitis was a common complication of CAPD in this population, it did not affect the success of the technique.     

Staphylococcal biofilms: structure, regulation, rejection

Staphylococci are able to cause chronic (persistent) infections, which develop in native tissues as well as on invasive materials artificially introduced into an organism. Such infections are associated with formation of biofilms. The review determines the definition of biofilms, describes factors, which contribute to their formation, characterizes adaptive stability of staphylococcal biofilms, which provides their long-term persistence in host organism. Genetic organization and regulation of polysaccharide and protein biofilms of staphylococci are described. Strategy for prevention and treatment of staphylococcal biofilm diseases is discussed.     

Peritoneal dialysis-related peritonitis due to Staphylococcus aureus: a single-center experience over 15 years

Peritonitis caused by Staphylococcus aureus is a serious complication of peritoneal dialysis (PD), which is associated with poor outcome and high PD failure rates. We reviewed the records of 62 S. aureus peritonitis episodes that occurred between 1996 and 2010 in the dialysis unit of a single university hospital and evaluated the host and bacterial factors influencing peritonitis outcome. Peritonitis incidence was calculated for three subsequent 5-year periods and compared using a Poisson regression model. The production of biofilm, enzymes, and toxins was evaluated. Oxacillin resistance was evaluated based on minimum inhibitory concentration and presence of the mecA gene. Logistic regression was used for the analysis of demographic, clinical, and microbiological factors influencing peritonitis outcome. Resolution and death rates were compared with 117 contemporary coagulase-negative staphylococcus (CoNS) episodes. The incidence of S. aureus peritonitis declined significantly over time from 0.13 in 1996–2000 to 0.04 episodes/patient/year in 2006–2010 (p = 0.03). The oxacillin resistance rate was 11.3%. Toxin and enzyme production was expressive, except for enterotoxin D. Biofilm production was positive in 88.7% of strains. The presence of the mecA gene was associated with a higher frequency of fever and abdominal pain. The logistic regression model showed that diabetes mellitus (p = 0.009) and β-hemolysin production (p = 0.006) were independent predictors of non-resolution of infection. The probability of resolution was higher among patients aged 41 to 60 years than among those >60 years (p = 0.02). A trend to higher death rate was observed for S. aureus episodes (9.7%) compared to CoNS episodes (2.5%), (p = 0.08), whereas resolution rates were similar. Despite the decline in incidence, S. aureus peritonitis remains a serious complication of PD that is associated with a high death rate. The outcome of this infection is negatively influenced by host factors such as age and diabetes mellitus. In addition, β-hemolysin production is predictive of non-resolution of infection, suggesting a pathogenic role of this factor in PD-related S. aureus peritonitis.     

白色念珠菌生物被膜研究进展

难治性真菌感染的临床分析发现,病灶感染病原常以生物被膜的形态存在。生物被膜的形成可帮助真菌躲避宿主细胞免疫系统清除和药物的攻击,所造成的持续性感染严重威胁人类健康,因此,认识研究真菌生物被膜及其耐药机理对于防治临床真菌感染有着重大意义。白色念珠菌是一种临床感染常见的条件性致病菌,也是目前真菌生物被膜研究的主要研究模型。白色念珠菌生物被膜主要由多糖、蛋白质和DNA构成,其形成由微生物间的群体感应调控,并受到环境中营养成分及其附着物表面性质影响。研究发现,胞外基质的屏障作用、耐药基因的表达等机制与生物被膜耐药性的产生密切相关。本文就白色念珠菌生物被膜的形成过程、结构组成、形成的影响因素、现有研究模型、耐药机制和治疗策略等几个方面介绍近年来的研究进展。     

Antifungal lock therapy: an eternal promise or an effective alternative therapeutic approach?

Each year, millions of central venous catheter insertions are performed in intensive care units worldwide. The usage of these indwelling devices is associated with a high risk of bacterial and fungal colonization, leading to the development of microbial consortia, namely biofilms. These sessile structures provide fungal cells with resistance to the majority of antifungals, environmental stress and host immune responses. Based on different guidelines, colonized/infected catheters should be removed and changed immediately in the case of Candida-related central line infections. However, catheter replacement is not feasible for all patient populations. An alternative therapeutic approach may be antifungal lock therapy, which has received high interest, especially in the last decade. This review summarizes the published Candida-related in vitro, in vivo data and case studies in terms of antifungal lock therapy. The number of clinical studies remains limited and further studies are needed for safe implementation of the antifungal lock therapy into clinical practice.     

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.     

Intracellular survival and innate immune evasion of Burkholderia cepacia: Improved understanding of quorum sensing-controlled virulence factors,biofilm, and inhibitors

Burkholderia cepacia complex (Bcc) are opportunistic pathogens implicated with nosocomial infections, and high rates of morbidity and mortality, especially in individuals with cystic fibrosis (CF). B. cepacia are naturally resistant to different classes of antibiotics, and can subvert the host innate immune responses by producing quorum sensing (QS) controlled virulence factors and biofilms. It still remains a conundrum as to how exactly the bacterium survives the intracellular environment within the host cells of CF patients and immunocompromised individuals although the bacterium can invade human lung epithelial cells, neutrophils, and murine macrophages. The mechanisms associated with intracellular survival in the airway epithelial cells and the role of QS and virulence factors in B. cepacia infections in cystic fibrosis remain largely unclear. The current review focuses on understanding the role of QS-controlled virulence factors and biofilms, and provides additional impetus to understanding the potentials of QS-inhibitory strategies against B. cepacia.     

A novel in vitro model for haematogenous spreading of S. aureus device biofilms demonstrating clumping dispersal as an advantageous dissemination mechanism

Staphylococcus aureus is able to disseminate from vascular device biofilms to the blood and organs, resulting in life‐threatening infections such as endocarditis. The mechanisms behind spreading are largely unknown, especially how the bacterium escapes immune effectors and antibiotics in the process. Using an in vitro catheter infection model, we studied S. aureus biofilm growth, late‐stage dispersal, and reattachment to downstream endothelial cell layers. The ability of the released biofilm material to resist host response and disseminate in vivo was furthermore studied in whole blood and phagocyte survival assays and in a short‐term murine infection model. We found that S. aureus biofilms formed in flow of human plasma release biofilm thromboemboli with embedded bacteria and bacteria‐secreted polysaccharides. The emboli disseminate as antibiotic and immune resistant vehicles that hold the ability to adhere to and initiate colonisation of endothelial cell layers under flow. In vivo experiments showed that the released biofilm material reached the heart similarly as ordinary broth‐grown bacteria but also that clumps to some extend were trapped in the lungs. The clumping dispersal of S. aureus from in vivo‐like vascular biofilms and their specific properties demonstrated here help explain the pathophysiology associated with S. aureus bloodstream infections.     

Staphylococcus aureus biofilms prevent macrophage phagocytosis and attenuate inflammation in vivo

Biofilms are complex communities of bacteria encased in a matrix composed primarily of polysaccharides, extracellular DNA, and protein. Staphylococcus aureus can form biofilm infections, which are often debilitating due to their chronicity and recalcitrance to antibiotic therapy. Currently, the immune mechanisms elicited during biofilm growth and their impact on bacterial clearance remain to be defined. We used a mouse model of catheter-associated biofilm infection to assess the functional importance of TLR2 and TLR9 in the host immune response during biofilm formation, because ligands for both receptors are present within the biofilm. Interestingly, neither TLR2 nor TLR9 impacted bacterial density or inflammatory mediator secretion during biofilm growth in vivo, suggesting that S. aureus biofilms circumvent these traditional bacterial recognition pathways. Several potential mechanisms were identified to account for biofilm evasion of innate immunity, including significant reductions in IL-1β, TNF-α, CXCL2, and CCL2 expression during biofilm infection compared with the wound healing response elicited by sterile catheters, limited macrophage invasion into biofilms in vivo, and a skewing of the immune response away from a microbicidal phenotype as evidenced by decreases in inducible NO synthase expression concomitant with robust arginase-1 induction. Coculture studies of macrophages with S. aureus biofilms in vitro revealed that macrophages successful at biofilm invasion displayed limited phagocytosis and gene expression patterns reminiscent of alternatively activated M2 macrophages. Collectively, these findings demonstrate that S. aureus biofilms are capable of attenuating traditional host proinflammatory responses, which may explain why biofilm infections persist in an immunocompetent host.     

Review of techniques for diagnosis of catheter-related Candida biofilm infections

Recent evidence shows that many hospital-acquired infections, including most device-associated infections, involve the persistence of sessile organisms in the form of biofilms that are attached to a device surface and encased in an extracellular matrix. The cells in this environment exhibit an altered phenotype with respect to antimicrobial resistance and thus are extraordinarily difficult to eradicate without device removal. Although a number of implantable and topical devices are at risk for Candida biofilm formation, this review focuses on the diagnosis of the most common of these infections, biofilm growth on the surface of central venous catheters and urinary catheters.     

Seeking clarity within cloudy effluents: differentiating fungal from bacterial peritonitis in peritoneal dialysis patients

Background

Fungal peritonitis is a serious complication of peritoneal dialysis (PD) therapy with the majority of patients ceasing PD permanently. The aims of this study were to identify risk factors and clinical associations that may discriminate between fungal from bacterial peritonitis.

Methods

We retrospectively identified episodes of fungal peritonitis from 2001–2010 in PD patients at Liverpool and Westmead Hospitals (Australia). Fungal peritonitis cases were matched in a 1∶2 ratio with patients with bacterial peritonitis from each institution''s dialysis registry, occurring closest in time to the fungal episode. Patient demographic, clinical and outcome data were obtained from the medical records.

Results

Thirty-nine episodes of fungal peritonitis (rate of 0.02 episodes per patient-year of dialysis) were matched with 78 episodes of bacterial peritonitis. Candida species were the commonest pathogens (35/39; 90% episodes) with Candida albicans (37%), Candida parapsilosis (32%) and Candida glabrata (13%) the most frequently isolated species. Compared to bacterial peritonitis, fungal peritonitis patients had received PD for significantly longer (1133 vs. 775 catheter-days; p = 0.016), were more likely to have had previous episodes of bacterial peritonitis (51% vs. 10%; p = 0.01), and to have received prior antibacterial therapy (51% vs. 10%; p = 0.01). Patients with fungal peritonitis were less likely to have fever and abdominal pain on presentation, but had higher rates of PD catheter removal (79% vs. 22%; p<0.005), and permanent transfer to haemodialysis (87% vs. 24%; p<0.005). Hospital length of stay was significantly longer in patients with fungal peritonitis (26.1 days vs. 12.6 days; p = 0.017), but the all-cause 30-day mortality rate was similar in both groups. Fluconazole was a suitable empiric antifungal agent; with no Candida resistance detected.

Conclusion

Prompt recognition of clinical risk factors, initiation of antifungal therapy and removal of PD catheters are key considerations in optimising outcomes.     

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.     

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.     

Preclinical Assessment of Adjunctive tPA and DNase for Peritoneal Dialysis Associated Peritonitis

A major complication of peritoneal dialysis is the development of peritonitis, which is associated with reduced technique and patient survival. The inflammatory response elicited by infection results in a fibrin and debris-rich environment within the peritoneal cavity, which may reduce the effectiveness of antimicrobial agents and predispose to recurrence or relapse of infection. Strategies to enhance responses to antimicrobial agents therefore have the potential to improve patient outcomes. This study presents pre-clinical data describing the compatibility of tPA and DNase in combination with antimicrobial agents used for the treatment of PD peritonitis. tPA and DNase were stable in standard dialysate solution and in the presence of antimicrobial agents, and were safe when given intraperitoneally in a mouse model with no evidence of local or systemic toxicity. Adjunctive tPA and DNase may have a role in the management of patients presenting with PD peritonitis.