Evaluation of Caspofungin and Amphotericin B Deoxycholate againstCandida albicansBiofilms in an Experimental Intravascular Catheter Infection Model

Combination of Systemic and Lock-Therapies with Micafungin Eradicate Catheter-Based Biofilms and Infections Caused by Candida albicans and Candida parapsilosis in Neutropenic Rabbit Models

Vascular catheter-related infections, primarily caused by Candida albicans and Candida parapsilosis, pose significant challenges due to the formation of biofilms on catheters, leading to refractory disease and considerable morbidity. We studied the efficacy of micafungin in systemic and lock therapies to eliminate catheter-based biofilms and deep tissue infections in experimental central venous catheter (CVC)-related candidemia in neutropenic rabbits. Silastic CVCs in rabbits were inoculated with 1 × 103 CFU/mL of C. albicans or C. parapsilosis, establishing catheter-based biofilm, and subjected to various treatments. Neutropenic rabbits treated with a combination of lock therapy and systemic micafungin demonstrated the most significant reduction in fungal burden, from 5.0 × 104 to 1.8 × 102 CFU/mL of C. albicans and from 5.9 × 104 to 2.7 × 102 CFU/mL of C. parapsilosis (p ≤ 0.001), in the CVC after 24 h, with full clearance of blood cultures after 72 h from treatment initiation. The combination of lock and systemic micafungin therapy achieved eradication of C. albicans from all studied tissues (0.0 ± 0.0 log CFU/g) vs. untreated controls (liver 7.5 ± 0.22, spleen 8.3 ± 0.25, kidney 8.6 ± 0.07, cerebrum 6.3 ± 0.31, vena cava 6.6 ± 0.29, and CVC wash 2.3 ± 0.68 log CFU/g) (p ≤ 0.001). Rabbits treated with a combination of lock and systemic micafungin therapy demonstrated a ≥2 log reduction in C. parapsilosis in all treated tissues (p ≤ 0.05) except kidney. Serum (1→3)-β-D-glucan levels demonstrated significant decreases in response to treatment. The study demonstrates that combining systemic and lock therapies with micafungin effectively eradicates catheter-based biofilms and infections caused by C. albicans or C. parapsilosis, particularly in persistently neutropenic conditions, offering promising implications for managing vascular catheter-related candidemia and providing clinical benefits in cases where catheter removal is not feasible.

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.

Association of different Candida species with catheter-related candidemia, and the potential antifungal treatments against their adhesion properties and biofilm-forming capabilities

Background

To compare the adhesion properties and biofilm‐forming capabilities of 27 Candida isolates obtained from catheter‐related candidemia patients and to evaluate the inhibitory effects of antifungal agents on different Candida species.

Material and Methods

Seven C. albicans, six C. parapsilosis, five C. guilliermondii, five C. tropicalis, and four C. glabrata clinical isolates were investigated. We quantified the adherence of these Candida species by flow cytometric method and evaluated the formation of biofilms by XTT reduction and crystal violet methods. Actions of micafungin (MF), fluconazole (FZ), and N‐acetylcysteine (NAC) on the adhesion and biofilm formation of different Candida species were determined.

Results

Non‐albicans Candida species were demonstrated to have stronger adhesion abilities compared with C. albicans. The biofilm‐forming capabilities of different Candida species were varied considerably, and the degree of biofilm formation might be affected by different assay approaches. Interestingly, C. parapsilosis displayed the highest biofilm formation abilities, while C. glabrata exhibited the lowest total biomass and metabolic activity. Furthermore, the inhibitory activities of MF, FZ, and NAC on fungal adhesion and biofilm formation were evaluated, and the results indicated that MF could reduce the adhesion ability and biofilm metabolism more significantly (p < 0.05), and its antifungal activity was elevated in a dose‐dependent manner.

Conclusion

Non‐albicans Candida species, especially C. guilliermondii, C. tropicalis, and C. parapsilosis, exhibited higher adhesion ability in catheter‐related candidemia patients. However, these Candida species had varied biofilm‐forming capabilities. MF tended to have stronger inhibitory effects against both adhesion and biofilm formation of different Candida species.

Candida albicans biofilms and polymicrobial interactions

Candida albicans is a common fungus of the human microbiota. While generally a harmless commensal in healthy individuals, several factors can lead to its overgrowth and cause a range of complications within the host, from localized superficial infections to systemic life-threatening disseminated candidiasis. A major virulence factor of C. albicans is its ability to form biofilms, a closely packed community of cells that can grow on both abiotic and biotic substrates, including implanted medical devices and mucosal surfaces. These biofilms are extremely hard to eradicate, are resistant to conventional antifungal treatment and are associated with high morbidity and mortality rates, making biofilm-associated infections a major clinical challenge. Here, we review the current knowledge of the processes involved in C. albicans biofilm formation and development, including the central processes of adhesion, extracellular matrix production and the transcriptional network that regulates biofilm development. We also consider the advantages of the biofilm lifestyle and explore polymicrobial interactions within multispecies biofilms that are formed by C. albicans and selected microbial species.

Efficacy of liposomal amphotericin B and anidulafungin using an antifungal lock technique (ALT) for catheter-related Candida albicans and Candida glabrata infections in an experimental model

Objective

The aims of this study were as follows. First, we sought to compare the in vitro susceptibility of liposomal amphotericin B (LAmB) and anidulafungin on Candida albicans and Candida glabrata biofilms growing on silicone discs. Second, we sought to compare the activity of LAmB versus anidulafungin for the treatment of experimental catheter-related C. albicans and C. glabrata infections with the antifungal lock technique in a rabbit model.

Methods

Two C. albicans and two C. glabrata clinical strains were used. The minimum biofilm eradication concentration for 90% eradication (MBEC₉₀) values were determined after 48h of treatment with LAmB and anidulafungin. Confocal microscopy was used to visualize the morphology and viability of yeasts growing in biofilms. Central venous catheters were inserted into New Zealand rabbits, which were inoculated of each strain of C. albicans and C. glabrata. Then, catheters were treated for 48h with saline or with antifungal lock technique using either LAmB (5mg/mL) or anidulafungin (3.33mg/mL).

Results

In vitro: anidulafungin showed greater activity than LAmB against C. albicans and C. glabrata strains. For C. albicans: MBEC₉₀ of anidulafungin versus LAmB: CA176, 0.03 vs. 128 mg/L; CA180, 0.5 vs. 64 mg/L. For C. glabrata: MBEC₉₀ of anidulafungin versus LAmB: CG171, 0.5 vs. 64 mg/L; CG334, 2 vs. 32 mg/L. In vivo: for C. albicans species, LAmB and anidulafungin achieved significant reductions relative to growth control of log₁₀ cfu recovered from the catheter tips (CA176: 3.6±0.3 log₁₀ CFU, p≤0.0001; CA180: 3.8±0.1 log₁₀ CFU, p≤0.01). For C. glabrata, anidulafungin lock therapy achieved significant reductions relative to the other treatments (CG171: 4.8 log₁₀ CFU, p≤0.0001; CG334: 5.1 log₁₀ CFU, p≤0.0001)

Conclusions

For the C. albicans strains, both LAmB and anidulafungin may be promising antifungal lock technique for long-term catheter-related infections; however, anidulafungin showed significantly higher activity than LAmB against the C. glabrata strains.

Adhesins of Yeasts: Protein Structure and Interactions

The ability of yeast cells to adhere to other cells or substrates is crucial for many yeasts. The budding yeast Saccharomyces cerevisiae can switch from a unicellular lifestyle to a multicellular one. A crucial step in multicellular lifestyle adaptation is self-recognition, self-interaction, and adhesion to abiotic surfaces. Infectious yeast diseases such as candidiasis are initiated by the adhesion of the yeast cells to host cells. Adhesion is accomplished by adhesin proteins that are attached to the cell wall and stick out to interact with other cells or substrates. Protein structures give detailed insights into the molecular mechanism of adhesin-ligand interaction. Currently, only the structures of a very limited number of N-terminal adhesion domains of adhesins have been solved. Therefore, this review focuses on these adhesin protein families. The protein architectures, protein structures, and ligand interactions of the flocculation protein family of S. cerevisiae; the epithelial adhesion family of C. glabrata; and the agglutinin-like sequence protein family of C. albicans are reviewed and discussed.

Effect of peritoneal dialysis fluids on activity of echinocandins against Candida spp. biofilm

Peritoneal dialysis fluids (PDFs) impair microorganisms' growth, which may compromise effectivity of some antimicrobials. The purpose of this study was to investigate the effect of three different PDFs (lactate/bicarbonate-buffered Physioneal 40® with 2.2% glucose, lactate-buffered Nutrineal PD4® with 1.1% amino acid, and lactate-buffered Extraneal® with 7.5% icodextrin) on biofilm formation of four different Candida spp and antibiofilm effectiveness of anidulafungin, caspofungin and micafungin against Candida spp. biofilm in PDFs. All tested PDFs attained inhibitory effect on the biofilm formation but also reduced biofilm effectiveness of echinocandins against biofilm in PDFs was detected.

Microbial Biofilms in Pulmonary and Critical Care Diseases

Microbial biofilms can colonize medical devices and human tissues, and their role in microbial pathogenesis is now well established. Not only are biofilms ubiquitous in natural and human-made environments, but they are also estimated to be associated with approximately two-thirds of nosocomial infections. This multicellular aggregated form of microbial growth confers a remarkable resistance to killing by antimicrobials and host defenses, leading biofilms to cause a wide range of subacute or chronic infections that are difficult to eradicate. We have gained tremendous knowledge on the molecular, genetic, microbiological, and biophysical processes involved in biofilm formation. These insights now shape our understanding, diagnosis, and management of many infectious diseases and direct the development of novel antimicrobial therapies that target biofilms. Bacterial and fungal biofilms play an important role in a range of diseases in pulmonary and critical care medicine, most importantly catheter-associated infections, ventilator-associated pneumonia, chronic Pseudomonas aeruginosa infections in cystic fibrosis lung disease, and Aspergillus fumigatus pulmonary infections.

What Could Be the Role of Antifungal Lock-Solutions? From Bench to Bedside

Candidemia related to the presence of a biofilm are often reported in patients with vascular catheters. Once they are mature, biofilms are persistent infectious reservoirs, and the yeasts dispersed from biofilms can cause infections. Sessile yeasts typically display increased levels of resistance to most antimicrobial agents and systemic treatments usually fail to eradicate previously formed fungal biofilms. In a curative strategy, antifungal lock therapy may help to sterilize catheters, with very high concentrations of antifungal agents, which are not compatible with systemic use. This strategy has been studied by several authors in in vitro and in vivo studies, and more rarely, in clinical settings for adult and paediatric patients. Our study aims to assess the efficacy of the antifungal solutions used for lock therapy and demonstrated by the different teams.

Photodynamic Antimicrobial Chemotherapy (PACT), using Toluidine blue O inhibits the viability of biofilm produced by Candida albicans at different stages of development

BACKGROUND

Candida albicans is an opportunistic fungus producing both superficial and systemic infections, especially in immunocompromised individuals. It has been demonstrated that C. albicans ability to form biofilms is a crucial process for colonization and virulence. Furthermore, a correlation between the development of drug resistance and biofilm maturation at Candida biofilms has been shown. Photodynamic Antimicrobial Chemotherapy (PACT) is a potential antimicrobial therapy that combines visible light and a non-toxic dye, known as a photosensitizer, producing reactive oxygen species (ROS) that can kill the treated cells. The objective of this study was to investigate the effects of PACT, using Toluidine Blue O (TBO) on the viability of biofilms produced by C. albicans at different stages of development.

METHODS

In this study, the effects of PACT on both biofilm formation and viability of the biofilm produced by C. albicans were studied. Biofilm formation and viability were determined by a metabolic assay based on the reduction of XTT assay. In addition, the morphology of the biofilm was observed using light microscopy.

RESULTS

PACT inhibited both biofilm formation and viability of the biofilm produced by C. albicans. Furthermore, PACT was able to decrease the number of both cells and filamentous form present in the biofilm structure. This inhibitory effect was observed in both early and mature biofilms.

CONCLUSIONS

The results obtained in this study demonstrated the potential of PACT (using TBO) as an effective antifungal therapy, including against infections associated with biofilms at different stages of development.

Development and regulation of single- and multi-species Candida albicans biofilms

Candida albicans is among the most prevalent fungal species of the human microbiota and asymptomatically colonizes healthy individuals. However, it is also an opportunistic pathogen that can cause severe, and often fatal, bloodstream infections. The medical impact of C. albicans typically depends on its ability to form biofilms, which are closely packed communities of cells that attach to surfaces, such as tissues and implanted medical devices. In this Review, we provide an overview of the processes involved in the formation of C. albicans biofilms and discuss the core transcriptional network that regulates biofilm development. We also consider some of the advantages that biofilms provide to C. albicans in comparison with planktonic growth and explore polymicrobial biofilms that are formed by C. albicans and certain bacterial species.

Time-Lapse Tracking of Candida tropicalis Biofilm Formation and the Antifungal Efficacy of Liposomal Amphotericin B

Candida species bloodstream infection, or candidemia, remains an important health issue with high morbidity and mortality. Bloodstream infections caused by Candida species are often associated with the ability of Candida to form biofilms on medical devices, such as central venous catheters. Non-albicans Candida species have been increasing gradually in clinical settings. Another Candida species, C. tropicalis, has a propensity to form biofilms and is also an independent risk factor for high morbidity and mortality in hospitalized patients. This study was conducted to investigate the process of biofilm formation by C. tropicalis and the antifungal activity of liposomal amphotericin B (LAB) against both forming biofilms and developed biofilms using time-lapse imaging. We found that C. tropicalis has a high capacity for hyphal growth and gas generation due to its high metabolic activity. Thus, we visually observed the formation of aggressive C. tropicalis biofilms, which are fast-growing biofilms. We found that LAB acts immediately and completely inhibits forming biofilms. Furthermore, we demonstrated that LAB was effective against developed C. tropicalis biofilms by reducing the growth of hyphae and morphological changes. These results suggest that LAB may be effective for the treatment of infections caused by catheter-related C. tropicalis biofilms.

ECIL-6 guidelines for the treatment of invasive candidiasis, aspergillosis and mucormycosis in leukemia and hematopoietic stem cell transplant patients

The European Conference on Infections in Leukemia (ECIL) provides recommendations for diagnostic strategies and prophylactic, pre-emptive or targeted therapy strategies for various types of infection in patients with hematologic malignancies or hematopoietic stem cell transplantation recipients. Meetings are held every two years since 2005 and evidence-based recommendations are elaborated after evaluation of the literature and discussion among specialists of nearly all European countries. In this manuscript, the ECIL group presents the 2015-update of the recommendations for the targeted treatment of invasive candidiasis, aspergillosis and mucormycosis. Current data now allow a very strong recommendation in favor of echinocandins for first-line therapy of candidemia irrespective of the underlying predisposing factors. Anidulafungin has been given the same grading as the other echinocandins for hemato-oncological patients. The beneficial role of catheter removal in candidemia is strengthened. Aspergillus guidelines now recommend the use of either voriconazole or isavuconazole for first-line treatment of invasive aspergillosis, while first-line combination antifungal therapy is not routinely recommended. As only few new data were published since the last ECIL guidelines, no major changes were made to mucormycosis recommendations.

Future therapies targeted towards eliminating Candida biofilms and associated infections

INTRODUCTION

Candida species are common human commensals and cause either superficial or invasive opportunistic infections. The biofilm form of candida as opposed to its suspended, planktonic form, is predominantly associated with these infections. Alternative or adjunctive therapies are urgently needed to manage Candida infections as the currently available short arsenal of antifungal drugs has been compromised due to their systemic toxicity, cross-reactivity with other drugs, and above all, by the emergence of drug-resistant Candida species due to irrational drug use. Areas covered: Combination anti-Candida therapies, antifungal lock therapy, denture cleansers, and mouth rinses have all been proposed as alternatives for disrupting candidal biofilms on different substrates. Other suggested approaches for the management of candidiasis include the use of natural compounds, such as probiotics, plants extracts and oils, antifungal quorum sensing molecules, anti-Candida antibodies and vaccines, cytokine therapy, transfer of primed immune cells, photodynamic therapy, and nanoparticles. Expert commentary: The sparsity of currently available antifungals and the plethora of proposed anti-candidal therapies is a distinct indication of the urgent necessity to develop efficacious therapies for candidal infections. Alternative drug delivery approaches, such as probiotics, reviewed here is likely to be a reality in clinical settings in the not too distant future.

Pathogenesis of Candida albicans biofilm

Candida albicans is the most common human fungal pathogen causing diseases ranging from mucosal to systemic infections. As a commensal, C. albicans asymptomatically colonizes mucosal surfaces; however, any disruption in the host environment or under conditions of immune dysfunction, C. albicans can proliferate and invade virtually any site in the host. The ability of this highly adaptable fungal species to transition from commensal to pathogen is due to a repertoire of virulence factors. Specifically, the ability to switch morphology and form biofilms are properties central to C. albicans pathogenesis. In fact, the majority of C. albicans infections are associated with biofilm formation on host or abiotic surfaces such as indwelling medical devices, which carry high morbidity and mortality. Significantly, biofilms formed by C. albicans are inherently tolerant to antimicrobial therapy and therefore, the susceptibility of Candida biofilms to the current therapeutic agents remains low. The aim of this review is to provide an overview of C. albicans highlighting some of the diverse biofilm-associated diseases caused by this opportunistic pathogen and the animal models available to study them. Further, the classes of antifungal agents used to combat these resilient infections are discussed along with mechanisms of drug resistance.

The Role of Echinocandins in Candida Biofilm-Related Vascular Catheter Infections: In Vitro and In Vivo Model Systems

Candida biofilm-associated infections of central venous catheters are a challenging therapeutic problem. Recent in vitro and in vivo studies of the structure, formation, pathogenesis, and treatment establish a rationale for new approaches to management of these tenacious infections.

Role of Echinocandins in Fungal Biofilm-Related Disease: Vascular Catheter-Related Infections, Immunomodulation, and Mucosal Surfaces

Biofilm-related infections have become an increasingly important clinical problem. Many of these infections occur in patients with multiple comorbidities or with impaired immunity. Echinocandins (caspofungin, micafungin, and anidulafungin) exert their fungicidal activity by inhibition of the synthesis of the (1→3)-β-d-glucan. They are active among in vitro and in vivo model systems against a number of Candida species and filamentous fungi in their planktonic and biofilm phenotype. Their superior activity against biofilms poses them in an advantageous position among the antifungal armamentarium. However, additional studies are warranted to expand our knowledge on the role of echinocandins against biofilm-related infections.

The clinical importance of fungal biofilms

Fungal biofilms have become an increasingly important clinical problem. The widespread use of antibiotics, frequent use of indwelling medical devices, and a trend toward increased patient immunosuppression have resulted in a creation of opportunity for clinically important yeasts and molds to form biofilms. This review will discuss the diversity and importance of fungal biofilms in the context of clinical medicine, provide novel insights into the clinical management of fungal biofilm infection, present evidence why these structures are recalcitrant to antifungal therapy, and discuss how our knowledge and understanding may lead to novel therapeutic intervention.

From Biology to Drug Development: New Approaches to Combat the Threat of Fungal Biofilms

Fungal infections constitute a major threat to an escalating number of critically ill patients. Fungi are eukaryotic organisms and, as such, there is a limited armamentarium of antifungal drugs, which leads to high mortality rates. Moreover, fungal infections are often associated with the formation of biofilms, which contribute to virulence and further complicate treatment due to the high level of antifungal drug resistance displayed by sessile cells within these microbial communities. Thus, the treatment of fungal infections associated with a biofilm etiology represents a formidable and unmet clinical challenge. The increasing importance and awareness of fungal biofilms is reflected by the fact that this is now an area of very active research. Studies in the last decade have provided important insights into fungal biofilm biology, physiology, and pathology, as well as into the molecular basis of biofilm resistance. Here we discuss how this accumulated knowledge may inform the development of new antibiofilm strategies and therapeutics that are urgently needed.

Fungal Biofilms: In Vivo Models for Discovery of Anti-Biofilm Drugs

During infection, fungi frequently transition to a biofilm lifestyle, proliferating as communities of surface-adherent aggregates of cells. Phenotypically, cells in a biofilm are distinct from free-floating cells. Their high tolerance of antifungals and ability to withstand host defenses are two characteristics that foster resilience. Biofilm infections are particularly difficult to eradicate, and most available antifungals have minimal activity. Therefore, the discovery of novel compounds and innovative strategies to treat fungal biofilms is of great interest. Although many fungi have been observed to form biofilms, the most well-studied is Candida albicans. Animal models have been developed to simulate common Candida device-associated infections, including those involving vascular catheters, dentures, urinary catheters, and subcutaneous implants. Models have also reproduced the most common mucosal biofilm infections: oropharyngeal and vaginal candidiasis. These models incorporate the anatomical site, immune components, and fluid dynamics of clinical niches and have been instrumental in the study of drug resistance and investigation of novel therapies. This chapter describes the significance of fungal biofilm infections, the animal models developed for biofilm study, and how these models have contributed to the development of new strategies for the eradication of fungal biofilm infections.

In vitro efficacy of liposomal amphotericin B, micafungin and fluconazole against non-albicans Candida species biofilms

Non-albicans Candida species are being isolated with increasing frequency. In this study, biofilm formation by Candida tropicalis, Candida parapsilosis and Candida glabrata was evaluated and the activities of liposomal amphotericin B (LAB), micafungin (MFG) and fluconazole (FLC) against these biofilms were assessed using a clinically relevant in vitro model system. LAB exhibited strong activities against the three non-albicans Candida species and showed dose-dependent efficacy. MFG displayed a paradoxical growth effect against the C. tropicalis biofilm. FLC was ineffective for non-albicans biofilms. This study shows that Candida biofilms have unique susceptibility to LAB. The dose-dependent effects of LAB indicate that this drug may be a useful treatment for biofilm formation by non-albicans Candida species in cases in which the catheter cannot be removed for clinical reasons.

Antibiofilm Activity of Low-Amperage Continuous and Intermittent Direct Electrical Current

Bacterial biofilms are difficult to treat using available antimicrobial agents, so new antibiofilm strategies are needed. We previously showed that 20, 200, and 2,000 μA of electrical current reduced bacterial biofilms of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. Here, we tested continuous direct current at lower amperages, intermittent direct current, and combinations of surface materials (Teflon or titanium) and electrode compositions (stainless steel, graphite, titanium, or platinum) against S. aureus, S. epidermidis, and P. aeruginosa biofilms. In addition, we tested 200 or 2,000 μA for 1 and 4 days against biofilms of 33 strains representing 13 species of microorganisms. The logarithmic reduction factor was used to measure treatment effects. Using continuous current delivery, the lowest active amperage was 2 μA for 1, 4, or 7 days against P. aeruginosa and 5 μA for 7 days against S. epidermidis and S. aureus biofilms. Delivery of 200 μA for 4 h a day over 4 days reduced P. aeruginosa, S. aureus, and S. epidermidis biofilms on Teflon or titanium discs. A reduction of P. aeruginosa, S. aureus, and S. epidermidis biofilms was measured for 23 of 24 combinations of surface materials and electrode compositions tested. Four days of direct current delivery reduced biofilms of 25 of 33 strains studied. In conclusion, low-amperage current or 4 h a day of intermittent current delivered using a variety of electrode compositions reduced P. aeruginosa, S. aureus, and S. epidermidis biofilms on a variety of surface materials. The electricidal effect was observed against a majority of bacterial species studied.

The Role of Antifungals against Candida Biofilm in Catheter-Related Candidemia

Catheter-related bloodstream infection (C-RBSI) is one of the most frequent nosocomial infections. It is associated with high rates of morbidity and mortality. Candida spp. is the third most common cause of C-RBSI after coagulase-negative staphylococci and Staphylococcus aureus and is responsible for approximately 8% of episodes. The main cause of catheter-related candidemia is the ability of some Candida strains-mainly C. albicans and C. parapsilosis-to produce biofilms. Many in vitro and in vivo models have been designed to assess the activity of antifungal drugs against Candida biofilms. Echinocandins have proven to be the most active antifungal drugs. Potential options in situations where the catheter cannot be removed include the combination of systemic and lock antifungal therapy. However, well-designed and -executed clinical trials must be performed before firm recommendations can be issued.

Successful treatment of Candida osteoarticular infections with limited duration of antifungal therapy and orthopedic surgical intervention

BACKGROUND

Current guidelines for treatment of Candida osteoarticular infections (COAIs) recommend a prolonged course of antifungal therapy (AFT) of 6-12 months. Based upon strategies developed at the Hospital for Special Surgery (HSS), we hypothesized that the duration of antifungal therapy may be substantially reduced for management of COAI.

METHODS

This was a retrospective chart review of cases of COAI treated at the HSS for the past 14 years. COAI was documented by open biopsy and direct culture in all cases. The mean (95% confidence interval, CI) duration of documented follow-up was 39 (16-61) months.

RESULTS

Among the 23 cases of COAI, the median age was 62 years (range 22-83 years) with 61% having no underlying condition. Orthopedic appliances, including joint prostheses and fracture hardware, were present in 74% of cases. All patients had COAI as the first proven site of candidiasis. Candida albicans and Candida parapsilosis were the most common species. Hip, knee, foot, and ankle were the most common sites. All patients received aggressive surgical intervention followed by AFT administered for a mean (95% CI) duration of 45 (38-83) days. Systemic AFT consisted principally of fluconazole alone (65%) or in combination with other agents (26%). Adjunctive intraoperative amphotericin B irrigation was used in 35%. Among eight cases of CAOI that required placement of a new prosthetic joint, all were successfully treated. There were no microbiologic failures.

CONCLUSIONS

Candida osteoarticular infections may be successfully treated with substantially limited durations of AFT when combined with a thorough surgical approach.

Future directions for anti-biofilm therapeutics targeting Candida

While proliferating in its most common mode of growth, a biofilm, Candida spp. exhibit increased resistance to available antifungal agents. These adherent communities are difficult to eradicate and often responsible for treatment failures. New therapies are urgently needed to treat a variety of Candida biofilm infections in the medical setting. This review discusses the medical relevance of Candida biofilms, the drug resistance associated with this mode of growth, and approaches to combat these resilient infections.

Reactive oxygen species-inducing antifungal agents and their activity against fungal biofilms

Invasive fungal infections are associated with very high mortality rates ranging from 20–90% for opportunistic fungal pathogens such as Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus. Fungal resistance to antimycotic treatment can be genotypic (due to resistant strains) as well as phenotypic (due to more resistant fungal lifestyles, such as biofilms). With regard to the latter, biofilms are considered to be critical in the development of invasive fungal infections. However, there are only very few antimycotics, such as miconazole (azoles), echinocandins and liposomal formulations of amphotericin B (polyenes), which are also effective against fungal biofilms. Interestingly, these antimycotics all induce reactive oxygen species (ROS) in fungal (biofilm) cells. This review provides an overview of the different classes of antimycotics and novel antifungal compounds that induce ROS in fungal planktonic and biofilm cells. Moreover, different strategies to further enhance the antibiofilm activity of such ROS-inducing antimycotics will be discussed.

Antifungal therapy with an emphasis on biofilms

Fungal infections are on the rise as advances in modern medicine prolong the lives of severely ill patients. Fungi are eukaryotic organisms and there are a limited number of targets for antifungal drug development; as a result the antifungal arsenal is exceedingly limited. Azoles, polyenes and echinocandins constitute the mainstay of antifungal therapy for patients with life-threatening mycoses. One of the main factors complicating antifungal therapy is the formation of fungal biofilms, microbial communities displaying resistance to most antifungal agents. A better understanding of fungal biofilms provides for new opportunities for the development of urgently needed novel antifungal agents and strategies.

Potentiation of antibiofilm activity of amphotericin B by superoxide dismutase inhibition

This study demonstrates a role for superoxide dismutases (Sods) in governing tolerance of Candida albicans biofilms to amphotericin B (AmB). Coincubation of C. albicans biofilms with AmB and the Sod inhibitors N,N'-diethyldithiocarbamate (DDC) or ammonium tetrathiomolybdate (ATM) resulted in reduced viable biofilm cells and increased intracellular reactive oxygen species levels as compared to incubation of biofilm cells with AmB, DDC, or ATM alone. Hence, Sod inhibitors can be used to potentiate the activity of AmB against C. albicans biofilms.

Activities of systemically administered echinocandins against in vivo mature Candida albicans biofilms developed in a rat subcutaneous model

This study addresses the effects of micafungin, caspofungin, and anidulafungin against Candida albicans biofilms developed in a subcutaneous catheter rat model system. Doses of 5, 10, and 30 mg/kg (of body weight)/day (the last only for micafungin) were given intravenously for 5, 7, and 10 days. All three echinocandins caused a significant reduction of the Candida cell numbers on the implanted catheters and are thus promising for the treatment of biofilm-related infections.

Antifungal lock therapy

The widespread use of intravascular devices, such as central venous and hemodialysis catheters, in the past 2 decades has paralleled the increasing incidence of catheter-related bloodstream infections (CR-BSIs). Candida albicans is the fourth leading cause of hospital-associated BSIs. The propensity of C. albicans to form biofilms on these catheters has made these infections difficult to treat due to multiple factors, including increased resistance to antifungal agents. Thus, curing CR-BSIs caused by Candida species usually requires catheter removal in addition to systemic antifungal therapy. Alternatively, antimicrobial lock therapy has received significant interest and shown promise as a strategy to treat CR-BSIs due to Candida species. The existing in vitro, animal, and patient data for treatment of Candida-related CR-BSIs are reviewed. The most promising antifungal lock therapy (AfLT) strategies include use of amphotericin, ethanol, or echinocandins. Clinical trials are needed to further define the safety and efficacy of AfLT.

Antifungal lock therapy

The widespread use of intravascular devices, such as central venous and hemodialysis catheters, in the past 2 decades has paralleled the increasing incidence of catheter-related bloodstream infections (CR-BSIs). Candida albicans is the fourth leading cause of hospital-associated BSIs. The propensity of C. albicans to form biofilms on these catheters has made these infections difficult to treat due to multiple factors, including increased resistance to antifungal agents. Thus, curing CR-BSIs caused by Candida species usually requires catheter removal in addition to systemic antifungal therapy. Alternatively, antimicrobial lock therapy has received significant interest and shown promise as a strategy to treat CR-BSIs due to Candida species. The existing in vitro, animal, and patient data for treatment of Candida-related CR-BSIs are reviewed. The most promising antifungal lock therapy (AfLT) strategies include use of amphotericin, ethanol, or echinocandins. Clinical trials are needed to further define the safety and efficacy of AfLT.

Echinocandins: are they all the same?

The discovery of echinocandins, and their development and approval, was hailed as a significant addition to our antifungal armamentarium, previously predominated by polyenes and azoles. To date, three echinocandins (anidulafungin, caspofungin, and micafungin) have been approved by the U.S. Food and Drug Administration for the treatment of fungal infections. Since all three echinocandins target the fungal cell wall and share a similar structural chemical backbone, they are perceived to be identical. However, a scientific literature review shows distinct differences among the echinocandins in terms of in vitro activity, fungicidal activity, post-antifungal effect, paradoxical effect, and activity on biofilms. More investigation is warranted to determine if the observed differences among the echinocandins can translate to clinical advantages.

Effect of Amphotericin B Alone or in Combination with Rifampicin or Clarithromycin Against Candida Species Biofilms

Effectiveness of amphotericin B alone or in combination with rifampicin or clarithromycin on the killing of Candida species biofilms was investigated in vitro. Amphotericin B was assayed at 0.005 to 10 mg/ml. Rifampin and clarithromycin were assayed at 10 mg/ml. We studied 7 Candida albicans, 3 Candida parapsilosis, 3 Candida glabrata, 3 Candida krusei and 2 Candida tropicalis strains. Biofilms were developed in 96-well, flat-bottomed microtiter plates for 48 hours. A synergistic effect between amphotericin B and clarithromycin was demonstrated against 66.6% of C. parapsilosis, 66.6% of C. glabrata, and 42.8% of C. albicans biofilms. A synergistic effect between amphotericin B and rifampin was demonstrated against 66.6% of C. parapsilosis, 42.8% of C. albicans, and 33.3% of C. glabrata biofilms. No synergistic effect was observed against C. krusei or C. tropicalis biofilms with any of the combinations. Rifampin or clarithromycin alone did not exert any effect on Candida species biofilms. Rifampin or clarithromycin combinations with amphotericin B might be of interest in the treatment of Candida biofilm-related infections.

[Scientific evidence supporting the use of micafungin in the treatment of invasive candidiasis]

Micafungin is a semisynthetic lipopeptide developed from Coleophoma empetri, which blocks the synthesis of β-1,3-D-glucan, an essential component of the fungal wall, though non-competitive inhibition of β-1,3-D-glucan synthetase. Micafungin is a dose-dependent candidacidal agent with excellent in vitro efficacy against most Candida spp. including species resistant to amphotericin B, such as Candida lusitaniae, several azoles, such as C. glabrata or C. krusei, and isolates not susceptible to other echinocandins. Moreover, this drug is active against Candida biofilms. Micafungin is a first-line drug for the treatment of candidemias and invasive candidiasis in adults and children (including neonates). This drug is approved for use in the treatment of invasive candidiasis and Candida esophagitis, as well as in the prophylaxis of Candida infections in hematopoietic stem cell transplant recipients or those at risk of prolonged neutropenia. Micafungin can be used both in the treatment and prevention of candidiasis in neonates, children, adolescents, adults, and the elderly, making it highly useful in patient groups in which the use of other antifungal drugs has not been authorized.

Detailed comparison of Candida albicans and Candida glabrata biofilms under different conditions and their susceptibility to caspofungin and anidulafungin

Candida biofilm development can be influenced by diverse factors such as substrate, culture medium, carbohydrate source and pH. We have analysed biofilm formation of Candida albicans SC5314 and Candida glabrata ATCC 2001 wild-type strains in the presence of different media (RPMI 1640 versus YNB) and using different pH values (pH 5.6 or 7.0). We determined adhesion and biofilm formation on polystyrene, changes in the expression of adhesin genes during these processes and the susceptibility of mature biofilms to echinocandins. Biofilms formed on polystyrene by both Candida species proved to be influenced strongly by the composition of the medium rather than pH. C. albicans and C. glabrata formed thicker biofilms in RPMI 1640 medium, whereas in YNB medium, both species manifested adhesion rather than characteristic multilayer biofilm architecture. The stimulated biofilm formation in RPMI 1640 medium at pH 7.0 corroborated positively with increased expression of adhesin genes, essential to biofilm formation in vitro, including ALS3 and EAP1 in C. albicans and EPA6 in C. glabrata. The thicker biofilms grown in RPMI 1640 medium were more tolerant to caspofungin and anidulafungin than YNB-grown biofilms. We also observed that mature C. glabrata biofilms were less susceptible in RPMI 1640 medium to echinocandins than C. albicans biofilms. Environmental conditions, i.e. medium and pH, can significantly affect not only biofilm architecture, but also the expression profile of several genes involved during the different stages of biofilm development. In addition, growth conditions may also influence the antifungal-susceptibility profile of fungal populations within biofilm structures. Therefore, before designing any experimental biofilm set-up, it is important to consider the potential influence of external environmental factors on Candida biofilm development.

In vitro effectiveness of antifungal lock solutions on catheters infected with Candida species

The antibiotic lock technique involves filling the catheter lumen with an antibiotic solution and allowing it to dwell for sufficient time to sterilize the infected device. However, antifungal therapy for treating catheter-related fungal infection in this setting is unknown. In this study, the effectiveness of the commercially available antifungal drugs, which are commonly used in candidemia, were assessed in an in vitro antibiotic lock model. Amphotericin B, caspofungin, fluconazole, itraconazole, and voriconazole were used as lock solutions against catheters infected with slime-forming Candida albicans and Candida parapsilosis. Infected catheters were exposed to each of the antifungal lock solution (300-, 500- and 1,000-fold MIC) for 1, 3, 5, and 7 days. The presence of the remaining Candida in the catheter was evaluated quantitatively. Among the antifungal agents, amphotericin B and caspofungin lock solutions decreased the yeast colony count significantly from baseline starting on the first day of treatment (P < 0.001). Significant decrease in the colony count continued, and the catheters were completely sterile at the fifth day. Fluconazole, itraconazole, and voriconazole lock solutions failed to sterilize the catheters, and the numbers of yeast colonies were >10(5) at the end of the study. In summary, amphotericin B and caspofungin appear to have unique activities against Candida-infected catheters. It seems that one of these drugs may permit the retention of an affected intravascular catheter by sterilizing it in a few days.

In vitro evaluation of antibiotic lock technique for the treatment of Candida albicans, C. glabrata, and C. tropicalis biofilms

Candidaemia associated with intravascular catheter-associated infections is of great concern due to the resulting high morbidity and mortality. The antibiotic lock technique (ALT) was previously introduced to treat catheter-associated bacterial infections without removal of catheter. So far, the efficacy of ALT against Candida infections has not been rigorously evaluated. We investigated in vitro activity of ALT against Candida biofilms formed by C. albicans, C. glabrata, and C. tropicalis using five antifungal agents (caspofungin, amphotericin B, itraconazole, fluconazole, and voriconazole). The effectiveness of antifungal treatment was assayed by monitoring viable cell counts after exposure to 1 mg/mL solutions of each antibiotic. Fluconazole, itraconazole, and voriconazole eliminated detectable viability in the biofilms of all Candida species within 7, 10, and 14 days, respectively, while caspofungin and amphotericin B did not completely kill fungi in C. albicans and C. glabrata biofilms within 14 days. For C. tropicalis biofilm, caspofungin lock achieved eradication more rapidly than amphotericin B and three azoles. Our study suggests that azoles may be useful ALT agents in the treatment of catheter-related candidemia.