Scott G. Filler

Clinical Practice Guidelines for the Management of Candidiasis: 2009 Update by the Infectious Diseases Society of America

Guidelines for the management of patients with invasive candidiasis and mucosal candidiasis were prepared by an Expert Panel of the Infectious Diseases Society of America. These updated guidelines replace the previous guidelines published in the 15 January 2004 issue of Clinical Infectious Diseases and are intended for use by health care providers who care for patients who either have or are at risk of these infections. Since 2004, several new antifungal agents have become available, and several new studies have been published relating to the treatment of candidemia, other forms of invasive candidiasis, and mucosal disease, including oropharyngeal and esophageal candidiasis. There are also recent prospective data on the prevention of invasive candidiasis in high-risk neonates and adults and on the empiric treatment of suspected invasive candidiasis in adults. This new information is incorporated into this revised document.

Guidelines for Treatment of Candidiasis

Peter G. Pappas, John H. Rex, Jack D. Sobel, Scott G. Filler, William E. Dismukes, Thomas J. Walsh, and John E. Edwards Division of Infectious Diseases, University of Alabama at Birmingham, Alabama; AstraZeneca Pharmaceuticals, Manchester, Great Britain; Wayne State University School of Medicine, Detroit, Michigan; Harbor–University of California-Los Angeles Medical Center, Torrance, California; and Immunocompromised Host Section, Pediatric Oncology Branch, National Cancer Institute, Bethesda, Maryland

Th17 cells and IL-17 receptor signaling are essential for mucosal host defense against oral candidiasis

The commensal fungus Candida albicans causes oropharyngeal candidiasis (OPC; thrush) in settings of immunodeficiency. Although disseminated, vaginal, and oral candidiasis are all caused by C. albicans species, host defense against C. albicans varies by anatomical location. T helper 1 (Th1) cells have long been implicated in defense against candidiasis, whereas the role of Th17 cells remains controversial. IL-17 mediates inflammatory pathology in a gastric model of mucosal candidiasis, but is host protective in disseminated disease. Here, we directly compared Th1 and Th17 function in a model of OPC. Th17-deficient (IL-23p19−/−) and IL-17R–deficient (IL-17RA−/−) mice experienced severe OPC, whereas Th1-deficient (IL-12p35−/−) mice showed low fungal burdens and no overt disease. Neutrophil recruitment was impaired in IL-23p19−/− and IL-17RA−/−, but not IL-12−/−, mice, and TCR-αβ cells were more important than TCR-γδ cells. Surprisingly, mice deficient in the Th17 cytokine IL-22 were only mildly susceptible to OPC, indicating that IL-17 rather than IL-22 is vital in defense against oral candidiasis. Gene profiling of oral mucosal tissue showed strong induction of Th17 signature genes, including CXC chemokines and β defensin-3. Saliva from Th17-deficient, but not Th1-deficient, mice exhibited reduced candidacidal activity. Thus, the Th17 lineage, acting largely through IL-17, confers the dominant response to oral candidiasis through neutrophils and antimicrobial factors.

International Conference for the Development of a Consensus on the Management and Prevention of Severe Candidal Infections

Because of the rapidly increasing incidence of serious candidal infections, a consensus conference of 22 investigators from the United States, Europe, and Japan was held to discuss strategies for the prevention and treatment of deep-organ infections caused by Candida species. Commonly asked questions concerning the management of candidal infections were selected for discussion by the participating investigators. Possible answers to the questions were developed by the investigators, who then voted anonymously for their preferences. In certain instances, unanimity or a strong consensus was the result. In all cases, the full spectrum of responses was recorded and is presented in this report. The forms of candidal infection addressed included candidemia, candiduria, hepatosplenic candidiasis (chronic systemic candidiasis), candidal endophthalmitis, and candidal peritonitis. Prevention and treatment strategies were considered for patients who have undergone surgery, for neutropenic and nonneutropenic patients, and for patients who have undergone bone marrow and solid organ transplantation. The therapeutic roles of amphotericin B (standard and lipid formulations) and the azoles were considered.

Critical role of Bcr1-dependent adhesins in C. albicans biofilm formation in vitro and in vivo.

The fungal pathogen Candida albicans is frequently associated with catheter-based infections because of its ability to form resilient biofilms. Prior studies have shown that the transcription factor Bcr1 governs biofilm formation in an in vitro catheter model. However, the mechanistic role of the Bcr1 pathway and its relationship to biofilm formation in vivo are unknown. Our studies of biofilm formation in vitro indicate that the surface protein Als3, a known adhesin, is a key target under Bcr1 control. We show that an als3/als3 mutant is biofilm-defective in vitro, and that ALS3 overexpression rescues the biofilm defect of the bcr1/bcr1 mutant. We extend these findings with an in vivo venous catheter model. The bcr1/bcr1 mutant is unable to populate the catheter surface, though its virulence suggests that it has no growth defect in vivo. ALS3 overexpression rescues the bcr1/bcr1 biofilm defect in vivo, thus arguing that Als3 is a pivotal Bcr1 target in this setting. Surprisingly, the als3/als3 mutant forms a biofilm in vivo, and we suggest that additional Bcr1 targets compensate for the Als3 defect in vivo. Indeed, overexpression of Bcr1 targets ALS1, ECE1, and HWP1 partially restores biofilm formation in a bcr1/bcr1 mutant background in vitro, though these genes are not required for biofilm formation in vitro. Our findings demonstrate that the Bcr1 pathway functions in vivo to promote biofilm formation, and that Als3-mediated adherence is a fundamental property under Bcr1 control. Known adhesins Als1 and Hwp1 also contribute to biofilm formation, as does the novel protein Ece1.

Als3 Is a Candida albicans Invasin That Binds to Cadherins and Induces Endocytosis by Host Cells

Candida albicans is the most common cause of hematogenously disseminated and oropharyngeal candidiasis. Both of these diseases are characterized by fungal invasion of host cells. Previously, we have found that C. albicans hyphae invade endothelial cells and oral epithelial cells in vitro by inducing their own endocytosis. Therefore, we set out to identify the fungal surface protein and host cell receptors that mediate this process. We found that the C. albicans Als3 is required for the organism to be endocytosed by human umbilical vein endothelial cells and two different human oral epithelial lines. Affinity purification experiments with wild-type and an als3Δ/als3Δ mutant strain of C. albicans demonstrated that Als3 was required for C. albicans to bind to multiple host cell surface proteins, including N-cadherin on endothelial cells and E-cadherin on oral epithelial cells. Furthermore, latex beads coated with the recombinant N-terminal portion of Als3 were endocytosed by Chinese hamster ovary cells expressing human N-cadherin or E-cadherin, whereas control beads coated with bovine serum albumin were not. Molecular modeling of the interactions of the N-terminal region of Als3 with the ectodomains of N-cadherin and E-cadherin indicated that the binding parameters of Als3 to either cadherin are similar to those of cadherin–cadherin binding. Therefore, Als3 is a fungal invasin that mimics host cell cadherins and induces endocytosis by binding to N-cadherin on endothelial cells and E-cadherin on oral epithelial cells. These results uncover the first known fungal invasin and provide evidence that C. albicans Als3 is a molecular mimic of human cadherins.

Combination Polyene-Caspofungin Treatment of Rhino-Orbital-Cerebral Mucormycosis

BACKGROUND It has been axiomatic that echinocandins (e.g., caspofungin) are ineffective against mucormycosis. However, on the basis of preclinical data, we recently began treating rhino-orbital-cerebral mucormycosis (ROCM) with combination polyene-caspofungin therapy. METHODS To determine the impact of polyene-caspofungin therapy, ROCM cases identified by an International Classification of Diseases, Ninth Revision search were retrospectively reviewed to gather data on demographic characteristics, clinical history, and outcomes. The predefined primary end point was success (i.e., the patients was alive and not in hospice care) at 30 days after hospital discharge. RESULTS Forty-one patients with biopsy-proven ROCM were identified over 12 years; 23 (56%) of these patients were Hispanic, and 34 (83%) were diabetic. Patients treated with polyene-caspofungin therapy (6 evaluable patients) had superior success (100% vs. 45%; Pp.02) and Kaplan-Meier survival time (Pp.02), compared with patients treated with polyene monotherapy. Patients treated with amphotericin B lipid complex had inferior success (37% vs. 72%; Pp.03) and a higher clinical failure rate (45% vs. 21%; Pp.04), compared with patients who received other polyenes. However, patients treated with amphotericin B lipid complex plus caspofungin had superior success (100% vs. 20%; Pp.009) and survival time (Pp.01), compared with patients who received amphotericin B lipid complex alone. The benefit of combination therapy, compared with monotherapy, was most pronounced in patients with cerebral involvement (success rate, 100% vs. 25%; Pp.01). In multivariate analysis, only receipt of combination therapy was significantly associated with improved outcomes (odds ratio, 10.9; 95% confidence interval, 1.3- ;Pp.02). CONCLUSIONS Combination polyene-caspofungin therapy represents a promising potential alternative to polyene monotherapy for patients with ROCM. Randomized, prospective investigation of these findings is warranted.

Current Treatment Strategies for Disseminated Candidiasis

The incidence of disseminated candidiasis has increased dramatically over the past several decades. Fortunately, in recent years, a variety of new antifungal agents have become available to treat these infections. On the basis of efficacy, safety, and cost considerations, fluconazole is the agent of choice for the empirical treatment of disseminated candidiasis in nonneutropenic, hemodynamically stable patients, unless a patient is suspected to be infected with an azole-resistant species (i.e., Candida glabrata or Candida krusei). For hemodynamically unstable or neutropenic patients, agents with broader species coverage, such as polyenes, echinocandins, or, possibly, voriconazole, are preferred for empirical treatment of candidemia. Modification of the initial, empirical regimen depends on the response to therapy and the subsequent identification of the species of the offending pathogen. Echinocandins or high-dose polyenes are preferred for the treatment of infections with C. glabrata or C. krusei. Central venous catheters should be removed from all patients who have disseminated candidiasis, if feasible, and antifungal therapy should be administered to all patients who have candidemia or proven candidiasis.

Complementary adhesin function in C. albicans biofilm formation.

BACKGROUND Biofilms are surface-associated microbial communities with significant environmental and medical impact. Here, we focus on an adherence mechanism that permits biofilm formation by Candida albicans, the major invasive fungal pathogen of humans. RESULTS The Als surface-protein family has been implicated in biofilm formation, and we show that Als1 and Als3 have critical but redundant roles. Overexpression of several other Als proteins permits biofilm formation in a biofilm-defective als1/als1 als3/als3 strain, thus arguing that the function of Als proteins in this process is governed by their respective expression levels. The surface protein Hwp1 is also required for biofilm formation, and we find that a mixture of biofilm-defective hwp1/hwp1 and als1/als1 als3/als3 strains can form a hybrid biofilm both in vitro and in vivo in a catheter infection model. Complementary function of Hwp1 and Als1 and 3 seems to reflect their interaction because expression of Hwp1 in the heterologous host S. cerevisiae permits adherence to wild-type C. albicans, but not to an als1/als1 als3/als3 strain. CONCLUSIONS The complementary roles of Hwp1 and Als1 and Als3 in biofilm formation are analogous to the roles of sexual agglutinins in mating reactions. This analogy suggests that biofilm-adhesin complementarity may promote formation of monospecies biofilms.

Candida albicans Als1p: an adhesin that is a downstream effector of the EFG1 filamentation pathway.

Filamentation and adherence to host cells are critical virulence factors of Candida albicans. Multiple filamentation regulatory pathways have been discovered in C. albicans using Saccharomyces cerevisiae as a model. In S. cerevisiae, these pathways converge on Flo11p, which functions as a downstream effector of filamentation and also mediates cell–cell adherence (flocculation). In C. albicans, such effector(s) have not yet been identified. Here, we demonstrate that the cell surface protein Als1p is an effector of filamentation in C. albicans. We show that Als1p expression is controlled by the transcription factor Efg1p, which is known to be a key regulator of filamentation in C. albicans. Further, disruption of ALS1 inhibited filamentation, and autonomous expression of Als1p restored filamentation in an efg1 homozygous null mutant. Thus, Als1p functions as a downstream effector of the EFG1 filamentation pathway. In addition, we found that Als1p mediates both flocculation and adherence of C. albicans to endothelial cells in vitro. As a cell surface glycoprotein that mediates filamentation and adherence, Als1p has both structural and functional similarity to S. cerevisiae Flo11p. Consistent with our in vitro results, Als1p was required for both normal filamentation and virulence in the mouse model of haematogenously disseminated candidiasis.