Adapting to survive: How Candida overcomes host-imposed constraints during human colonization.

Successful human colonizers such as Candida pathogens have evolved distinct strategies to survive and proliferate within the human host. These include sophisticated mechanisms to evade immune surveillance and adapt to constantly changing host microenvironments where nutrient limitation, pH fluctuations, oxygen deprivation, changes in temperature, or exposure to oxidative, nitrosative, and cationic stresses may occur. Here, we review the current knowledge and recent findings highlighting the remarkable ability of medically important Candida species to overcome a broad range of host-imposed constraints and how this directly affects their physiology and pathogenicity. We also consider the impact of these adaptation mechanisms on immune recognition, biofilm formation, and antifungal drug resistance, as these pathogens often exploit specific host constraints to establish a successful infection. Recent studies of adaptive responses to physiological niches have improved our understanding of the mechanisms established by fungal pathogens to evade the immune system and colonize the host, which may facilitate the design of innovative diagnostic tests and therapeutic approaches for Candida infections.

The Elusive Anti-Candida Vaccine: Lessons From the Past and Opportunities for the Future.

Candidemia is a bloodstream fungal infection caused by Candida species and is most commonly observed in hospitalized patients. Even with proper antifungal drug treatment, mortality rates remain high at 40-50%. Therefore, prophylactic or preemptive antifungal medications are currently recommended in order to prevent infections in high-risk patients. Moreover, the majority of women experience at least one episode of vulvovaginal candidiasis (VVC) throughout their lifetime and many of them suffer from recurrent VVC (RVVC) with frequent relapses for the rest of their lives. While there currently exists no definitive cure, the only available treatment for RVVC is again represented by antifungal drug therapy. However, due to the limited number of existing antifungal drugs, their associated side effects and the increasing occurrence of drug resistance, other approaches are greatly needed. An obvious prevention measure for candidemia or RVVC relapse would be to immunize at-risk patients with a vaccine effective against Candida infections. In spite of the advanced and proven techniques successfully applied to the development of antibacterial or antiviral vaccines, however, no antifungal vaccine is still available on the market. In this review, we first summarize various efforts to date in the development of anti-Candida vaccines, highlighting advantages and disadvantages of each strategy. We next unfold and discuss general hurdles encountered along these efforts, such as the existence of large genomic variation and phenotypic plasticity across Candida strains and species, and the difficulty in mounting protective immune responses in immunocompromised or immunosuppressed patients. Lastly, we review the concept of "trained immunity" and discuss how induction of this rapid and nonspecific immune response may potentially open new and alternative preventive strategies against opportunistic infections by Candida species and potentially other pathogens.

Oral Administration of Human Polyvalent IgG by Mouthwash as an Adjunctive Treatment of Chronic Oral Candidiasis.

Candida albicans is a commensal fungus that can cause disease ranging in severity from moderate to severe mucosal infections to more serious life-threating disseminated infections in severely immunocompromised hosts. Chronic mucocutaneous candidiasis (CMC) occurs in patients with mutations in genes affecting IL-17-mediated immunity, such as STAT3, AIRE, RORC, CARD9, IL12B, and IL12RB1, or gain of function (GOF) mutations in STAT1. New strategies for the treatment of candidiasis are needed because of the increased burden of infections and the emergence of drug-resistant strains. In this study, we investigated an aspect of the role of antibodies in the control of C. albicans infection. We tested in vitro the effects of C. albicans opsonization with commercial human polyvalent intravenous IgG (IV IgG) on NADPH oxidase activity and killing of the fungi by blood leukocytes from 11 healthy donors and found a significant enhancement in both phenomena that was improved by IV IgG opsonization. Then, we hypothesized that the opsonization of Candida in vivo could help its elimination by mucosal phagocytes in human patients with mucocutaneous candidiasis. We tested a novel adjunctive treatment for oral candidiasis in humans based on topical treatment with IV IgG. For this purpose, we choose two pediatric patients with well-characterized primary immunodeficiencies who are susceptible to CMC. Two 8-year-old female patients with an autosomal recessive mutation in the IL12RB1 gene (P1, with oral candidiasis) and a GOF mutation in STAT1 (P2, with severe CMC persistent since the age of 8 months and resistant to pharmacological treatments) were treated with IV IgG administered daily three times a day as a mouthwash over the course of 2 weeks. The treatment with the IV IgG mouthwash reduced C. albicans mouth infection by 98 and 70% in P1 and P2, respectively, after 13 days, and complete fungal clearance was observed after complementary nystatin and caspofungin treatments, respectively. Therefore, treatment of oral candidiasis with human polyvalent IgG administered as a mouthwash helps eliminate mucosal infection in humans, circumventing drug resistance, and opening its potential use in patients with primary or transient immunodeficiency.

The role of epidemiological cutoff values (ECVs/ECOFFs) in antifungal susceptibility testing and interpretation for uncommon yeasts and moulds / Utilidad clínica de los puntos de corte epidemiológicos (ECVs/ECOFFs) para interpretar los datos de la sensibilidad antifúngica de los mohos y levaduras de poca prevalencia

The role of antimicrobial susceptibility testing is to aid in selecting the best agent for the treatment of bacterial and fungal diseases. This has been best achieved by the setting of breakpoints by Clinical Laboratory Standards Institute (CLSI) for prevalent Candida spp. versus anidulafungin, caspofungin, micafungin, fluconazole, and voriconazole. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) also has set breakpoints for prevalent and common Candida and Aspergillus species versus amphotericin B, itraconazole, and posaconazole. Recently, another interpretive category, the epidemiological cut off value, could aid in the early identification of strains with acquired resistance mechanisms. CLSI has postulated that epidemiological cut off values may, with due caution, aid physicians in managing mycosis by species where breakpoints are not available. This review provides (1) the criteria and statistical approach to establishing and estimating epidemiological cut off values (ECVs), (2) the role of the epidemiological cut off value in establishing breakpoints, (3) the potential role of epidemiological cut off values in clinical practice, (4) and the wide range of CLSI-based epidemiological cut off values reported in the literature as well as EUCAST and Sensititre Yeast One-ECVs. Additionally, we provide MIC/MEC (minimal inhibitory concentrations/minimum effective concentrations) ranges/modes of each pooled distribution used for epidemiological cut off value calculation. We focus on the epidemiological cut off value, the new interpretive endpoint that will identify the non-wild type strains (defined as potentially harboring resistance mechanisms). However, we emphasize that epidemiological cut off values will not categorize a fungal isolate as susceptible or resistant as breakpoints do, because the former do not account for the pharmacology of the antifungal agent or the findings from clinical outcome studies (AU)

Las pruebas de sensibilidad a los antimicrobianos tienen como finalidad ayudar en la selección del mejor fármaco para el tratamiento de las infecciones fúngicas y bacterianas. El establecimiento de puntos de corte para la anidulafungina, la caspofungina, la micafungina, el fluconazol y el voriconazol en las especies de Candida más prevalentes por parte del Clinical and Laboratory Standards Institute (CLSI) permite alcanzar este objetivo. El European Committee on Antimicrobial Susceptibility Testing (EUCAST) también ha establecido puntos de corte para la anfotericina B, el itraconazol y el posaconazol en las especies más comunes de Candida y Aspergillus. En los últimos tiempos se ha propuesto una nueva categoría, la de los puntos de corte epidemiológicos, que puede ayudar a identificar de manera temprana los aislamientos que han adquirido mecanismos de resistencia. Según el CLSI los puntos de corte epidemiológicos podrían, con la debida cautela, ayudar a los médicos en la selección del tratamiento en aquellas micosis causadas por especies para las que no se han establecido puntos de corte. Esta revisión repasa: 1) los criterios y la aproximación estadística seguida para establecer y estimar los puntos de corte epidemiológicos, 2) el papel de los puntos de corte epidemiológicos para establecer los puntos de corte, 3) el papel de los puntos de corte epidemiológicos en la práctica clínica, y 4) el amplio rango de puntos de corte epidemiológicos que aparecen en la literatura establecidos mediante los métodos del CLSI, EUCAST o Sensititre® YeastOne®. Se muestran también los rangos de las concentraciones mínimas inhibitorias (CMI) y concentraciones mínimas efectivas (CME) utilizados para el cálculo de los puntos de corte epidemiológicos. Incidimos de manera especial sobre estos últimos por tratarse de una nueva interpretación de los CMI y los CME que permite identificar aquellos aislamientos que no son salvajes y potencialmente resistentes. No obstante, insistimos en que los puntos de corte epidemiológicos no pueden utilizarse para calificar como resistente o sensible a un determinado aislamiento, como lo hacen los puntos de corte, puesto que los puntos de corte epidemiológicos no se rigen por las características farmacológicas de los agentes antifúngicos ni por la evolución clínica de los pacientes (AU)

[Characteristics of filamentous fungal biofilms and their roles in ophthalmology].

A filamentous fungal biofilm is a collection of hyphae and spores encased in a matrix, which has distinct developmental phases governed by complex molecular events. Resistance to antifungal drugs and components of the innate immune system remain the greatest threats to patients with filamentous fungal biofilms. There is increasing evidence that filamentous fungal biofilms play a role in a variety of ocular infections. Filamentous fungal biofilms may participate in ocular infections by allowing filamentous fungi to persist on abiotic surfaces that come in contact with the eye, and by direct biofilm formation on biotic surfaces of the eye. This review discusses the current understanding of the basic biology and clinical implications associated with filamentous fungal biofilms in ophthalmology.

Immunotherapy: a potential adjunctive treatment for fungal infection.

PURPOSE OF REVIEW: Invasive and mucosal candidiasis are associated with major morbidity in patients with inappropriate host defence mechanisms. This review focuses on recent studies elucidating the immune response against candidiasis and possible immunotherapeutic approaches. RECENT FINDINGS: The last year has seen substantial advances in understanding antifungal immunity. The role of pattern recognition receptors and the Th1 and Th17 immune pathways has been further elucidated. The first genome-wide studies have identified new risk factors for candidaemia. Trials of adjuvant immunotherapy for fungal infections have provided directions for the future. SUMMARY: Understanding the fungal pathogenesis and the induction of protective antifungal adaptive immunity has advanced the development of immunotherapeutic strategies and vaccines against invasive and mucosal candidiasis.

Recent insights into Candida albicans biofilm resistance mechanisms.

Like other microorganisms, free-living Candida albicans is mainly present in a three-dimensional multicellular structure, which is called a biofilm, rather than in a planktonic form. Candida albicans biofilms can be isolated from both abiotic and biotic surfaces at various locations within the host. As the number of abiotic implants, mainly bloodstream and urinary catheters, has been increasing, the number of biofilm-associated bloodstream or urogenital tract infections is also strongly increasing resulting in a raise in mortality. Cells within a biofilm structure show a reduced susceptibility to specific commonly used antifungals and, in addition, it has recently been shown that such cells are less sensitive to killing by components of our immune system. In this review, we summarize the most important insights in the mechanisms underlying biofilm-associated antifungal drug resistance and immune evasion strategies, focusing on the most recent advances in this area of research.

Growth of Candida albicans cells on the physiologically relevant carbon source lactate affects their recognition and phagocytosis by immune cells.

Candida albicans is a normal resident of the human gastrointestinal and urogenital tracts and also a prevalent fungal pathogen. During both commensalism and infection, it must match the immunological defenses of its host while adapting to environmental cues and the local nutrient status. C. albicans regularly colonizes glucose-poor niches, thereby depending upon alternative carbon sources for growth. However, most studies of host immune responses to C. albicans have been performed on fungal cells grown on glucose, and the extent to which alternative physiologically relevant carbon sources impact innate immune responses has not been studied. The fungal cell wall is decorated with multifarious pathogen-associated molecular patterns and is the main target for recognition by host innate immune cells. Cell wall architecture is both robust and dynamic, and it is dramatically influenced by growth conditions. We found that growth of C. albicans cells on lactate, a nonfermentative carbon source available in numerous anatomical niches, modulates their interactions with immune cells and the resultant cytokine profile. Notably, lactate-grown C. albicans stimulated interleukin-10 (IL-10) production while decreasing IL-17 levels, rendering these cells less visible to the immune system than were glucose-grown cells. This trend was observed in clinical C. albicans isolates from different host niches and from different epidemiological clades. In addition, lactate-grown C. albicans cells were taken up by macrophages less efficiently, but they were more efficient at killing and escaping these phagocytic cells. Our data indicate that carbon source has a major impact upon the C. albicans interaction with the innate immune system.

Exogenous pentraxin 3 restores antifungal resistance and restrains inflammation in murine chronic granulomatous disease.

Chronic granulomatous disease (CGD) is a primary immunodeficiency characterized by life-threatening bacterial and fungal infections and hyperinflammation. The susceptibility to aspergillosis in experimental CGD (p47(phox-/-) mice) is associated with the failure to control the inherent inflammatory response to the fungus and to restrict the activation of inflammatory Th17 cells. We assessed whether pentraxin (PTX)3, a member of a family of multimeric pattern-recognition proteins with potent anti-Aspergillus activity, could limit pathogenic inflammation in p47(phox-/-) mice by curbing the IL-23/Th17 inflammatory axis in response to the fungus. We found that the production of PTX3 was delayed in CGD mice in infection but exogenous administration of PTX3 early in infection restored antifungal resistance and restrained the inflammatory response to the fungus. This occurred through down-regulation of IL-23 production by dendritic cells and epithelial cells which resulted in limited expansion of IL-23R+ gammadelta+ T cells producing IL-17A and the emergence of Th1/Treg responses with minimum pathology. Thus, PTX3 could be therapeutically used for the exploitation of NADPH-independent mechanism(s) of antifungal immune protection with limited immunopathology in CGD.

Pruebas moleculares en el diagnóstico micológico / Molecular techniques in mycology

El desarrollo de pruebas moleculares de diagnósticomicológico no ha dejado de aumentar en los últimos añosdebido al incremento en la prevalencia de las infeccionesfúngicas y a la lentitud en alcanzar un diagnósticomediante las técnicas microbiológicas clásicas. Estaspruebas moleculares están diseñadas para resolver lossiguientes aspectos del diagnóstico micológico: a)identificación de especie mediante secuenciación dedianas taxonómicamente relevantes; b) diagnóstico clínicoprecoz de las infecciones fúngicas; c) detección de losmecanismos de resistencia a los antifúngicos, y d)tipificación subespecífica de cepas clínicas. Actualmente, estas metodologías siguen circunscritas a centros de referencia tecnológicamente avanzados. No obstante, parece probable que, en breve, algunas de estas técnicas estarán disponibles en los laboratorios asistenciales

An increasing number of molecular techniques for thediagnosis of fungal infections have been developed in thelast few years, due to the growing prevalence of mycosesand the length of time required for diagnosis when classical microbiological methods are used. These methods are designed to resolve the following aspects of mycological diagnosis: a) Identification of fungi to species level by means of sequencing relevant taxonomic targets; b) early clinical diagnosis of invasive fungal infections; c) detection of molecular mechanisms of resistance to antifungal agents and d) molecular typing of fungi. Currently, these methods are restricted to highly developed laboratories. However, some of these techniques will probably be available in dailyclinical practice in the near future

Symptomatic relapse of HIV-associated cryptococcal meningitis after initial fluconazole monotherapy: the role of fluconazole resistance and immune reconstitution.

BACKGROUND: Cryptococcal meningitis (CM) in South Africa is often treated with fluconazole as initial therapy. Surveillance data suggest that the prevalence of fluconazole-resistant CM is increasing, and expanding access to antiretroviral therapy is resulting in increasing recognition of immune reconstitution inflammatory syndrome. Therefore, we conducted a study to assess the contribution of these factors to CM relapse in this context. METHODS: Patients with symptomatic relapse of CM were prospectively identified at 2 hospitals in Cape Town, South Africa, during the period of 2003-2005. Patients met the following criteria: (1) a previous laboratory-confirmed episode of CM, with resolution of symptoms after treatment; (2) reported adherence to fluconazole treatment; (3) recurrence of typical CM symptoms; (4) cerebrospinal fluid antigen test and/or culture positive for Cryptococcus neoformans; and (5) no alternative diagnosis. Data on patients' human immunodeficiency virus (HIV) and CM infections and treatment were collected and analyzed. RESULTS: Thirty-two episodes of relapse occurred among 27 patients. Episodes were classified into 3 groups: culture-positive episodes in antiretroviral therapy-naive patients (6 episodes), culture-positive episodes in patients receiving antiretroviral therapy (15 episodes), and culture-negative episodes in patients receiving antiretroviral therapy (11 episodes). Seventy-six percent of culture-positive relapses were associated with isolates that had reduced susceptibility to fluconazole. Drug-resistant cases required prolonged intravenous therapy with amphotericin B, and despite this treatment, the mortality rate was high (54% at a median of 6 months of follow-up). Despite a long interval between initiation of antifungal therapy and initiation of antiretroviral therapy (median interval, 144 days), immune reconstitution inflammatory syndrome contributed to at least one-third of relapses. CONCLUSIONS: After initial treatment with fluconazole, relapses of symptomatic CM are often associated with fluconazole resistance and immune reconstitution inflammatory syndrome. These data add to concern about the efficacy of fluconazole, compared with amphotericin B, for initial treatment of HIV-associated CM.

Fluconazole susceptibility of Candida species in Singapore by disc diffusion test.

INTRODUCTION: Resistance of Candida species to fluconazole has been increasingly reported worldwide. To date, the prevalence of resistance to fluconazole in Singapore is unknown. The aim of this study was to use a newly described agar disc diffusion method to study levels of susceptibility of Candida species to fluconazole in several hospitals in Singapore. MATERIALS AND METHODS: Three hundred and ninety Candida isolates from clinical specimens collected from different sites were tested, of which 191 isolates (49.0%) were C. albicans, 69 (17.7%) were C. parapsilosis, 59 (15.1%) were C. glabrata, 51 (13.1%) were C. tropicalis and 4 (1.0%) were C. krusei. Susceptibility testing was performed using 25 micrograms fluconazole discs and standard Mueller-Hinton agar supplemented with 2% glucose and 0.5 microgram/mL of methylene blue. RESULTS: Overall, 381 (97.7%) isolates were susceptible, 6 (1.5%) were susceptible dose-dependent, and 3 (0.8%) were resistant to fluconazole. Of the individual species, 99.5% of C. albicans, 93.2% of C. glabrata, 0% of C. krusei, and 100% of C. parapsilosis, C. tropicalis and other Candida species were susceptible. CONCLUSION: The resistance of Candida species to fluconazole, as measured using a new disc diffusion method, is low in Singapore, with the exception of C. krusei. Fluconazole remains a useful agent for the treatment of candidiasis in this country.