Candida Albicans
Genital Microbioma

The most frequent opportunistic infections found in patients with diabetes is buccal candidiasis. Candida Albicans is microorganism naturally found in the oral cavity, it grows rapidly when diabetes causes alterations in saliva's composition like reduction of salivary flow or reduction of salivary antimicrobials factors. The risk of buccal candidiasis among diabetics that use dentures is significantly higher than among dentate patients.

Candida is the most common human fungal pathogen that causes a variety of afflictions from superficial mucosal infections to deep mycoses. Biofilm formation is a major virulence factor of Candida. In nature, the yeast exist in a mixed milieu either in the oral cavity or in other habitats with a multitude of bacteria colonising mucosal surfaces within a shared community. The underlying mechanisms of these interactions appear to depend on several factors relating to biofilm development, such as species and strains of organisms, nutritional factors, aerobiosis and related environmental factors. Although the fundamental nature of these interactions appears to be commensalism and antagonism, the emerging evidence based on novel molecular, proteomic and imaging tools indicates these biological mechanisms to be far more complex than hitherto recognised.

CANDIDA’S INTERACTION WITH HOST

Candida species are commensal fungal organisms as well as opportunistic pathogens of mucosal tissues. From the commensal relationship, most healthy individuals have demonstrable Candida-specific immunity.

Then, why should some people develop a disease?

The answer may stay in the balance between factors of virulence and on the other hand immunologic defenses of our body. At the same time each microorganism is placed in a micro environment sharing the same substrates needed for their growth. A variety of yeasts grow as a normal flora on mucosal surfaces. These yeasts are controlled by the immune response, pH and carbohydrate availability, as well as by bacterial that compete with yeasts for mucosal surfaces. When normal conditions change, yeasts may spread across mucosal surface, and they may disseminate in immunocompromised patients.

A-MECHANISMS OF PATHOGENICITY:

Superficial structures:

Receptors of complement:

Enzymes:

• hydrolysis of guest’s protections, competition for substrates

Emolysines, siderophores:

1. FIMBRIE:

   The fimbria is a glycoprotein made for 80-85% by carbohydrates, specially d-mannose, and 20-25% by proteins (50% hydrophobic residuals). Fimbrias interact with cellular glicosphingolipidic receptors.

2. MANNAN
   
   

   Mannan is a glycoprotein with polymers and oligomers of mannose. Its composition changes in relation to the specie. Mannoproteins recognize carbohydrates of endothelial and epithelial cells trough a lectina-like interaction. Moreover, mannan suppress or promotes cellular immunity. They play major virulence and immunogenic roles with both their mannan and protein moieties. The 65-kDa mannoprotein (MP65) of Candida albicans is a beta-glucanase adhesin recognized as a major target of the human immune response against this fungus.

   
   
3. ADHESINS

   Adhesins are glicomannoproteins placed over the cell wall surface. There is a wide number of different types of adhesins, according to specie, phenotype, dismorphism of Candida, temperature, pH, presence of antimycotics or other microorganisms. Adhesivity depends on protein-protein links: integrine analogous (receptor of C3), fibronectine, laminine. And also Lectina like links (interaction with fucose or N-acetilglucosammine).

4. COMPLEMENT AND VIRULENCE


• Receptors of iC3 (which bind inactivated C3) rise up in presence of high values of glucose ( major sensibility to infection for diabetic patients?)
• Riduction of phagocitosys
• Switching into virulent specie
5. ENZYMES

C.Albicans produces several enzymes involved in the pathogenesis of Candidiasis. Among these are various proteases, phospholipases,  lysophopspholipases. They are stored into vacuoles and their amount changes in relation to nutritive substrate. In particular Aspartil proteinases which is active at acid pH towards different proteins (albumine, Hb, casein, keratin, collagene, heavy chains of IgA1 and IgA2); this mechanism contributes to adhesivity and invasivity. . Otherwise it destroys cistatine A of human cute which has a protective role against exogenous pathogens. Candida albicans can use proteins as the sole source of nitrogen for growth. The secretion of aspartic proteinases, which have been shown to contribute to virulence of C. albicans, allows the fungus to digest host proteins to produce peptides that must be taken up into the cell by specific transporters. Phospholipases A,B,C and lysophospolypases may be involved in remodelling of the cell wall during the growth and invasion of host. Extracellular collagenases destroys soluble and insoluble collagene, piruvate-Kinase, Alcol-Dh involved in immunological response.

Group V secretory phospholipase A2 modulates phagosome maturation and regulates the innate immune response against Candida albicans.

Phospholipases of Candida albicans.

6. EMOLYTHIC FACTORS

   C.Albicans has emolythic activity on Agar blood, with complement opsonised red blood cells. This propriety  is a way to gain iron from the environment trough superficial receptors of complement. Use of iron by Candida is another expression of pathogenicity and is reduced by Hb, Ferritine, Trasferrine, Lactoferrine.
7. WITCHING
   Recent advances indicate that C. albicans uses a common set of conserved pathways to regulate dimorphism, mating and phenotypic switching. Major pathways known to regulate dimorphism include a mitogen-activated protein (MAP) kinase pathway through Cph1, the cAMP-dependent protein kinase pathway via Efg1, and Tup1-mediated repression through Rfg1 and Nrg1. The Cph1-mediated MAP kinase pathway is critical for the mating process, while all three pathways are implicated in the regulation of white-opaque switching. All these developmental pathways regulate the expression of hypha-specific and/or phase-specific genes. A high proportion of hypha-specific genes and phase-specific genes encode proteins that contribute directly or indirectly to pathogenesis and virulence of C. albicans. Therefore, virulence genes are co-regulated with cell morphogenesis. This supports a previous notion that the unique aspects of C. albicans commensalism and pathogenesis may lie in the developmental programs of dimorphism and phenotypic switching.

B-HOST’S ROLE

Candida albicans is a member of the normal human microflora. C. albicans cell wall is composed of several protein and carbohydrate components which have been shown to play a crucial role in C. albicans interaction with the host immune system. Major components of C. albican cell wall are carbohydrates such as mannans, beta glucans and chitins, and proteins that partially modulate the host immune responses. Dendritic cells (DC), as the most important antigen-presenting cells of the immune system, play a critical role in inducing immune responses against different pathogens.

Candida species are commensal fungal organisms as well as opportunistic pathogens of mucosal tissues. From the commensal relationship, most healthy individuals have demonstrable Candida-specific immunity. In immunocompromised persons, however, fungal infections caused primarily by C. albicans often occur. In HIV disease, up to 90% of HIV+ persons will have a symptomatic episode of oropharyngeal candidiasis (OPC) sometime during progression to AIDS, many of which become recurrent. In contrast, vulvovaginal candidiasis (VVC) and systemic Candida infections (candidaemia) are much less common during HIV disease, indicating the diversity and compartmentalization of the host response to Candida. Both innate resistance and acquired immunity play some role in maintaining C. albicans in the commensal state and protecting the systemic circulation. Polymorphonuclear leukocytes (PMNL) are critical for protection against systemic infections, whereas cell-mediated immunity (CMI) by Th1-type CD4+ T-cells is important for protection against mucosal infections. However, there is a discordant role for CMI at the vaginal versus oral mucosa, whereas little to no role for local or systemic CMI is evident at the vaginal mucosa. In contrast, there is a strong correlation between reduced blood CD4+ cells and the incidence of OPC, but it remains unclear whether systemic or local CMI is more important.

Evaluation of systemic CMI in a cohort of HIV+ individuals with and without mucosal candidiasis revealed that Candida-specific CMI is not different between HIV+ persons with OPC or VVC and HIV- persons. Thus, the correlation of reduced CD4+ cell numbers to OPC may be explained by the requirement for a threshold number of systemic CD4+ cells to protect the oral mucosa together with the status of local immunity. Indeed, HIV+ persons with and without OPC had a Th2-type salivary cytokine profile suggestive of susceptibility to Candida infection compared with a protective Th0/Th1-type profile in HIV- persons. Candida-specific antibodies, although present, are controversial relative to a role in protection or eradication of infection. While studies of mucosal innate resistance are limited, we recently found that epithelial cells from saliva and vaginal lavages of healthy individuals inhibit the growth of Candida in vitro. This epithelial cell anti-Candida activity requires cell contact by viable cells with no role for soluble factors, including saliva. Interestingly, oral epithelial cells from HIV+ persons with OPC had significantly reduced activity, indicating some protective role for the epithelial cells. Taken together, these data suggest that immunity to Candida is site-specific, compartmentalized and involves innate and/or acquired mechanisms from systemic and/or local sources.

CANDIDA: A DOUBLE FACE MICROORGANISM

C.Albicans has a particular property: dimorphism. It can exist under two shapes, blastospores and ife. Blastospores are eukariotic cells with a cell wall, commonly placed as groups in the oral cavity and in the gut. Blastospores reproduce themselves trough a sexual way, generating daughter cells. Ife could be described as microscopic tubes containing several cellular units parted by septa, there is a big amount of them during infection, than it’s thought to be a index of micotic aggressiveness.
When, in presence of adverse environmental conditions, an enlargement of adsorption surface is needed,  Candida produces pseudoife, chains of cells which are united but still independent. The difference with ife is that pseudoife have pores of communication between cells. Pseudoife can be described as the aggressive face of Candida. In very hard environments, rarely in humans, Candida can generate forms of resistance, clamidospores, big spores with a double wall and very low methabolism. The concept is that the morphologic expression depends on environmental conditions and that these changes of Candida can be included as part of the “switching”. 

At least four positive (arrowheads) and two negative (bars) pathways control morphological transitions in Candida albicans. The pathways that promote the switch from yeast to pseudohyphal and hyphal growth are shown as follows: MAP-kinase pathway in pink, cAMP pathway in green, Cph2 pathway in grey, Rim101 pH response pathway in blue and Czf1 matrix pathway in orange. Pathways that inhibit this switch are the Tup1–Nrg1–Rpg1 pathway in red and the Rbf1 pathway in purple. HSGs, hyphal-specific genes.

Effect of phenotypic switching on expression of virulence factors by Candida albicans causing candidiasis in diabetic patients. 

Environmental induction of white-opaque switching in Candida albicans.

Phenotypic switching and its influence on expression of virulence factors by Candida albicans causing candidiasis in human immunodeficiency virus-infected patients.

Polymorphism of Candida albicans is a major factor in the interaction with human dendritic cells.

 

 

 

HOW DO THESE FACTORS ACT IN VIVO?

OTHER ACTORS INVOLVED IN THE MICROENVIRONMENT

Hemoglobin is an effective inducer of hyphal differentiation in Candida albicans 2007

Microbiol Immunol. 1995;39(6):405-9.
Suppression of anti-Candida activity of murine neutrophils by progesterone in vitro: a possible mechanism in pregnant women's vulnerability to vaginal candidiasis.

Nohmi T, Abe S, Dobashi K, Tansho S, Yamaguchi H.

Department of Microbiology and Immunology, Teikyo University School of Medicine, Tokyo, Japan.
Abstract

Sex steroid hormones were examined for their effect on mycelial growth of Candida albicans, and the inhibitory activity of casein-induced murine peritoneal neutrophils against mycelial growth of C. albicans was examined in vitro using a crystal violet staining method or a [3H]glucose incorporation method. Four steroid hormones, danazol, estradiol, estriol and testosterone had no effect on mycelial growth of C. albicans, but progesterone appeared to convert the growth form of C. albicans from hyphal to yeast. Danazol (10(-6) M) and progesterone (10(-5) M) suppressed anti-Candida activity of neutrophils of non-treated mice, while testosterone, estradiol, and estriol did not. The anti-Candida activity of neutrophils of estradiol-pretreated mice was clearly suppressed by progesterone even at 10(-6) M which corresponded to its plasma concentration in pregnant women in the third trimester. The physiological significance of this suppressive effect of progesterone was discussed in relation to the vulnerability of pregnant women to vaginal candidiasis.

Balancing inflammation and tolerance in vivo through dendritic cells by the commensal Candida albicans. 2009

Vitamin A deficiency reduces liver and colon docosahexaenoic acid levels in rats fed high linoleic and low alpha-linolenic acid diet.

PLoS Pathog. 2008 Nov;4(11):e1000217. Epub 2008 Nov 21.
The hyphal-associated adhesin and invasin Als3 of Candida albicans mediates iron acquisition from host ferritin. 2008

Almeida RS, Brunke S, Albrecht A, Thewes S, Laue M, Edwards JE, Filler SG, Hube B.

Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for Natural Product Research and Infection Biology, Hans Knoell Institute, Jena, Germany.

Iron sequestration by host iron-binding proteins is an important mechanism of resistance to microbial infections. Inside oral epithelial cells, iron is stored within ferritin, and is therefore not usually accessible to pathogenic microbes. We observed that the ferritin concentration within oral epithelial cells was directly related to their susceptibility to damage by the human pathogenic fungus, Candida albicans. Thus, we hypothesized that host ferritin is used as an iron source by this organism. We found that C. albicans was able to grow on agar at physiological pH with ferritin as the sole source of iron, while the baker's yeast Saccharomyces cerevisiae could not. A screen of C. albicans mutants lacking components of each of the three known iron acquisition systems revealed that only the reductive pathway is involved in iron utilization from ferritin by this fungus. Additionally, C. albicans hyphae, but not yeast cells, bound ferritin, and this binding was crucial for iron acquisition from ferritin. Transcriptional profiling of wild-type and hyphal-defective C. albicans strains suggested that the C. albicans invasin-like protein Als3 is required for ferritin binding. Hyphae of an Deltaals3 null mutant had a strongly reduced ability to bind ferritin and these mutant cells grew poorly on agar plates with ferritin as the sole source of iron. Heterologous expression of Als3, but not Als1 or Als5, two closely related members of the Als protein family, allowed S. cerevisiae to bind ferritin. Immunocytochemical localization of ferritin in epithelial cells infected with C. albicans showed ferritin surrounding invading hyphae of the wild-type, but not the Deltaals3 mutant strain. This mutant was also unable to damage epithelial cells in vitro. Therefore, C. albicans can exploit iron from ferritin via morphology dependent binding through Als3, suggesting that this single protein has multiple virulence attributes.

Candida Albicans

Farnesol

Release from quorum-sensing molecules triggers hyphal formation during Candida albicans resumption of growth. 2005

Sterol synthesis and drug resistance association

Eukaryot Cell. 2009 Aug;8(8):1174-83. Epub 2009 Jun 19.
Role of Ndt80p in sterol metabolism regulation and azole resistance in Candida albicans. 2009

Sellam A, Tebbji F, Nantel A.

The Ndt80p transcription factor modulates azole tolerance in Candida albicans by controlling the expression of the gene for the drug efflux pump Cdr1p. To date, the contribution of this transcriptional modulator to drug tolerance is not yet well understood. Here, we investigate the role of Ndt80p in mediating fluconazole tolerance by determining its genome-wide occupancy using chromatin immunoprecipitation coupled to high-density tiling arrays. Ndt80p was found to bind a large number of gene promoters with diverse biological functions. Gene ontology analysis of these Ndt80p targets revealed a significant enrichment in gene products related to the cell wall, carbohydrate metabolism, stress responses, hyphal development, multidrug transport, and the cell cycle. Ndt80p was found on the promoters of ergosterol biosynthesis genes, including on the azole target Erg11p. Additionally, expression profiling was used to identify fluconazole-responsive genes that require Ndt80p for their proper expression. We found that Ndt80p is crucial for the expression of numerous fluconazole-responsive genes, especially genes involved in ergosterol metabolism. Therefore, by combining genome-wide location and transcriptional profiling, we have characterized the Ndt80p fluconazole-dependent regulon and demonstrated the key role of this global transcriptional regulator in modulating sterol metabolism and drug resistance in C. albicans.

On the basis of EQ>/<W/0.1 we can suppose an homology with:

• CCNB3_HUMAN (more mitosis than meiosis)
• CLSPN_HUMAN