The Pathogenicity of Fungi - Candida albicans Flashcards
(37 cards)
What two types of infection are caused by c. albicans?
- Superficial infections - oral, vaginal, skin infections
2. Systemic infections - kidney, liver
Where do C. albicans live commensally within the body?
Oral cavity, skin, urinogenital tract, gastrointestinal tract and to a lesser extent the respiratory system.
What is the disease caused by C. albican infection of the oral cavity?
Oral candidiasis
Who is at risk of developing oral candidiasis?
- Immunocompromised individuals such as HIV patients.
- use of dentures
- old age
What disease is caused by c. albican infection of the vula and vagina?
Vulvovaginal candidiasis
What five factors predispose an individual to vulvovaginal candidiasis?
- Diabetes Mellitus
- Antibiotic use
- Oral contraception
- Pregnancy
- Hormone therapy
What causes C. albicans to develop from a non-lethal superficial infection to a lethal systemic infection?
5 causes listed
- Neutropenia
- Damage to gastrointestinal mucosa.
- Central venous catheters allowing direct access to the bloodstream
- Broad spectrum antibacterials allowing for overgrowth of the fungus
- Gastrointestinal surgery which disrupts mucosal barrier
Mention a few known virulence factors of C. albicans.
- Morphological transition between yeast and hyphal forms
- Adhesins and invasins present on the C. albican cell surface
- Thigmotropism (movement in response to stimuli)
- Biofilm formation
- Phenotypic switching
- Secretion of hydrolytic enzymes
What factors cause C. albicans to grow in the yeast form in vitro?
Low pH is known to induce preferential growth of the yeast form as well as many ‘non-stressful’ conditions.
What factors cause C. albicans to grow in the hyphal form in vitro?
- High pH
- starvation
- Presence of serum
- Presence of N-acetylglucosamine
- Physiological temperature
- Presence of carbon dioxide
What is the term given to the transitioning ability of C. albicans between its yeast and hyphal forms?
Dimorphism
What are the benefits to the C. albican of the hyphal form?
Increased invasion of host cells
Which form is associated with dissemination
The yeast form
Why is the hyphal form of C. albicans more invasive?
Increased expression and presence of adhesin molecules associated with C. albican attachment to the host cell.
Additionaly entry mechanisms
Name a few adhesin molecules associated with the hyphal form of C. albicans.
Als3, Hwp1
What does C. albican bind to via adhesin molecules
Mainly important for attachment to host cells, but also attach to other C. albican cells, other microorganism cells and abiotic structures.
Name other adhesins not asssociated with either form of C. albicans specifically and mention their host cell ligands.
- Glucan -> Vitronectin
- Chitin -> Unknown
- Mannan structures - Macrophage mannose receptor
How does C. albicans enter host cells upon attachment?
Endocytosis thought to be by clathrin dependent mechanism
or
Active penetration
What is required for endocytosis of C. albicans to occur?
Invasins that mediate binding to host ligands to trigger the engulfment of fungal cells
Give an example of an invasin and its host cell ligand binding partner.
Als3
Ssa1
Both bind to E-Cadherin
What is the consequence of mutation of these two invasins?
Reduced attachment and entry into host cells and reduced virulence of infection.
What is required for C. albicans to enter the host cell via active penetration?
The hyphal form.
+Secreion of aspartic proteases is thought to also contribute to invasion.
What is the purpose of biofilm formation?
Biofilms are more resistant to antimicrobial agents and host immune response
What 5 stages are associated with biofilm formation?
- Adherance of yeast
- Proliferation of yeast cells
- Formation of hyphal cells in the upper part of the biofilm
- Accumulation of extracellular matrix material
- Dispersion of yeast cells from biofilm complex
