Fungal infections in dentistry

Question 1

Know the characteristics of (what defines) a fungus

Answer 1

• Eukaryotic (cells that have a nucleus enclosed within a nuclear envelope and contain other organelles)
• Lack chlorophyll (they do not photosynthesize)
• Multicellular (hyphae) and unicellular (yeast)
• Non- motile
• Absorptive nutrition (osmotrophy)
• Reproduce both sexually and asexually
• Spore forming
• Most are saprophytes (decomposers)

Question 2

List the 4 morphological of fungi

Answer 2

Yeast

Pseudo-hypahae

Hyphae

Mating projection

Question 3

Describe the 4 morphological of fungi

Answer 3

Yeast:
• Small, circular, ovoid shape
• When growing, they bud off from the mother cell

Pseudo-hypahae:
• Cells are elongated
• When growing, they bud off from the mother cell and may form cells stuck in a chain

Hyphae:
• Grow a projection that are long and use this to penetrate into the food source and obtain nutrients

Mating projection:
• Small projections that touch other cells, and in that projection the have their genetic material which is passed on to the receiving cell

Question 4

Describe the yeast cell membrane

Answer 4

• They have a typical lipid bilayer
• They do not have peptidoglycan like bacteria
• They have a cell wall above the lipid bilayer made of glucan and mannan products
• Their inner wall, which is made of glucans, is proinflammatory. The immune system recognises the B glucan products of the inner wall of the yeast. This stimulates monocytes to turn into dendritic cells and activate the inflammatory mediators
• Their otter wall consists of mannan which isn’t as proinflammatory
• Hyphae have their inner wall exposed (they loss the outer wall)

Question 5

List 6 mechanisms of pathogenicity of fungal organisms

Answer 5

1. Yeast to hyphal transition
2. Epithelial invasion
3. Escape phagocytosis
4. Complement inhibition
5. Inhibit phagolysosome
   fusion
6. Modulate T cell function

Question 6

Describe the 6 mechanisms of pathogenicity of fungal organisms:
1. Yeast to hyphal transition

2. Epithelial invasion
3. Escape phagocytosis
4. Complement inhibition
5. Inhibit phagolysosome fusion
6. Modulate T cell function

Answer 6

1. Yeast to hyphal transition:
   • C. albicans is a dimorphic fungus
   • The morphological switch between the yeast phase and the hyphal phase is considered to be the main virulence factor of C. Albicans
   • Transcription of genes is what enables the switch
   • These transcriptional factors are activated by different environmental stimuli.
2. Epithelial invasion
   • Once C. albicans is inside the epithelial cells, it forms hyphae, leading to piercing of the cells
3. Escape phagocytosis
   • To phagocytose Candida species, the host cells first need to “sense” the microorganism through PAMPs of Candida
   • It has been shown that B - glucan is shielded by the outer cell wall components, thus preventing the recognition
4. Complement inhibition
   • Complement factors normally punch holes in the cell membrane of fungal cells and kill it
   • Some fungi may have proteins on their cell wall that recruit complement regulators which stop the complement cascade, enabling them to live
5. Inhibit phagolysosome fusion
   • They can prevent lysosome and phagosome fusion, which would otherwise enable destruction of the intracellular pathogen
6. Modulate T cell function:
   • Prevent production of cytokines like IFN- y in the host which are essential for T cell function and recruitment
   • The down regulation of IFN-y leads to upregulation of IL- 10, shifting the T helper cell response from a beneficial Th1 response to a detrimental Th2 response

Question 7

List some oral fungal species

Answer 7

• Candida spp. eg. Candida albicans, Candida glabratta
• Aspergillus spp
• Cryptococcus neoformans
• Histoplasma capsulatum
• Saccharomyces spp
• Mucor spp
• Geotrichum spp

Question 8

Understand the clinical presentation of primary oral candidiasis (3) and candida- associated lesions (4)

Answer 8

Clinical presentation of primary oral candidiasis:
• Pseudomembranous candidiasis or “thrush”
• Erythematous candidiasis
• Hyperplastic candidiasis

Candida-associated lesions: 
• Denture stomatitis 		
• Angular cheilitis 		
• Median rhomboid glossitis 		
• Linear gingival erythema

Question 9

Know the 9 predisposing factors to oral candidiasis

Answer 9

• Physiological: very young, old age, pregnancy
• Local trauma: mucosal irritation, poor OH
• Antibiotics: prolonged & broad-spectrum
• Corticosteroids: asthma inhalers, systemic steroids
• Malnutrition: High carb diet, deficiencies in iron, folate, B12
• Endocrine: hypoendocrine states eg. hypothyroidism, Addison’s disease
• Blood disorders: leukemia, agranulocytosis
• Immune deficiencies: HIV, immunosuppressed
• Xerostomia: Sjogren’s syndrome, radiotherapy, drug induced, chemotherapy

Question 10

Understand the course of treatment for candidiasis (2 steps)

Answer 10

Step 1. Antifungals (esp. nystatin, azoles & triazoles) which come in the following forms:
• Lozenges 
• Cream 
• Oral suspensions 
• Systemic (tablets/capsules) 

Step 2. Stop precipitating factors: 
• Stop broad-spectrum antibiotics 
• Treat AIDS 
• Improve oral & denture hygiene 
• Correct denture problems 
• Improve diet if deficient