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BFI: Biology > Fungi, Fungal + Anti-fungal infections > Flashcards

Fungi, Fungal + Anti-fungal infections Flashcards

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1
Q

Key structural differences between fungi + human cells

A
  • Rigid wall = made from Chitan (or glucan + mannan)
  • cytoplasmic membrane contains Ergosterol
    But both eukaryotic cells
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2
Q

Examples of fungi

A

Moulds, yeast + mushrooms

  • penicilium
  • aspergillus
  • saccharomyces
  • candida
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3
Q

What are fungi an example of

A

Heterotrophic (saprotrophy, symbiosis + parasitism)

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4
Q

How many phyla do they have?

A

4

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5
Q

Name the phyla

A

Ascomycota, basidiomycota, zygomycota, chytridiomycota

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6
Q

2 variable fungal morphologies

A

Hyphae - network of filaments e.g. moulds + mushrooms

Single celled budding organisms e.g. yeasts

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7
Q

What fungi can convert from the fungal morphologies

A

Dimorphic fungi can convert between hyphae + yeast depending on temperature

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8
Q

Sporulation

A

spores allow fungi to spread, maintain genetic diversity + survive adverse conditions
Spores are airborne - which contribute to allergies + specific, life-threatening conditions (histoplasmosis/coccidiomycosis)

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9
Q

What causes fungal infections?

A
  • overgrowth of natural flora
  • inhalation of fungal spores
  • traumatic implantation
  • primary/secondary to other conditions (HIV/immunocompromised)
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10
Q

What are the fungal pathogenicity factors?

A
  • adhesion to host cells
  • capsules to prevent phagocytosis
  • secrete various biochemical factors to help tissue invasion/spread + suppress immune response
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11
Q

What are infections classified by?

A

Location + opportunism

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12
Q

5 classifications

A 
Superficial
Subcutaneous
Cutaneous
Systemic
Opportunistic
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13
Q

Example of superficial

A

Piedras

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14
Q

Example of cutaneous

A

Tineas

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15
Q

Example of subcutaneous

A

Mycetoma, chromablastomycosis, sporotrichosis

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16
Q

Example of systemic

A

Blastomycosis
Cryptococcal meningitis
Histoplasmosis
Coccidiomycosis

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17
Q

Example of opportunistic

A

Candidosis, aspergillosis

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18
Q

What do opportunistic pathogens cause?

A

Localised mucosal/ systemic infections

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19
Q

Who are susceptible to opportunistic fungal infections?

A

Immunocompromised patients (aid/hiv, elderly, infants, transplant patients - as immune system is suppressed)

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20
Q

Examples of poisoning - fungal infections

A

Ergot in wheat
Aflatoxin in peanuts
Mushrooms/toadstools

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21
Q

What are poisoning - fungal toxins called?

A

Mycotoxins

22
Q

What is mycoses?

A

Fungal infection

23
Q

Superficial mycoses

A

Harmless - cosmetic ‘blemishes’
Cause minimal destructive disease
Rarely induces an immune response

24
Q

Treatment for Superficial mycoses

A

Selenium-based shampoo
Nizoral body wash
Topical antifungals
Good personal hygiene

25
Q

Cutaneous mycoses

A

Dermatophyte fungi that eat keratin protein in hair, nails and skin
Cause chronic conditions cause Tineas
Can start inflammatory reactions from host
Contagious
Respond well to topical agents
Systemic therapy required for extensive infection

26
Q

Name the different Tineas

A

Tinea capitis - infection of hair + scalp
Tinea corporis - ringworm of trunk, legs + arms
Tinea pedis athletes foot
Tinea cruris - jock itch (genital region)
Tinea urguium - onychomycosis, nail infection

27
Q

Subcutaneous mycoses

A

Infection arises after fungi is introduced by trauma, small wounds, splinters, thorns,
Infects skin + underlying tissues
May require amputation or surgical excision

28
Q

Systemic mycoses

A

Opportunistic pathogens e.g. immunocompromised patients
Caused by spore inhalation (lungs) e.g. Histoplasmosis, coccidioidosis, aspergillosis, blastomycosis
or spread from mucosal infections e.g. Candidiosis
Lung: pneumonia or flu-like symptoms, followed by spread to other organs, systemic infection
Rapid diagnosis + aggressive therapy
Caused by dimorphic fungi

29
Q

Outline the opportunistic mycoses

A

Candida albicans
Aspergillus fumigatus
Cryptococcus neoformans
Pneumocystis spp.

30
Q

Candida Albicans

A

Component of mucosal + cutaneous microflora
Oral thrush + antibiotic use/immunocompromised
Vaginal thrush (common in women)
Candidiosis (common in diabetes, cancer, HIV, burns patients)
Systemic infection linked with immunocompromised patients with catheters, burns or post surgery
Dimorphic - linked to pathogenicity

31
Q

Aspergillus fumigatus

A

Cause of pulmonary aspergillosis (asthma, cystic fibrosis)
Found in wet soil, damp surfaces
Caused by spore inhalation (route of infection)
Causes allergic reactions in asthma + CF patients
Release toxins, phospholipases, haemolysins + facilitate spread to other tissues

32
Q

Pneumocystis spp.

A

Environmental fungus
Inhaled spores affect patients with aids + premature infants
Pneumonia

33
Q

Cryptococcus neoformans

A 
Found in soil contaminated with bird droppings 
Cause by spore inhalation 
Affects immunocompromised patients
Cause of meningitis in AIDS patients
Surrounded by a capsule
phagocytosed by macrophages
Survives + multiplies within macrophage
34
Q

Classes of antifungals used to treat fungal infections

A

Polyenes
Azoles
Nucleoside
Echinocandins

35
Q

What do Azoles target?

A

Ergosterol synthesis

  • bind to fungal p450 enzyme
  • cell membrane stability disrupted
36
Q

What do Polyenes target?

A

Cell membrane

  • bind to ergosterol in cell membrane
  • causes cell leakage
  • renal toxicity (side effect)
37
Q

What do Nucleoside derivatives target?

A

DNA/RNA synthesis

- selective uptake / metabolic activation in fungal cell

38
Q

What do Echinocandins target?

A

Cell wall synthesis

  • blocks B1-3 glucan polymer synthesis
  • destabilises cell wall
39
Q

Polyene examples

A

Amphotericin B - fungicidal
They can damage fungi better than mammalian cells as they prefer ergosterol-containing membranes

Low dose = leakage of essential ions from cytosol
High dose = cell destruction

Intravenous injection
Poor selectivity; lipid complex or liposome may help

40
Q

Azole examples

A

Imidazoles + Triazoles - largest group of antifungals (fungistatic)
Inhibit 14a - demethylation of 24 methyledihyydrolanosterol (ergosterol precursor)
Leads to
- depletion of ergosterol
- accumulation of 14a-methylated sterols resulting in growth arrest

Reaction dependent upon cytochrome p450; azoles bind haem component of cytochrome p450

Not entirely selective - interferes with mammalian sterol metabolism (testosterone)

41
Q

Nucleoside examples

A

Flucytosine

Used orally to treat systemic infections

42
Q

Mode of action of nucleosides

A

Taken up by cytosine permease
Rapidly deaminated to 5-fluorouracil (gives fungal selectivity)
Converted to 5-fluorouridylic acid monophosphate (FUMP, inhibits RNA function) or 5-fluorodeoxyuridine monophosphate (inhibits DNA synthesis)

43
Q

Other treatment for fungal infections

A

Grisans
Allylamines
Morpholines

44
Q

Resistance in antifungals

A

Exposure to fungal pathogens to antifungals

45
Q

Enchinocandins examples

A

Capsofungin
Micafungin
Anidulafungin

46
Q

Resistance mechanism to polyenes

A

Lower production of membrane sterols
Altered sterols bind drug with lower affinity
Reorientation/masking existing ergosterol

47
Q

Resistance mechanism to Nucleosides

A

Decreased uptake
Loss of enzymatic activity
Resistance develops rapidly (with other antifungals it is fine)

48
Q

Resistance mechanism to enchinocandins

A

Resistance to glucan synthesis

49
Q

Resistance mechanism to azoles

A

Increase target enzyme by gene amplification / upregulation of encoding gene
Mutations in lanosterol demethylase enzyme
Active efflux

50
Q

Other resistant mechanism

A

Formation of biofilms

- poor pentration of antifungals into biofilms + efflux pumps are upregulated

BFI: Biology (9 decks)

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