Fungi and Medicine Flashcards
Insert the correct species names in the blank spaces of these statements.
- Its conidia of can infect the lungs of immuno-suppressed individuals.
- A commensal organism that can change its growth mode to become an invasive pathogen in susceptible hosts
- Is present in soil and bird excreta and can cause meningitis in persons.
- Changes in pH around the mucosal membranes can affect its pathogenicity
- The presence of a polysaccharide capsule, the ability to grow at 37° Celsius and in high levels of CO2 are important features that affect its pathogenicity
A. Cryptococcus neoformans
B.Aspergillus fumigatus
C.Candida albicans
- B Aspergillus
- C Candida albicans
- A Cryptococcus
- C Candida albicans
- A Cryptococcus
(1) Conidia is the clue that determines Aspergillus fumigatus as it is basidiospores of Cryptococcus neoformans that enter the body. (2) Candida albicans is normally a harmless commensal organism but changes from yeast growth to hyphal growth when it becomes invasive. (3) Cryptococcus neoformans typically spreads through the bloodstream as yeast cells and causes meningitis when it colonises the brain. (4) Candida albicans tends to grow as yeast in slightly acidic environment, however it can switch to invasive hyphal growth when the pH changes to neutral or alkaline, often as a result of loss of commensal lactic acid bacteria following treatment with antibiotics. (5) The polysaccharide capsule helps this pathogen to evade the host’s immune system, together with the ability to grow at body temperature
What are the known effects of ingesting the following fungal secondary metabolites / mycotoxins?
Aflatoxin
α-Amanitin
Coprine
Ergotamine
Muscarine
Orellanin
Psilocybin
A. Hallucinations, paranoia, euphoria
B. Hallucinations, gangrene
C. Nausea, sweating, blurred vision, salivation, bradycardia
D. Liver cancer
E. Nausea, vomiting, headaches
F. Vomiting followed by liver failure
G. Kidney failure
Aflatoxin- D (liver cancer)
α-Amanitin - F (vomitting then liver cancer)
Coprine- E (Nausea, vomitting, headaches)
Ergotamine- B (Hallucinations, gangrene)
Muscarine- C (Nausea, sweating blurred vision, salivation, bradycardia)
Orellanin- G (Kidney failure)
Psilocybin- A (Hallucinations, paranoia, euphoria)
Aflatoxin, produced by some Aspergillus moulds is a known carcinogen, and is likely to accumulate after repeated exposure. Amanitin produced by the Death Cap causes irreversible liver damage, and is often fatal. Coprine only causes ill effects when combined with alcohol, and its action resembles that of the drug antabuse used to treat alcoholics. The ergot fungus contains a cocktail of alkaloids including ergotamine, that may cause both psychoactive effects and constriction of blood vessels resulting in gangrene. Muscarine is produced by several types of toxic mushrooms e.g. Clitocybe and causes profound activation of the peripheral parasympathetic nervous system; atropine is used as an antidote due to its anti-muscarinic action. Orellanin produced by Cortinarius species acts on proximal tubules resulting in kidney failure, usually requiring organ transplant. Psilocybin is an alkaloid that resembles serotonin and may produce visual and auditory hallucinations, and is currently under clinical investigation as a treatment for depression.
TRUE or FALSE?
-Aspergillus fumigatus is highly contagious to persons in close contact with infected patients.
-On average we breathe in 100-200 fungal spores per day.
-The ergot fungus (Claviceps purpurea) can cause skin and nail infections.
-Candida albicans can spread systemically via the blood vessels as yeast cells.
-Cryptococcus neoformans can spread from the lungs to the central nervous system as yeast cells.
-Penicillin, discovered by Alexander Fleming, was the first antifungal drug to be used worldwide.
- False
- True
- False
- True
- True
- False
Aspergillus fumigatus cannot be directly transmitted from person to person and is restricted to immunodeficient persons.
We breathe in hundreds of spores each day and in healthy individuals they are removed by secretions or phagocytised.
The ergot fungus is a mycotoxin producing pathogen of rye grass but does not infect humans.
Once it has penetrated the epithelial tissues, Candida albicans reverts to the yeast form where it can spread through the bloodstream to cause systemic infections.
The primary source of Cryptococcus neoformans is from the outdoor environment and it is not transmitted from host to host.
Penicillin is an antibacterial drug, not an antifungal.
Match the type of antifungal with it’s mode of action.
Fluconazole
5-Flucytosine
Caspofungin
Amphotericin B
A. Inhibits DNA and protein synthesis
B. Forms pores in the plasma membrane
C. Inhibits β(1-3)-glucan synthesis
D. Inhibits ergosterol synthesis
Fluconazole - D. Inhibits ergosterol synthesis
5-Flucytosine- A. Inhibits DNA and protein synthesis
Caspofungin - C. Inhibits β(1-3)-glucan synthesis
Amphotericin B- B. Forms pores in the plasma membrane
Fluconazole is an azole antifungal which inhibits synthesis of ergosterol, an important component of the fungal plasma membrane.
5-Flucytosine inhibits the enzyme thymidylate synthase preventing DNA synthesis and 5-fluorouracil, a product of 5-Flucytosine becomes incorporated into RNA preventing protein synthesis.
Caspofungin inhibits glucan synthase resulting in depletion of (1-3)-glucan and weakened cell walls.
Amphotericin B associates with ergosterol, forming pores in the plasma membrane resulting in leakage of intracellular ions and proteins
What is Cryptococcuus neoformans?
- grows in lungs of immunocomprimised people and infect CNS causing meningitis
- spread through bird droppings
- can grow in 5% CO2 and at 37˚
- Thick capsule
- Melanin
What is Aspergillus fumigatus?
- found normally as sarotrophs, but grows in lungs of immunocomprimised people
- grows in compost heaps and can grow at 37˚
- On average we breath in 100-200 Aspergillus conidia per day
What is Candida albicans?
- Commensal that can become pathogenic under right conditions
- Grows on mucus membranes
- Penetrates epithelial cells and gets into bloodstream as yeast cells
Whats the term for mold/fungi that infect humans?
Mycoses
What are the three mycoses of humans and examples of each?
- Dermatophytes (Trichophyton)
- Commensals (Candida albicans)
- Opportunistic pathogens of the lungs (Aspergillus fumigatus, Cryptococcus neoformans)
What are characteristics of opportunistic pathogens? (Fungi)
- caused by fungi that grow as saprotrophs in soil or plant / animal remains
- Establish infections in the lungs from spores
- Do not spread by host-to-host transmission
- Infections mostly restricted to immunodeficient hosts
Opportunistic pathogens are potentially ANY fungus that:
(a) produces spores small enough that can reach alveoli (<4µm)
(b) can grow at 37oC
(c) can withstand / evade host defences
What are the function and example of each of the following anti-fungal drugs:
- Azoles
- Polyene antibiotics
- Echinocandins
- Flucytosine
Azoles: inhibit ergosterol, treats Candida albicans & athletes foot (eg Fluconazole, Ketoconazole)
Polyene: forms pores in plasma membrane to fuck with ion homeostasis ( eg amphotericin B, nystatin)
Echinocandins: Inhibit synthesis of β(1,3)-glucan (eg. caspofungin)
Flucytosine: inhibit DNA/protein synthesis (eg 5-fluorocytosine)
ergosterol is an important component of the fungal plasma membrane
