Elementary Mycology - Answers

Arlo Guthrie — Mon, 20 Apr 2009 13:52:12 GMT

Current Revision posted to Revision Guide For Student Nurses - Part 2 by Arlo Guthrie on 4/20/2009 1:52:12 PM

ANSWERS

What are the 2 main groups of fungi?
- Yeasts.
- Moulds.
Give 2 examples of yeasts.
- Candida albicans - often present in the intestinal tract without causing disease, but may become pathogenic if the host's resistance is lowered.
- Malassezia pachydermatitis - a yeast found on normal skin, but may cause dermatitis.
How do yeasts reproduce?
Asexually by budding.
What is the main difference between yeasts and moulds?
Yeasts are unicellular and usually round or ovoid, whilst moulds are multicellular and composed of long filaments called hyphae.
What is the main similarity between yeasts and moulds?
They both grow aerobically and derive their nutrition from the organic substances upon which they grow.
How do moulds reproduce?
Either asexually, or sexually by spore production.
What is the name of the saprophytic fungus which produces the toxin aflatoxin?
Aspergillus flavus.
What is the name given to a fungus that invades keratin (the horny tissue that forms nails, skin and hair)?
A dermatophyte.
Name the 3 genera of dermatophyte responsible for ringworm.
- Epidermophyton.
- Microsporum.
- Trichophyton.
Of the genera listed in your answer to Q9, which is most likely to fluoresce under a Wood's lamp?
Microsporum canis (lesions may appear apple green, but remember that not all strains fluoresce and therefore a negative Wood's test does not rule out fungal infection.
What type of light is emitted by the Wood's lamp?
Ultraviolet.
How long should the Wood's lamp be warmed up for prior to use?
5-10 minutes.
In addition to the use of the Wood's lamp, list other laboratory techniques used in the diagnosis of ringworm.
- Microscopic examination of skin and hair - the sample is mounted in 10% potassium hydroxide and may be stained with Lactophenol or Indian ink in order to improve visualisation.
- Culture on a specialist medium - proprietary media include Sabouraud's agar or Dermafyte tests; the latter contain a colour indicator that changes from yellow to red in the presence of dermaphytes.
List 4 topical treatments used to treat ringworm.
- Fungicidal wash containing enilconazole.
- Povidone iodine.
- Chlorhexidine wash.
- Fungicidal creams such as Canestan.
What is the name of the systemic drug used in the treatment of ringworm?
Griseofulvin (Fulcin).
Describe the McKenzie brush technique.
This is used in dermatophyte investigation and is used to identify asymptomatic carriers. The animal is brushed all over with a sterile toothbrush (particular attention must be paid to the feet and face). The toothbrush is then sent directly to the laboratory for analysis or inoculated into culture medium.