Practical 1: Medical Mycology Flashcards
Learning about fungi (25 cards)
Why are special fungal cultures order than routine cultures?
this is because routine cultures do not isolate the fungi
What are the types of specimens used for diagnostic purposes?
a) Scraping from the hair, skin, nails
b) Urine
c) Cerebrospinal fluid
d) Blood
e) Bone marrow
f) Swabs: cervical and vaginal swabs
g) Respiratory tract secretions
h) Tissue samples
i) Body fluids such as aspirates and pus
j) Biopsies
What are the requirements for the media used in fungal isolation?
- Media with antibacterial agents, in order to prevent the growth of bacteria
- Media with or without blood enrichment
- Media with or without cycloheximide to inhibit some bacteria and fungi
With the use of cycloheximide, what fungi or bacteria are inhibited?
Mnemonic T-ry A-sparagus P- Paella C- anned C- risps
- Cryptococcus neoformans
- Candida krusei
- Trichosporon cutaneum
- Pseudallescheria boydii
- Aspergillus spp
What are the examples of the medias used?
a) Sabouraud Dextrose Agar (SDA)
b) Mycosel
c) Brain-heart infusion agar (BHIA)
d) Brain-heart infusion with antibiotics (BHIWA)
e) Inhibitory mould agar
f) Potato flake agar
What are the indications for the above mentioned medias?
a) Used for the recovery of saprobic and pathogenic fungi: BHIA, SDA, Potato flake agar,
b) Used for the recovery of dermatophytes: BHIWA, Mycosel and Inhibitory mould agar.
What is the incubation period and investigation for cultures?
They are incubated at room temperature or 30 degrees for 30 days.
Cultures are examined at least 3 times weekly
What are the characteristics of moulds on cultures?
They produce fluffly, woolly, cottony or powdery colonies
Give an example of a mould and in what culture media is it recovered from?
Aspergillus niger, that is grown in Potato dextrose agar, Malt yeast agar and Sabouraud dextrose agar
What are the characteristics of yeasts in cultures?
They produce moist, creamy, opaque or past colonies
Give an example of a yeast and the media it grows in?
Candida albicans/ Candida parapsilosis, it grows on Sabouraus dextrose agar
What are the methods used for direct examination of fungi?
- KOH preparation
- India ink
- Calcofluor white stain
- Lactophenol cotton blue stain
What are the indications for KOH preparation?
a) It partially ingests protein components, to allow the fungal wall to be intact.
b) This examination allows for better viewing of the fungi.
c) Used as the primary screening tool, it is not used to detect the species of the fungi but allows for clear viewing of the fungal elements
What are the indications for India ink?
a) It is used to detect the presence of the yeast Cryptococcus neoformans in cerebrospinal fluid.
What are the indications for calcofluor white stain?
It uses fluorescence, in order to detect fungi
What are the indications for lactophenol cotton blue stain?
a) It is used in combination with potassium hydroxide to enhance the viewing of fungal elements
b) It is a wet mount preparation
What are the components of the lactophenol cotton blue stain?
a) phenol
b) lactic acid
c) cotton blue
What does each components of the LCBS do?
a) Phenol: kills any live organisms
b) Lactic acid: preservation of the fungal structures
c) Cotton Blue: stains the chitin in the fungal cell wall.
What are the other ways in which India ink can be used for the detection of the C. neoformans?
Use of Cryptococcal latex agglutination test to detect the C. neoformans antigen
What is the germ tube test?
A method of identification for yeasts
What are the indications for the germ tube test?
Used as a differentiating and identification tool for Candida albicans from other Candida species
What are the other species of Candida other than albicans?
Mnemonic T- tropical P- paradise K/P- kentucky K- kruising G- Guillets
a) C. tropicalis
b) C. parapsilosis
c) C. kefyr/ pseudotropicalis
d) C. krusei
e) C. guilliermondii
What is a positive germ tube test? What does it indicate?
Short hyphal extension, from the lateral part of the cell, without any constrictions at the point of origin.
This test is positive for C. albicans
What is a negative germ tube test? What does it indicate?
No hyphal extension from the cell or short hyphal extension with constrictions at the point of origin.
This test is indicative of the presence of the other Candida spp other than albicans.
