Week 11: Microbiology

Another 5 weeks passed and it's my turn to post again. Anyway, 5 weeks gone by and I'm shifted to another lab. Fungus lab. A little F.Y.I: In Singapore, the lab must have a special license to operate a fungus lab. Also, fungus cultivation is also a slow process (with incubation time of at least 2 weeks), with low profits and high risks. So many labs may not have a fungus lab, preferring to send their specimens out to a lab with a fungus lab.

Cultivation of fungus is like, as my mentor says, maintaining a garden. Fungi are pretty interesting to look at under the microscope. Instead of the normal GNB and GPC, we can see beautiful formations of conidia and hyphae shaped like flowers.



As different fungi has different morphology, it is possible to observe the fungi under the microscope, note the formation of conidia and hyphae, then identify what type of fungi it is. So unlike bacteria identification, very little biochemical tests are carried out.

Filamentous fungi (moulds) can be differentiated by observing:
- Colour of the mould
- Formation of the spores
- Growth rate
- Temperature differences - some mould grow better at higher temperatures, while others may
grow better at lower temperatures.

Candida spp. are another type of fungi known as yeasts. There are 2 strains that can be differentiated from the other strains. They are Candida albicans and Candida dubliniensis. These 2 strains can be differentiated from the other strains using these 3 tests:
- Germ tube test
- Use of cornmeal agar
- Urea test

Germ tube test: Candida albicans and Candida dubliniensis will produce germ tubes when inoculated into horse serum. These tubes supposedly contributes to the pathogenecity of the organism



The long tubes at the end of cells are germ tubes. (http://upload.wikimedia.org/wikipedia/commons/1/12/C_albicans_germ_tubes.jpg)

Cornmeal agar: It is a medium made up of cornmeal and agar with added Tween 80. After inoculating the organism on the agar, incubate the agar for 18 - 24 hours. Then observe under microscope. These following features should be noted:
-Pseudohyphae
- Blastoconidia
- Chlamydospores

Candida albicans and Candida dubliniensis will have these 3 features while the other Candida spp. will not have chlamydospores. Chlamydospores are lollipop-like cells.


Chlamydospores (http://www.forestresearch.gov.uk/website/FCPicLib.nsf/LUImagesByFilename/43887.jpg/$FILE/43887.jpg)

Urea test: It is basically the same as the one used for bacterial identification. Candida albicans and Candida dubliniensis are urease positive while the other Candida spp. are urease negative. Positive test = pink agar.

To differentiate between Candida albicans and Candida dubliniensis: use API method.

To differentiate the other Candida spp.: use API method.


The medium and agar used in the fungus lab are also different. Instead of the conventional blood agar and macConkey agar, other types of agar are used. I have summarised their abbreviations, functions into the table below. Hope it helps make understanding better.


* Click on picture for bigger view. Sorry for inconvenience =).

So, this is the end of my stint at the fungus lab. Next week, it'll be to the anaerobic lab, where i'll be using this interesting-looking incubator thing.

Hope my post have been coherent enough for understanding!

11th week gone. 9 more weeks to go =).

-Li Ping-
TG o2