Riddell Method- Slide Culture Preparation for Fungal Identification

In order to accurately identify many fungi specifically molds, it is essential to observe the precise arrangement of the conidiophores and the way in which spores are produced. Riddell’s simple method of slide culturing permits fungi to be studied virtually in situ with as little disturbance as possible because many fungi form very fragile reproductive structures which are at least partially disrupted by even the most careful manipulation.

Agars To Be Used

One plate of nutrient agar; potato dextrose is recommended, however, some fastidious fungi may require harsher media to induce sporulation like Cornmeal agar or Czapek Dox agar. Sabourauds Destrose Agar (SAB) may also be used.

Procedure

1. Using a sterile blade cut out an agar block (7 x 7 mm) small enough to fit under a coverslip.
2. Flip the block up onto the surface of the agar plate.
3. Inoculate the four sides of the agar block with spores or mycelial fragments of the fungus to be grown.
4. Place a flamed coverslip centrally upon the agar block.
5. Incubate the plate at 26 degree Celcius until growth and sporulation have occurred.
6. Remove the coverslip from the agar block. Note: Removing the cover slip must be done carefully to keep the reproductive structures intact.
7. Gently lower the coverslip onto a small drop of Lactophenol cotton blue on a clean glass slide.
8. Examine under the microscope

Simple agar block method, inoculated on four sides with cover slip on top. Make at least 2 slides per culture.

Note:

• The slide can be left overnight to dry and later sealed with fingernail polish.
• When sealing with nail polish use a coat of clear polish followed by one coat of red-colored polish.