CULTIVATION OF FUNGI
Most of the fungi grow aerobically on the usual culture media at temperature ranging
from 20-30°C.
Fungi grow slowly than bacteria.
Acidic bacteria that incorporate a relatively high concentration of sugar are tolerated by
molds but are inhibitory to many bacteria. Each fungus has its own specific
requirements which may be known experimentally. Most fungi are able to synthesize
the vitamins they need. However, several fungi may need thiamine or biotin or both
these substances are generally added to synthetic media.
When fungi are cultured in the laboratory on synthetic media, the necessary elements
may be supplied in the following way: C is usually supplied in the form of a
carbohydrate, such as glucose or maltose sucrose and soluble starch are utilized by
many fungi also. N may be supplied in the form of NH4 salt or as amino acids. Many
fungi can utilize NO3 salts.
Some well known media used for cultivation of fungi are:
1) Czapek’s Agar(CZA):
Czapek medium,also called czapek’s agar (cza) or czapek-dox medium for
propagating fungi and other organisms in a laboratory.
It is recommended for use in qualitative procedures for the cultivation of
saprophytic fungi, soil bacteria,and other microorganisms.
The medium was originally developed by czapek in 1902 for the cultivation of
saprophytic fungi. Czapek-dox agar is a modification of the czapek (1902-
1903) and dox (1910) formula prepared accordingly to them and church.
The medium contains sucrose as the sole source of carbon and nitrate as
the only inorganic source of nitrogen.
Composition of Czapek’s Agar- Sucrose, Sodium nitrate, Dibasic potassium
phosphate, Magnesium sulphate, Potassium chloride, Ferrous sulphate, Agar.
Principle of Czapek’s Agar- Czapek medium is a solid, neutral, chemically
defined medium containing sodium nitrate as the sole source of nitrogen.
Fungi and bacteria capable of utilizing this inorganic nitrogen source will
grow.
Sucrose is an energy source and the sole source of carbon.
Dibasic potassium phosphate is a buffering agent, potassium chloride
contains essential ions, and magnesium sulphate and ferrous sulphate are
source of cations.
Example-Aspergillus brasiliensis, Candida albicans, Aspergillus niger, Saccharomyces
cerevisiae, etc
2) Potato Dextrose Agar (PDA):
Potato Dextrose Agar (PDA) is used for the cultivation of Fungi. PDA is a
general purpose medium for yeasts and molds that can be supplemented
with acids or antibiotics to inhibit bacterial growth.
The nutritionally rich potato (base) encourages mold sporulation and
pigment production in some Dermatophytes.
Principle- PDA is composed of dehydrated potato infusion and dextrose that
encourage luxuriant fungal growth. Agar is added as the solidifying agent.
The pH is kept lower (around 3.5) with 10% of Tartaric acid to prevent
bacterial growth.
Composition of PDA- Potato infusion, Dextrose, Agar, Distilled water.
Uses- PDA is used to detect yeasts or molds in dairy products and prepared
food.
-Used for cultivation of yeasts and molds from clinical specimens.
-PDA with Chloramphenicol is recommended for the selective cultivation of
fungi from mixed samples.
Example-Aspergillus flavus(powdery masses of yellow –green spores), Penicillium
chrysogenum(Olivaceous green with sterile white margin), etc.
3) Sabouraud Dextrose Agar (SAD):
Sabouraud Dextrose Agar (SDA) is used for the isolation, cultivation, and
maintenance of non-pathogenic and pathogenic species of fungi and yeasts.
SDA was formulated by Sabouraud in 1892 for culturing dermatophytes.
The pH is adjusted to approximately 5.6 in order to enhance the growth of
fungi, especially dermatophytes , and to slightly inhibit bacterial growth in
clinical specimens.
Yeasts will grow as creamy to white colonies (at 28° to 30° C temp.) while
molds will grow as filamentous colonies of various colours (at 22° to 25° C
temp.
Principle: Peptone provides the nitrogen and vitamin source required for
organism growth in SDA. Dextrose is added as the energy and carbon source.
Agar is the solidifying agent.
Chloramphenicol and/or tetracycline may be added as broad spectru m
antimicrobials to inhibit the growth of a wide range of gram-positive and
gram-negative bacteria.
Gentamycin is added to further inhibit the growth of gram-negative bacteria.
Composition of SDA:Dextrose, Peptone, Agar, Distilled water.
Uses: -SDA is primarily used for the selective cultivation of yeasts, molds and
aciduric bacteria.
The medium is often used with antibiotics for the isolation of pathogenic
fungi from material containing large number of other fungi or bacteria.
This medium is also employed to determine microbial contamination in food,
cosmetics and clinical specimens.
Limitations of SDA: -Some strains may be encountered that grow poorly or
fail to grow on this medium.
Antimicrobial agents added into a medium to inhibit bacteria may also inhibit
certain pathogenic fungi.
It does not promote conidiation of filamentous fungi.
Examples: Penicillium glabrum, Sporothrix skenckii, Candida albicans, Trichophyton
terrestre, etc.
