Question

3. List two types of media for growing fungi.

Answer 1

Sabouraud’s agar

Sabouraud’s agar is sufficient for the recovery of dermatophytes from cutaneous samples and yeasts from genital cultures.

Typical composition. Sabouraud agar is commercially available and typically contains: 40 g/L dextrose. 10 g/L peptone. 20 g/L agar. pH 5.6.

Sabouraud’s dextrose agar (2%) is most useful as a medium for the subculture of fungi recovered on enriched medium to enhance typical sporulation and provide the more characteristic colony morphology.Sabouraud Dextrose Agar (SDA) is a selective medium primarily used for the isolation of dermatophytes. Other fungi, yeasts, and filamentous bacteria such as Nocardia can also grow in SDA. The acidic pH of this medium (pH about 5.0) inhibits the growth of bacteria but permits the growth of yeasts and most filamentous fungi. Antibacterial agents can also be added to augment the antibacterial effect.This medium is also employed to determine the mycological evaluation of food, contamination in cosmetics, and clinically to aid in the diagnosis of yeast and fungal infections.

Antibiotics like chloramphenicol, gentamicin, and tetracycline can be added as selective agents to inhibit the bacterial overgrowth of competing microorganisms while permitting the successful isolation of fungi and yeasts. Various other modifications are also reported by using cycloheximide, penicillin, streptomycin, neomycin depending upon the intended use.

Potato Dextrose Agar (PDA)

Potato Dextrose Agar (PDA) is used for the cultivation of fungi. Potato Dextrose Agar (PDA) is a general purpose medium for yeasts and molds that can be supplemented with acid or antibiotics to inhibit bacterial growth. It is recommended for plate count methods for foods, dairy products and testing cosmetics. PDA can be used for growing clinically significant yeast and molds. The nutritionally rich base (potato infusion) encourages mold sporulation and pigment production in some dermatophytes.

Potato Dextrose Agar is composed of dehydrated Potato Infusion and Dextrose that encourage luxuriant fungal growth. Agar is added as the solidifying agent. Many standard procedures use a specified amount of sterile tartaric acid (10%) to lower the pH of this medium to 3.5 +/- 0.1, inhibiting bacterial growth. Chloramphenicol acts as a selective agent to inhibit bacterial overgrowth of competing microorganisms from mixed specimens, while permitting the selective isolation of fungi.