Description

Sabouraud Dextrose Agar (SDA) serves as a specialized culture medium, primarily designed for the isolation and cultivation of fungi, including yeasts and molds. Originally formulated by Raymond Sabouraud in 1892, it remains a vital tool in various laboratory settings, such as clinical, pharmaceutical, food, cosmetic, and environmental laboratories. Its primary function is to detect and enumerate fungal contamination, making it indispensable for research and laboratory diagnosis of fungal infections.

Key Features

• Acidic pH: Typically ranging from 5.4 to 5.8, the acidic environment inhibits most bacterial growth while promoting fungal growth. This characteristic can be further enhanced by supplementing the medium with antibiotics like chloramphenicol, gentamicin, or tetracycline to suppress bacterial contamination.
• Versatility: Supports the growth of a wide range of fungi, including dermatophytes, Candida, Aspergillus, and some filamentous bacteria such as Nocardia spp.
• Modifications: Available in various forms, including the Emmons version, with different dextrose levels and pH to support specific fungal growth or differential identification.

Standard Composition

For every liter, the medium typically includes:

• 40 g of dextrose (glucose)
• 10 g of mycological peptone
• 15 g of agar
• 1000 mL of distilled water

The final pH is adjusted to 5.6 ± 0.2 at 25°C.

Preparation Guidelines

1. Suspend the dry medium in distilled water (approximately 65 g/L).
2. Heat to dissolve completely and adjust the pH.
3. Autoclave at 121°C for 15 minutes.
4. Cool to 45–50°C and, if necessary, add filter-sterilized antibiotics aseptically.
5. Pour into sterile Petri dishes or tubes and store at 4°C until use.

Colony Morphology

• Yeasts: Typically form creamy to white, smooth colonies.
• Molds: Exhibit filamentous colonies with variable color and texture, depending on the species.

Quality Control

• Dehydrated Medium: Appears as a straw-colored powder.
• Prepared Medium: Forms a pale straw to straw-colored, slightly opaque gel.

Variants and Modifications

• SDA with Chloramphenicol
• SDA with Chloramphenicol and Gentamicin
• SDA with Chloramphenicol and Tetracycline
• Emmons modification with altered dextrose and pH levels

Limitations

• Some fungi may exhibit poor growth or be inhibited by added antibiotics.
• Not all bacteria are inhibited by the acidic pH.
• Overheating during preparation can damage the medium.
• Further tests are required for definitive identification of isolates.

Sabouraud Dextrose Agar is also known as Sabouraud Glucose Agar or Sabouraud Agar. It is often used alongside other media for comprehensive fungal detection, with typical incubation at 20–25°C for up to five days.