Sabouraud Dextrose Agar: Principle and Culture characteristics

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Rhodotorula_mucilaginosa_colonies on sabouraud dextrose agar

Sabouraud Dextrose Agar is a culture medium for yeasts, molds, and aciduric microorganisms. Sabouraud Dextrose Agar is Carlier’s modification of Sabouraud’s formulation for the cultivation of fungi (yeasts, molds), which is especially useful for fungi associated with skin infections. This medium is also used to detect microbial contamination in food, cosmetics, and clinical samples.

Principle of Sabouraud Dextrose Agar

  • Nitrogenous compounds are provided by mycological peptone.
  • Dextrose is a source of energy.
  • Fungal growth is aided by a high dextrose concentration and a low pH, while contaminating bacteria from test samples are inhibited.
  • Some pathogenic fungi can produce infective spores that are easily dispersed in the air, so testing should be done in a safety cabinet.
  • In order to inhibit bacterial growth with lower pH, the plate must be supplemented with inhibitory agents for heavily contaminated samples.

Composition of Sabouraud Dextrose Agar

Dextrose40.000
Mycological peptone10.000
Agar15.000
Final pH ( at 25°C)5.6±0.2

Preparation procedure of Sabouraud Dextrose Agar

  • In 1000 mL of purified/distilled water, dissolve 65 grams.
  • To completely dissolve the medium, bring to a boil.
  • Sterilize by autoclaving at 15 pounds of pressure (121 degrees Celsius) for 15 minutes, or according to the validated cycle.

Type of specimen

Pharmaceutical samples, Clinical samples such as Skin scrapings

Quality Control of Sabouraud Dextrose Agar

AppearanceCream to yellow homogeneous free flowing powder
Color and Clarity of prepared mediumLight amber colored clear to slightly opalescent gel forms in Petri plates
pH5.40-5.80
GellingFirm, comparable with 1.5% Agar gel
Uninoculated sabouraud dextrose agar
Uninoculated sabouraud dextrose agar

Cultural Response on Sabouraud Dextrose Agar

Candida albicansLuxuriant (white colonies)30 -35 °C24 -48 hrs
Aspergillus brasiliensisluxuriant20 -25 °C<=5 d
Saccharomyces cerevisiaeluxuriant30 -35 °C24 -48 hrs
Escherichia coligood(inhibited on media with low pH)30 -35 °C24 -48 hrs
Trichophyton rubrumgood20 -25 °C<=5 d
Lactobacillus caseiluxuriant30 -35 °C24 -48 hrs

Storage and Shelf Life

  • Keep the prepared medium at 20-30°C and the prepared medium at 10-30°C in a tightly closed container.
  • Use before the expiration date printed on the label.
  • Due to the hygroscopic nature of the product, the product should be stored dry after opening and tightly capping the bottle to prevent lump formation. Improper product storage may result in the formation of lumps.
  • Store in a dry, ventilated area away from extremes of temperature and ignition sources.
  • After use, tightly close the container.
  • Use before the expiration date printed on the label.
  • When used within the specified expiry period, the product performs best.

Limitations

  • In the case of heavily contaminated samples, the plate must be supplemented with inhibitory agents to inhibit bacterial growth at lower pH.
  • Because some pathogenic fungi can produce infective spores that are easily dispersed in the air, testing should be performed in a safety cabinet.
  • Further biochemical tests should be carried out for confirmation.
  • Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at recommended temperature

Reference

  • Bacteriological Analytical Manual, 8th Edition, Revision A, 1998. AOAC, Washington D.C
  • British Pharmacopoeia, 201, The Stationery office British Pharmacopoeia
  • Conant N.F., 1950, Diagnostic Procedures and Reagents, 3rd Ed., APHA, Inc., New York, p. 452.
  • Carlier G. I. M., 1948, Brit. J. Derm. Syph., 60:61.

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About the Author: Labweeks

KEUMENI DEFFE Arthur luciano is a medical laboratory technologist, community health advocate and currently a master student in tropical medicine and infectious disease.

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