CULTURE MEDIA – Lablink

MYCOBIOTIC OR MYCOSEL AGAR

Mycobiotic or Mycosel selective medium principally formulated for the isolation of dermatophytes but also used for the isolation of other pathogenic fungi from specimens contaminated with saprophytic fungi and bacteria.

The medium consists primarily of peptones from a pancreatic digest of soybean meal and dextrose. The selective agents are cycloheximide and chloramphenicol.

Cycloheximide inhibits the faster-growing saprophytic fungi. Chloramphenicol inhibits Gram-negative and Gram-positive organisms. Susceptibility to cycloheximide may be used for identification of fungi.

WATER AND CORNMEAL AGAR

WATER AGAR

Water agar is a nutritionally-deficient media known to enhance production of spores and conidia of sporulation. Media Preparation

• Mix 20 grams of agar in 1 litre of distilled water.

•Bring reagents to a boil.

• Autoclave at 15 lb/in2 for 15 minutes.

• Cool in slanted position or store as butts to be melted down and used as slants or plates as needed.

CORNMEAL TWEEN-80 AGAR

CMT agar is a well-established medium used for cultivation of fungi as well as to study chlamydospores production by Candida species and other yeasts.

CHROMOGENIC BISMUTH GLYCINE GLUCOSE YEAST (BIGGY)

Agar BiGGY agar is a partially selective and differential medium for the cultivation and identification of Candida species from pure cultures or clinical specimens.

Candida species, through a process of substrate reduction, reduces the bismuth salt to bismuth and sulfite to sulfide. Bismuth and sulfide combine to form a brownish to black precipitate that stains colonies and may diffuse into the medium.

Also bismuth and sulfur compounds are inhibitory to many bacteria. Yeast extract and glucose provide essential nutrients for growth. Glycine is an additional nutrient, but also inhibits many bacterial species at the high concentration used in this medium.

POTATO DEXTROSE AGAR (PDA)

Is a general purpose medium for a wide range of yeasts and molds.

The nutritionally rich base (potato infusion) encourages mold sporulation and pigment production in some dermatophytes like Trichophytan rubrum.

Most fungi thrive on Potato Dextrose Agar (PDA), but this can be too rich for many fungi, so that excessive mycelial growth is obtained at the expense of sporulation.

Is composed of dehydrated potato infusion, dextrose and agar. 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.

It is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification.

BRAIN HEART INFUSION (BHI) BROTH AND AGAR

It is a non-selective fungal culture medium that permits the growth of virtually all clinically relevant fungi. It is used for the primary recovery of saprophytic and dimorphic fungi.

The medium contains proteose peptone and infusions from calf brain and beef heart which serve as sources of carbon, nitrogen, essential growth factors, amino acids and vitamins. Dextrose is used as a source of energy. Disodium phosphate helps in maintaining the buffering action of the medium whereas sodium chloride maintains the osmotic equilibrium of the medium.

BHI with 10% defibrinated sheep blood is useful for isolation and cultivation of Histoplasma capsulatum and other fungi.

One can culture food, blood and water samples at 35–37°C for 24–48 hours for the isolation of Candida albicans. Some fungi might require more incubation time.

After the incubation period, examine tubes for turbidity which is an indication of growth. If desired, a loopful of the culture broth can then be sub-cultured onto an appropriate solid medium to observe colony morphology.

It is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification.

MALT EXTRACT AGAR (MEA)

Malt Extract Agar is used for the cultivation of fungi and is not intended for use in the diagnosis of disease or other conditions in humans. It is frequently used for culturing fungi from soil, wood, basidiomycetes etc. However, clinical specimens such as skin scrapings can be processed on the medium.

It is recommended for the detection, isolation, maintenance and enumeration of yeasts and moulds such as Aspergillus brasiliensis, Candida albicans and Saccharomyces cerevisiae.

An acidic medium which will support the growth of most yeasts and molds whilst inhibiting most bacteria.

Selectivity can be increased by further lowering the pH with the addition, after sterilization, of Lactic Acid (X037).

It should be noted that excess heating of this medium together with its low pH can easily result in hydrolysis of the agar gel producing soft plates.

The medium consists of malt extract, peptone and agar.

Cultural characteristics observed after an incubation at 25-30°C for 48-72 hours at a pH of 5.4±0.2.

Further biochemical tests must be carried out for further identification

SABOURAUDS DEXTROSE AGAR (SDA)

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

It is nutritionally poor with acidic pH (5.6).

Peptone (Enzymatic Digest of Casein and Enzymatic Digest of Animal Tissue) provide 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.

Not recommended as a primary isolation medium because it is insufficiently rich to recover certain fastidious pathogenic species, particularly most of the dimorphic fungi.

It does not promote conidiation of filamentous fungi.

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.

Identification of fungi is performed by observing various aspects of colony morphology, characteristic microscopic structures, rate of growth, media which supports the organism’s growth, and source of specimen.

Yeasts will grow as creamy to white colonies. Molds will grow as filamentous colonies of various colors.