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Chapter 113 : Reagents, Stains, and Media: Mycology
A variety of stains, media, and reagents are available to the mycology laboratory for the detection, isolation, characterization, and identification of yeasts and moulds. Media should be carefully selected based on specimen type and suspected fungal agents. These media include cornmeal agar, inhibitory mould agar, inhibitory mould agar with gentamicin, soy peptone agar with cycloheximide/chloramphenicol without pH indicators, potato dextrose agar, brain heart infusion agar with 5% sheep blood containing chloramphenicol/gentamicin, Sabouraud's dextrose agar, and Sabouraud's dextrose agar with chloramphenicol/gentamicin. Nonexempt media that require specific quality assurance testing include cornmeal agar with Tween, brain heart infusion agar with 5% sheep blood and cycloheximide/chloramphenicol, bismuth sulfite-glucose-glycine-yeast (BiGGY) agar, birdseed agar, brain heart infusion with 5% sheep blood and penicillin/streptomycin, dermatophyte test medium, and potato flakes agar with or without cycloheximide/chloramphenicol. The stains, media, and reagents listed in this chapter include those commonly used and a few specialized items. Methenamine silver stains are perhaps the most useful stains for visualizing fungi in tissue. Specific colonial morphologies and growth patterns of the different Candida species are also detected. Assimilation broth media for yeasts are used for the detection of assimilation, i.e., carbohydrate utilization by yeasts in the presence of oxygen. A brief description of selected chromogenic agar products that are FDA approved for use in U.S. laboratories is provided as an overview of how different yeasts react with chromogenic substrates and the resultant characteristic colony color.