Principles of the Procedure
Yeast extract is a source of trace elements, vitamins and amino
acids. Malt extract is a source of carbon, protein and nutrients.
Peptone is an additional source of carbon and provides nitrogen
and amino acids. Dextrose provides carbon. Agar is the
solidifying agent.
Expected Results
Examine the plates or tubes for growth. Record YM Agar
results as colony-forming units (CFU) per volume of sample.
Record YM Broth results as growth or no growth.
Intended Use
YM Agar and YM Broth are used for cultivating yeasts, molds
and other aciduric microorganisms.
Summary and Explanation
YM Agar and YM Broth are prepared according to the formulae
published by Wickerham.1-3 Wickerham suggested that YM Broth
acidified to pH 3.0-4.0 be used as an enrichment medium for
yeasts from populations also containing bacteria and molds.
Media selectivity may be enhanced through acidification or
through addition of selective agents. YM Broth may be acidified
prior to sterilization. YM Agar should be sterilized without pH
adjustment and sterile acid added to the sterile molten medium
cooled to 45-50°C. Acidified YM Agar should not be heated.
Antibiotics may be aseptically added to the sterile media. Other
fungistatic materials, such as sodium propionate and diphenyl
may be added to YM Agar to eliminate molds and permit the
enumeration of yeasts in mixed populations.