Vitamin Free Yeast Base

Vitamin Free Yeast Base is used for studying vitamin requirements of yeasts.

Composition**

Final pH ( at 25°C): 5.6±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 16.75 grams in 100 ml distilled water containing the desired vitamins. If necessary, warm slightly to effect complete solution. This is 10X medium. Sterilize by filtration and store in refrigerator. For use dilute 0.5 ml of this with 5 ml of sterile distilled water. Shake thoroughly before inoculation.

Principle And Interpretation

Yeasts are unicellular, eukaryotic, budding cells that are generally round, oval or elongated in shape and are considered as opportunistic pathogens (1). They multiply principally by the production of blastoconidia (buds) (1). Yeast colonies are moist and creamy or glabrous to membranous in texture. Moulds are microscopic, plant-like organisms, composed of long filaments called hyphae. Both are widely distributed in soil, water and air. Cultivation of yeasts and moulds becomes important in fermentation studies where they are generally used as starter cultures. Vitamin Free Yeast Base is recommended for classification of yeasts based on vitamin requirement. It contains all essential nutrients and necessary inorganic salts for the cultivation of yeasts (2). Use a highly diluted inoculum and incubate the tubes for 7 days at 25-28°C, since with the inoculum, vitamins may also be transported. Yeast themselves are also able to carry traces of vitamins, and therefore a second inoculation in Vitamin Free Yeast Base must be performed following the same procedure as for the first inoculation. Then incubate at 25-28°C for 7 days.

L-Histidine monohydrochloride, DL-methionine and DL-tryptophan are the amino acid sources. Dextrose is an energy source. Sodium chloride, magnesium sulphate and ammonium sulphate are sources of ions that simulate metabolism. Monopotassium phosphate buffers the medium. The trace elements provide inorganic salts for the cultivation of yeasts.

Quality Control

Appearance: White to cream homogeneous free flowing powder

Colour and Clarity of prepared medium: Colourless clear solution.

Reaction: Reaction of 1.67% w/v aqueous solution at 25°C. pH : 5.6±0.2

pH: 5.40-5.80

Cultural Response

M208: Cultural characteristics observed after an incubation at 25-30°C for 6-7 days.

Storage and Shelf Life

Store dehydrated powder and the prepared medium at 2 - 8°C in tightly closed container . Use before expiry date on the label.

Reference

1. Murray P. R., Baron E. J., Jorgensen J. H., Pfaller M. A., Yolken R. H., (Eds.), 8th Ed., 2003, Manual of Clinical Microbiology, ASM, Washington, D.C.
2. Wickerham L. J., 1951, Taxonomy of yeasts, Technical bulletin No. 1029, U.S. Dept. Agriculture.