CRITERION™ WL DIFFERENTIAL MEDIUM and
WL NUTRIENT MEDIUM

Cat. no. C7290 CRITERION™ WL Differential Medium 160gm
Cat. no. C7291 CRITERION™ WL Differential Medium 500gm
Cat. no. C7292 CRITERION™ WL Differential Medium 2kg
Cat. no. C7293 CRITERION™ WL Differential Medium 10kg
Cat. no. C7294 CRITERION™ WL Differential Medium 50kg
Cat. no. C7300 CRITERION™ WL Nutrient Medium 160gm
Cat. no. C7301 CRITERION™ WL Nutrient Medium 500gm
Cat. no. C7302 CRITERION™ WL Nutrient Medium 2kg
Cat. no. C7303 CRITERION™ WL Nutrient Medium 10kg
Cat. no. C7304 CRITERION™ WL Nutrient Medium 50kg

INTENDED USE

Hardy Diagnostics CRITERION™ WL Differential Medium is used for isolating bacteria encountered in brewing an industrial fermentation processes.

Hardy Diagnostics CRITERION™ WL Nutrient Medium is used for cultivating yeasts, molds, and bacteria encountered in brewing and industrial fermentation processes.

WL Nutrient Medium can support the growth of bacteria, but unless the yeast cell titer is small the bacteria may not be detected. Consequently, WL Differential Medium was created to inhibit the growth of yeasts without inhibiting the growth of bacteria present in beers.

SUMMARY

WL Nutrient Medium, also known as Wallerstein Laboratory Medium, was developed by Green and Gray while studying various fermentation processes.(4,5) WL Differential Medium and WL Nutrient Medium are used simultaneously as a set of three plates. One plate is prepared from WL Nutrient Medium and two plates from WL Differential Medium.(6) The WL Nutrient Medium plate is incubated aerobically to obtain a total count of mainly yeasts colonies. A second WL Differential Medium plate is incubated aerobically for growth and acetic acid bacteria including Flavobacterium, Proteus and thermophilic bacteria. A third WL Differential Medium plate is incubated anaerobically for growth of lactic acid bacteria andPediococcus.

WL Differential and Nutrient Media contain a variety of substances to promote the growth and selection of bacteria and yeast. Yeast extract is a source of trace elements, vitamins and amino acids. Pancreatic digest of casein provides nitrogen, amino acids, and carbon. Dextrose is the source of carbohydrate. Monopotassium phosphate buffers the media. Potassium chloride, calcium chloride, and ferric chloride are essential ions and help to maintain osmotic balance. Manganese sulfate and magnesium sulfate are sources of divalent cations. Bromcresol green is a pH indicator. Agar is the solidifying agent in WL Differential and WL Nutrient Media. Actidione (cycloheximide) is added as a selective agent in WL Differential Medium to inhibit the growth of yeasts and mold. Reliable counts for brewers' yeast are obtained with WL Nutrient Medium at pH 5.5. However, a pH adjustment to 6.5 is necessary for obtaining reliable counts of baker's and distiller's yeast.

FORMULA

WL Differential Medium
Gram weight per liter: 80.0gm/L
Dextrose 50.0gm
Pancreatic Digest of Casein 5.0gm
Yeast Extract 4.0gm
Monopotassium Phosphate 0.55gm
Potassium Chloride 0.425gm
Calcium Chloride 0.125gm
Magnesium Sulfate 0.125gm
Bromcresol Green 0.022gm
Actidione 0.004gm
Ferric Chloride 0.0025gm
Manganese Sulfate 0.0025gm
Agar 20.0gm

Final pH 5.5 +/- 0.2 at 25ºC.

WL Nutrient Medium
Gram weight per liter: 80.0gm/L
Dextrose 50.0gm
Pancreatic Digest of Casein 5.0gm
Yeast Extract 4.0gm
Monopotassium Phosphate 0.55gm
Potassium Chloride 0.425gm
Calcium Chloride 0.125gm
Magnesium Sulfate 0.125gm
Bromcresol Green 0.022gm
Ferric Chloride 0.0025gm
Manganese Sulfate 0.0025gm
Agar 20.0gm

Final pH 5.5 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original light beige with greenish tint.

Store the prepared culture media at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

WL Differential Medium and WL Nutrient Medium

1. Suspend 80.0gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely.

3. Sterilize in the autoclave at 121ºC. for 15 minutes.

Note: To adjust pH to 6.5, add the amount of 1% sodium carbonate solution specified on the product label to the rehydration water before dissolving the medium.

PROCEDURE

Specimen Collection: Consult listed references for information on specimen collection.(1,3) Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport media and refrigerated until inoculation.

1. Inoculate and incubate for 40-48 hours at 35ºC. for bacteria or 30ºC. for yeasts.

LIMITATIONS

WL Nutrient Medium can support the growth of bacteria, but unless the number of yeast cells on the plate is small the bacteria may not be detected.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as autoclaves, incinerators, and incubators, etc., are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
WL Differential Medium:
Escherichia coli
ATCC ® 25922
A 40-48hr 30-35°C Aerobic Good growth
Lactobacillus fermentum
ATCC ® 9338
B 40-48hr 30-35°C Anaerobic Good growth
Saccharomyces cerevisiae
ATCC ® 9763
B 40-48hr 30-35°C Aerobic Inhibited
WL Nutrient Medium:
Saccharomyces cerevisiae
ATCC ® 9763
B 40-48hr 30-35°C Aerobic Good growth
Lactobacillus fermentum
ATCC ® 9338
B 40-48hr 30-35°C Aerobic Fair to good growth
Escherichia coli
ATCC ® 25922
A 40-48hr 30-35°C Aerobic Fair to good growth

User Quality Control

PHYSICAL APPEARANCE

CRITERION™ WL Differential Medium and WL Nutrient Medium powder should appear homogeneous, free-flowing, and light beige, with a greenish tint, in color. The prepared media should appear slightly opalescent, without significant precipitate, and bluish-green in color.

REFERENCES

1. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

2. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

3. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

4. Green, S.R. and P.P. Gray. 1950. Paper read at American Society of Brewing Chemists Meeting. Wallerstein Lab. Commun.; 12:43.

5. Green, S.R. and P.P. Gray. 1950. A differential procedure applicable to bacteriological investigation in brewing. Wallerstein Lab. Commun.; 13:357.

6. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

7. Hall, J.F. 1971. J. Inst. Brewing; 77:513-516.


ATCC is a registered trademark of the American Type Culture Collection.

062916gr