CRITERION™ VIOLET RED BILE (VRB) AGAR

Cat. no. C7260 CRITERION™ Violet Red Bile Agar 73gm
Cat. no. C7261 CRITERION™ Violet Red Bile Agar 500gm
Cat. no. C7262 CRITERION™ Violet Red Bile Agar 2kg
Cat. no. C7263 CRITERION™ Violet Red Bile Agar 10kg
Cat. no. C7264 CRITERION™ Violet Red Bile Agar 50kg

INTENDED USE

Hardy Diagnostics CRITERION™ Violet Red Bile Agar is recommended for the detection of coliforms in food or dairy products.

SUMMARY

Violet Red Bile (VRB) Agar is a selective medium used to detect and enumerate lactose-fermenting coliform microorganisms. The medium is recommended for use in the microbiological analysis of milk and other dairy products and for use in the examination of water.(1,2)

The medium contains bile salts and crystal violet which serve as inhibitory agents toward some gram-positive microorganisms, especially staphylococci. Neutral red is employed as the pH indicator.

Lactose-fermenting microorganisms produce pink to red colonies that are generally surrounded by a reddish zone of precipitated bile. Non-lactose-fermenting microorganisms result in colorless colonies.

FORMULA

Gram weight per liter: 36.6gm/L
Lactose 10.0gm
Pancreatic Digest of Gelatin 7.0gm
Sodium Chloride 5.0gm
Yeast Extract 3.0gm
Bile Salts No. 3 1.5gm
Neutral Red 30.0mg
Crystal Violet 2.0mg
Agar 10.0gm

Final pH 7.4 +/- 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 reddish-beige.

Store the prepared culture media at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

1. Suspend 36.6gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely. Avoid overheating.

3. Do not autoclave.

4. Cool to 45-46ºC. and dispense 15-20ml into 100mm Petri dishes containing inoculum. Rotate the plate carefully to distribute the inoculum.

5. After solidification of the inoculated medium, evenly add a cover of 4ml of the cooled (45-46 degrees C.) agar medium.

PROCEDURE

Sample Collection: Consult listed references for information on sample collection.(1-3)

Method of Use: Allow medium to warm to room temperature prior to inoculation. Consult listed references for information concerning inoculation procedures.(1-3)

INTERPRETATION OF RESULTS

Lactose-fermenting microorganisms, including coliforms, produce pink to red colonies that are generally surrounded by a reddish zone of precipitated bile.

Surface colonies of Escherichia coli appear as entire-edged colonies, while deep colonies appear lens-shaped.

Colonies of Enterobacter aerogenes often appear mucoid and pinkish in color.

Enterococci spp. may grow, and if so, usually appear pinpoint in size and rose colored.

Non-lactose-fermenting microorganisms produce colorless colonies.

LIMITATIONS

Violet Red Bile Agar contains a low concentration of bile salts, and therefore is not completely specific for enterics.

Enterococci may grow, and if so, usually appear pinpoint in size and rose colored.

In using this selective medium, best results will be obtained if it is not subjected to autoclave sterilization since organisms not killed by the boiling required to dissolve the medium, will not form colonies during the 24 hour incubation period. Following boiling to dissolve the medium completely, it is ready for use. The plates should not be incubated longer then 24 hours, inasmuch as the organisms whose growth has been suppressed, may develop and confuse the count. Best results are obtained of plates are not too heavily seeded.

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
Enterobacter aerogenes
ATCC ® 13048
A 18-24hr 35°C Aerobic Growth; pink to red colonies, may have a slight precipitate around colonies
Escherichia coli
ATCC ® 25922
A 18-24hr 35°C Aerobic Growth; pink to red colonies with a red precipitate around colonies
Salmonella enteritidis
ATCC ® 13076
A 18-24hr 35°C Aerobic Growth; colorless colonies
Staphylococcus aureus
ATCC ® 25923
B 18-24hr 35°C Aerobic Partial to complete inhibition

User Quality Control

PHYSICAL APPEARANCE

CRITERION™ Violet Red Bile Agar powder should appear homogeneous, free-flowing, and reddish-beige in color. The prepared media should appear slightly opalescent, and reddish-purple in color.

REFERENCES

1. American Public Health Association. Standard Methods for the Examination of Dairy Products, APHA, Washington, D.C.

2. American Public Health Association. Standard Methods for the Examination of Water and Wastewater, APHA, Washington, D.C.

3. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods, APHA, Washington, D.C.

4. Atlas, R.M. 1997. Handbook of Microbiological Media, 2nd ed. CRC Press, Boca Raton, FL.

5. U.S. Food and Drug Administration. Bacteriological Analytical Manual. AOAC, Arlington, VA.
http://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/ucm2006949.htm.

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

062916gr