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|
Hardy Diagnostics CRITERION™ Violet Red Bile Agar is recommended for the detection of coliforms in food or dairy products.
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.
|Gram weight per liter:||36.6gm/L|
|Pancreatic Digest of Gelatin||7.0gm|
|Bile Salts No. 3||1.5gm|
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.
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.
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.
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.
|Test Organisms||Inoculation Method*||Incubation||Results|
ATCC ® 13048
|A||18-24hr||35°C||Aerobic||Growth; pink to red colonies, may have a slight precipitate around colonies|
ATCC ® 25922
|A||18-24hr||35°C||Aerobic||Growth; pink to red colonies with a red precipitate around colonies|
ATCC ® 13076
|A||18-24hr||35°C||Aerobic||Growth; colorless colonies|
ATCC ® 25923
|B||18-24hr||35°C||Aerobic||Partial to complete inhibition|
User Quality Control
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.
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.
ATCC is a registered trademark of the American Type Culture Collection.