VIOLET RED BILE AGAR (VRBL)
INTENDED USE
Violet Red Bile Agar (VRBL) is a selective medium used for the detection and enumeration of coliform
bacteria in water, milk, dairy and other food products.
HISTORY
A large number of researchers have studied this medium. MacCrady in 1932 for the Committee of
Standard Methods of Milk Analysis of the American Public Health Association, Bartram and Black for
the isolation of coliform bacteria in raw and pasteurized milk, and also Miller and Prickett in a note
concerning the recontamination of milk. All these authors found the medium satisfactory since
complete results were obtained within 24 hours of incubation.
PRINCIPLES
- The simultaneous presence of crystal violet and bile salts inhibit Gram-positive bacteria.
- Lactose fermentation results in acidification of the medium, shown by the red color of the pH
indicator (neutral red) and by the precipitation of bile acids around the colonies.
PREPARATION
-
Suspend 38.5 g of dehydrated medium (BK152) in 1 liter of distilled or deionized water.
Slowly bring to boiling, stirring until complete dissolution.
Do not overheat.
Do not autoclave.
With the ready-to-use base media (BM034 or BM035), melt the medium with the minimum amount
of time necessary in order to achieve total liquefaction.
NOTE :
MUG (4-methylumbelliferyl--D-glucuronide) can be added to the medium in order to detect
Escherichia coli (refer to the monograph on MUG Supplement, BS024).
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INSTRUCTIONS FOR USE
-
Cool and maintain the medium at 44-47°C.
Transfer 1 mL of the product to analyze and its tenfold dilutions to Petri dishes.
Pour in 12 mL of medium.
Homogenize by swirling.
Let solidify on a cold surface.
Overlay the solidified agar with 4 mL of medium.
Let solidify.
Incubate :


at 30°C for 24 hours for the detection and enumeration of coliform bacteria,
at 44°C for heat-tolerant coliform bacteria.
RESULTS
Coliform bacteria form violet colonies whose diameter is equal to or greater than 0.5 mm after 24
hours of incubation. Lactose-negative enterobacteria are colorless. In the context of the protocol
described in NF ISO 4832, it may be necessary to confirm atypical colonies via gas production in
Brilliant Green Bile broth BGBB (BK002, BM011).
TYPICAL COMPOSITION
(can be adjusted to obtain optimal performance)
For 1 liter of medium :
- Peptic digest of meat .......................................................................7.0 g
- Yeast extract ....................................................................................3.0 g
- Lactose ..........................................................................................10.0 g
- Bile salts...........................................................................................1.5 g
- Sodium chloride ...............................................................................5.0 g
- Neutral red ..................................................................................30.0 mg
- Crystal violet..................................................................................2.0 mg
- Bacteriological agar .......................................................................12.0 g
pH of the ready-to-use medium at 25°C : 7.4 ± 0.2.
QUALITY CONTROL
- Dehydrated medium : beige to pinkish-beige powder, free-flowing and homogeneous.
- Prepared medium : reddish agar.
- Typical culture response after 24 hours of incubation at 30°C and at 44°C:
Microorganisms
Escherichia coli
*Escherichia coli
Pseudomonas aeruginosa
Enterococcus faecalis
Growth
(Productivity ratio : PR)
Characteristics
PR  50%
PR  50%
good, score 2
inhibited, score 0
violet-red colonies
violet-red colonies
pinkish-beige colonies
ATCC® 25922
ATCC 8739
ATCC 27853
ATCC 29212
* For ready-to-melt media BM03408 and BM03508, this strain is only tested at 30°C.
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STORAGE / SHELF LIFE
Dehydrated medium : 2-30°C.
- The expiration date is indicated on the label.
Prepared medium (benchmark value*) :
- Use on the day of preparation.
Ready-to-melt media in vials:
- Store between 2-14°C, shielded from light.
- The expiration date is indicated on the label.
MUG 50 mg Supplement :
- Store between 2-8°C, shielded from light.
- The expiration date is indicated on the label.
PACKAGING
Code
Ready-to-melt media in vials :
- 10 x 100 mL
- 10 x 200 mL
BM03408
BM03508
Dehydrated medium :
- 500 g bottle
- 5 kg drum
BK152HA
BK152GC
MUG 50 mg Supplement :
- 10 vial pack
BS02408
BIBLIOGRAPHY
XP CEN ISO/TS 11133-2 (V 08-104-2). Janvier 2004. Microbiologie des aliments. Guide pour la préparation et la production
des milieux de culture. Partie 2 : Guide général pour les essais de performance des milieux de culture.
NF ISO 4832 (V 08-015). Juillet 2006. Microbiologie des aliments. Méthode horizontale pour le dénombrement des
coliformes. Méthode par comptage des colonies.
NF V08-050. Avril 2009. Microbiologie des aliments. Dénombrement des coliformes présumés par comptage des colonies
obtenues à 30°C .
NF V08-060. Avril 2009. Microbiologie des aliments. Dénombrement des coliformes thermotolérants par comptage des
colonies obtenues à 44°C.
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Biokar Diagnostics – Rue des Quarante Mines – ZAC de Ther – Allonne – B.P. 10245 – F60002 Beauvais Cedex – France
Tél : + 33 (0)3 44 14 33 33 – Fax : + 33 (0)3 44 14 33 34 – www.biokar-diagnostics.com
PHOTO SUPPORT
Product reference : BK152HA, GC, BM03408, BM03508
Media used for : Selective detection and enumeration of coliform bacteria in foods.
Escherichia coli
Violet Red Bile agar (VRBL)
Ref : BK152HA
Incubation : 24 hours / 30°C
Characteristics : violet-red colonies surrounded by tight halos of precipitated bile.
*Benchmark value refers to the expected shelf life when prepared under standard laboratory conditions following manufacturer’s instructions. It is provided as a
guide only and no warranty, implied or otherwise is associated with this information.
The information provided on the package takes precedence over the formulations or instructions described in this document.
The information and specifications contained in this technical data sheet date from 2009-07-31.
They are susceptible to modification at any time, without warning.
Code document : BK152/A/2003-01 : 6.
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Biokar Diagnostics – Rue des Quarante Mines – ZAC de Ther – Allonne – B.P. 10245 – F60002 Beauvais Cedex – France
Tél : + 33 (0)3 44 14 33 33 – Fax : + 33 (0)3 44 14 33 34 – www.biokar-diagnostics.com