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Dehydrated Culture Media

VIOLET RED BILE AGAR (VRBA) with MUG

CODE: CM0978

A lactose-containing selective medium for the detection and enumeration of coliform organisms in water, food and dairy products.

Typical Formula*

gm/litre

Yeast extract

3.0

Peptone

7.0

Sodium chloride

5.0

Bile Salts No.3

1.5

Lactose

10.0

Neutral red

0.03

Crystal violet

0.002

Agar

12.0

4-methylumbelliferyl-ß-D-glucuronide (MUG)

0.1

pH 7.4 ± 0.2 @ 25°C

 
* Adjusted as required to meet performance standards

Directions
Suspend 38.6g of VRBA with MUG in 1 litre of distilled water. Bring to the boil to dissolve completely. No further sterilisation is necessary or desirable. Mix well before pouring into sterile petri dishes.

Description
VRBA with MUG is a Standard Methods medium recommended by FDA/BAM1.

The medium is based on Violet Red Bile Lactose Agar (VRBLA) (CM0107) which is a selective medium for the detection and enumeration of coliform organisms. The medium has been used for the determination of the coli-aerogenes content of water, milk and other dairy products, dairy equipment, and food products etc.

Organisms which rapidly attack lactose produce purple colonies surrounded by purple haloes. Non-lactose or late-lactose fermenters produce pale colonies with greenish zones. Other related Gram-negative bacteria may grow but can be suppressed by incubation at >42°C or by anaerobic incubation.

Druce et al. found that Violet Red Bile Lactose Agar was as good an indicator of coli-aerogenes bacteria in milk as MacConkey Broth, and that the Oxoid medium was suitable for determining the coli-aerogenes content of milk.

VRBA with MUG contains 4-methylumbelliferyl-ß-D-glucuronide (MUG) as a substrate which is cleaved by the enzyme ß-glucuronidase produced by Escherichia coli resulting in a fluorescent end-product.

NaOH addition generally improves fluorescence by increasing the alkalinity of the solution. An increase in fluorescence can also be achieved by increasing the level of MUG added to the base medium.

For further information about MUG see MUG Reagent (BR0071).

Storage conditions and Shelf Life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C and use as freshly as possible.

Appearance
Dehydrated medium: Straw-pink coloured, free-flowing powder
Prepared medium: Dark purple coloured gel

Quality control

Positive control:

Expected results

Escherichia coli ATCC® 25922 *

Good growth; purple-pink colonies with fluorescence

Negative control:

 

Staphylococcus aureus ATCC® 25923 *

No growth

* This organism is available as a Culti-Loop®

References
1."Association of Official Analytical Chemists" F.D.A. Bacteriological Analytical Manual 8th Edition (Revision A/1998) AOAC, Arlington Va.

 
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