Part of Thermo Fisher Scientific
Organisms this product works with:
Other products used in the isolation of Escherichia coli:
VIOLET RED BILE LACTOSE AGAR (ISO)
Violet Red Bile Lactose (VRBL) Agar (ISO) is for the detection and enumeration of coliforms in food, animal feed and environmental samples. This medium meets the formulation and performance criteria laid down in ISO 4832:20061 and ISO/TS 11133-2:20032.
|Bile salts No. 3|
|pH 7.4 ± 0.2 @ 25°C|
Suspend 38.5g of VRBL Agar (ISO) dehydrated medium in 1 litre of distilled water. Bring to the boil while mixing. Continue to boil for up to 2 minutes or for the minimum time necessary to dissolve completely. DO NOT AUTOCLAVE. Cool to 44-47°C and use within 4 hours. Mix well before pouring.
Methods for indicator or index organisms provide a simple approach for routine screening of foods. Besides safety, indicator groups provide a measure of food quality and spoilage potential. One of the most common groups of bacteria employed as indicator organisms by the food industry are the coliforms, which can be regarded as a subgroup within the Enterobacteriaceae.
Coliforms are commonly defined by their ability to ferment lactose rapidly, producing acid and gas, typically within 24 hours. The genera that would be commonly expected to belong to this group include Enterobacter, Klebsiella, Citrobacter and Escherichia, particularly Escherichia coli. However, species belonging to other genera, for example Erwinia and Serratia, can also ferment lactose, albeit slowly, and some strains of Citrobacter and Klebsiella, as well as Salmonella arizonae and Hafnia alvei, show delayed or variable fermentation ability.
Coliforms rapidly ferment the lactose in VRBL Agar (ISO) and so reduce the pH of the medium, producing red-purple colonies, due to the inclusion of neutral red and crystal violet. These colonies are usually surrounded by red-purple halos of precipitated bile salts.
Non-lactose or late lactose fermenters produce straw or colourless colonies with greenish halos. Other related Gram-negative bacteria may grow but can be suppressed by incubation at >42°C or by anaerobic incubation. Crystal violet and bile salts inhibit the growth of Gram-positive flora.
According to ISO/TS 11133-2:20032, VRBL Agar (ISO) should deliver a productivity ratio of ≥0.5 for E. coli when compared to the same inoculum grown on a reference medium (Tryptone Soya Agar). VRBL Agar (ISO) is tested in line with the requirements of ISO/TS 11133-2:20032. Quality certificates indicating organisms tested and productivity are available for every batch.
Refer to the appropriate standard method for full instructions. The following is an overview of ISO 4832:20061.
Storage conditions and Shelf life
VRBL (ISO) should be stored in the tightly capped original container at 10-30°C. When stored as directed, the un-opened product will remain stable until the expiry date printed on the packaging.
Locally prepared VRBL (ISO) plates can be stored for up to 2 weeks when made from CM0968 according to the manufacturer’s instructions and stored at 2-8°C, out of direct sunlight. A longer shelf life may be attainable, but should be validated under the relevant, local manufacturing and storage conditions.
Dehydrated medium: Straw-pink, free-flowing powder
Prepared medium: Dark purple gel
|Positive controls:||Expected results|
|Escherichia coli ATCC® 25922*||Red-purple colonies with or without halos|
|Pseudomonas aeruginosa ATCC® 27853*||Colourless to straw coloured colonies|
|Enterococcus faecalis ATCC® 29212*||No growth|
VRBL Agar (ISO) should be prepared, cooled to 44-47°C and used within 4 hours.
VRBL Agar (ISO) is for laboratory use only. Do not use the dehydrated medium beyond the stated expiry date or if the product shows any sign of deterioration.
1. ISO 4823:2006
2. ISO/TS 11133-2:2003
3. ISO 6887
4. ISO 826
ATCC® is a registered trademark of American Type Culture Collection