產品名稱：VIOLET RED BILE LACTOSE AGAR
貨號：oxoidL CM0107
規(guī)格：500g
VIOLET RED BILE LACTOSE AGAR
Code：CM0107
Description
Violet Red Bile Lactose Agar 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 1,2.
Organisms which rapidly attack lactose produce purple-pink 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.3 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.
Technique
Druce et al. recommended the following procedures:
For the routine determination of the coli-aerogenes content of raw milk, prepare pour-plates containing 1.0, 0.1 and 0.01ml of the sample in Violet Red Bile Lactose Agar, and incubate for 20-24 hours at 35°C.
For coli-aerogenes counts of pasteurised milk, employ 4 pour-plates of Violet Red Bile Lactose Agar. Divide 10ml of the sample among three of the plates, and add 1ml of the sample to the remaining plate. Incubate for 20-24 hours at 30°C. Similarly the examination of rinses and swabs from dairy equipment and apparatus, should include the spreading of 10ml of solution on each of 3 plates and of 1ml on a single plate. Coliform organisms form purple-pink colonies which are 1 to 2mm in diameter, usually surrounded by a purple zone. Occasionally colonies may be considerably smaller （less than 0.5mm in diameter）.
When preparing pour-plates the medium should be freshly made up, cooled to 47°C and used within 3 hours.
An overlay method is helpful to improve the specificity of the medium. In this case a thin layer of cooled molten medium is poured over the inoculated base layer and allowed to set before incubation. Incubation may be carried out at >42°C for 18 hours, 30°C for 24-48 hours or 4°C for 10 days, depending on the temperature characteristics of the organisms to be recovered. For Escherichia coli a temperature of 44 ± 1°C is specifically recommended 4.
Characteristic appearance of colonies
Round, purple-pink may be surrounded by purple haloes （lactose-positive organisms）.
Pale, may have greenish haloes （lactose-negative organisms）.
Confirmation of the identity of purple-pink colonies must be made by further tests.
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.