描述
- Formula* per Liter: Pancreatic Digest of Gelatin........... 7.0g Yeast Extract ................................. 3.0g Bile Salts #3 ................................. 1.5g Agar .............................................15.0g MUG ............................................ 0.05g Lactose .......................................10.0g Sodium Chloride.......................... 5.0g Neutral Red ................................ 0.03g Crystal Violet .............................. 0.002g
- Final pH: 7.4 ± 0.2 at 25.0°C * Grams per liter may be adj. or formula supplemented to obtain desired performance
- Preparation: Mix 41.6 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for two minutes. DO NOT AUTOCLAVE. Cool to 40° to 45°C and dispense 15-20 mL into 100 mm Petri dishes containing inoculum. After solidification of the inoculated medium, evenly add a cover of 4 mL of the cooled (45°- 46.0°C) agar medium.
- Quality Control Specifications: 1. The powder is homogeneous, free flowing and light reddish-beige. 2. Visually the prepared medium is clear to slightly hazy and reddish purple. 3. Expected cultural response after 18-24 hours at 35.0°C.
- Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light pinkish-beige color.
Use: Selective Agar medium used for the fluorogenic detection of Escherichia coli in food, milk, water and other sanitary materials. Description: Violet Red Bile Agar is recommended for use in the microbiological analysis of milk and other dairy products and for use in the examination of water. Violet Red Bile Agar is a selective medium which detects the growth of lactose fermenting coliforms. Coliforms colonies lower the pH of the medium subsequently causing their colonies to look red (neutral red dye) and to precipitate the bile salts. Crystal violet and bile salts inhibit the growth of Gram positive microorganisms. The addition of 4- methylumbelliferyl-B-D-glucuronide (MUG) allows for the rapid detection of E. coli when the incubated medium is observed for fluorescence using a long-wave UV light (365 nm) source. It can also detect anaerogenic E. coli strains. Most strains of E coli produce B-glucuronidase which hydrolyzes MUG to the fluorogenic compound 4-methyl-umbelliferone. Studies by Feng and Hartman noted that most E. coli strains (96%) and all enterotoxigenic E. coli strains (100%) and a moderate number of Salmonella (1 7%) and Shigella (40%) stains produce B-glucuronidase. False positives can also be caused by Streptococcus sp.
