Description
| Intended Use and Principle of Procedure |
| Violet Red Bile Glucose Agar is used to detect and enumerate Enterobacteriaceae in foods and dairy products.
Violet Red Bile Glucose Agar contains peptone as a source of carbon, nitrogen, vitamins, and minerals. Yeast extract supplies B-complex vitamins, which stimulate bacterial growth. Glucose is a carbohydrate. Bile salts and crystal violet inhibit gram- positive bacteria. Glucose fermenters produce red colonies with red-purple halos (bile precipitation) in the presence of neutral red, a pH indicator. Agar is the solidifying agent. |
| Summary and Explanation |
| The Enterobacteriaceae group includes lactose-fermenting coliform bacteria, lactose-nonfermenting strains of E. coli, and lactose-nonfermenting species, such as Salmonella and Shigella. When examining some foods, it is desirable to detect Enterobacteriaceae rather than the coliform bacteria.
Enterobacteriaceae are glucose-fermenting bacteria. Mossel et al. 3 modified lactose-containing Violet Red Bile Agar by adding glucose to improve the recovery of Enterobacteriaceae. Later work by Mossel et al.4,5 demonstrated that lactose could be omitted, resulting in the formulation known as Violet Red Bile Glucose Agar (VRBGA).
The Hycheck hygiene contact slide is a double-sided paddle containing two agar surfaces for immersing into fluids or sampling surfaces. There is one slide containing Violet Red Bile Glucose Agar paired with Tryptic Soy Agar. |
| Formulae | ||||||||||||||||
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| Procedure |
| This medium can be used in spread or pour plate procedures, with or without an overlay. In addition, this medium can be used as an overlayer for spread plates to both prevent swarming colonies and provide semi-anaerobic conditions that suppress the growth of non fermentative gram-negative organisms. Stab inoculation procedures can also be used with this medium. |
| Directions for Preparation from Dehydrated Product |
| 1. Suspend 41.5 g of the powder in 1 L of purified water. Mix thoroughly. 2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder. DO NOT AUTOCLAVE. 3. Test samples of the finished product for performance using stable, typical control cultures. |
| Identification Specification and Cultural Response | |||||||||||||||||||||||||||||||||||||
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| Limitations Of The Procedure |
| When used in the pour plate procedure, the medium should be freshly prepared, tempered to 47°C, and used within 3 hours. |
| Expected Results |
| Enterobacteriaceae ferment glucose, produce acid products, and form red to dark purple colonies surrounded by red-purple halos.
Subculture colonies of interest so that positive identification can be made by means of biochemical testing and/or microscopic examination of organism smears. |
| References |
5. Mossel, Eelderink, Koopmans and van Rossem. 1979. J. Food Protect. 42:470. |
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