Purpose
This test is of value in differentiation of Erwinia species
Materials
| Ingredient | 525 mL |
|---|---|
| Distilled water | 250 mL |
| nutrient agar | 250 mL |
| beef extract | 0.25 g |
| yeast extract | 0.5 g |
| peptone | 1.25 g |
| sodium chloride (NaCl) | 1.25 g |
| agar | 3.75 g |
| egg yolk emulsion | 25 mL |
Instructions
- mix all ingredients except the egg yolk emulsion
- Autoclave
- Cool to 50-55°C
- Prepare egg yolk emulsion
- Take a fresh hen egg, washed well in a soap solution, rinsed and surface-sterilized in 70% ethanol for 5 minutes.
- The egg is flamed, broken aseptically, and the yolk is separated into a sterile measuring cylinder.
- Dilute to 40% v/v with sterile, distilled water.
- Add egg yolk emulsion. The emulsion is incorporated into molten nutrient agar at a rate of 10 ml/100 ml of medium (10 ml yolk in 15 ml water equals 25 ml emulsion), just before plates are poured.
Expected results
- The phospholipid emulsion of egg yolk is broken down by lecithinase, liberating a turbid zone of free fats around a lecithinase (+) colony.
Notes
- Plates will keep refrigerated for 2 months.
References
- Fahy, P. C. and G. J. Persley. 1983. Plant Bacteria Diseases, A Diagnostic Guide. Academic Press, NY. 393 pp. ( p. 359, p. 393.)
Contributed by
From the Virginia Polytechnic Institute and State University Mediabook; Orignially created by Robert Wick; contributed by Mary Ann Hansen
