Lecithinase activity

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

1. mix all ingredients except the egg yolk emulsion
2. Autoclave
3. Cool to 50-55°C
4. Prepare egg yolk emulsion
   1. Take a fresh hen egg, washed well in a soap solution, rinsed and surface-sterilized in 70% ethanol for 5 minutes.
   2. The egg is flamed, broken aseptically, and the yolk is separated into a sterile measuring cylinder.
   3. Dilute to 40% v/v with sterile, distilled water.
5. 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