Some bacteria can produce enzymes (lipases) that hydrolyze lipids like fats, oils, lecithins, sterols etc. Lipases are used by bacteria
for the hydrolyse of phospholipid in cell membranes, allowing skin and subcutaneous tissues colonization.
Medium preparation (Egg Yolk Agar):
1. Prepare an egg yolk solution harvesting sterile yolks* and mixing 1:1 with
physiological saline solution.
2. To Nutritive Agar enriched with 1% NaCl, add 10% egg yolk mix. Pour in Petri
plates. For liquid media use Nutritive Broth instead of Nutritive Agar.
Inoculate the plate and incubate at 37 ºC for 1 to 4 days.
Reaction is positive if a clear area appears around colonies. Keeping the plates 30
minutes in the refrigerator will make the reaction more visible, as the lipids became
more opaque at low temperature.
How to aseptically transfer the egg content: clean the eggs thoroughly with wet gauze,
place in a container, cover with 80% alcohol (vol) and let stand for 2 hours. Decant the
alcohol. Dry the eggs cautiously flaming then, aseptically, break the shell in half and
drop the separated yolk into a sterile recipient.
1. H. Raducanescu, V. Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres,
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown Publishers.
3. Augustus B. Wadsworth: Standard Methods of the Division of Laboratories and
Research of the New York State Department of Health. 1947, The Williams & Wilkins
(c) Costin Stoica