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
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 °C 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
1. H. Raducanescu, V. Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres,
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C.
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 Company.
(c) Costin Stoica