| Technique | LECITHIN EGG YOLK ,(/,)/,( |
| Principle | Several Bacillus and Clostridium species produce lecithinase and proteases. The presence of these enzymes can be detected on Lactose-Egg Yolk-Milk agar (L.E.Y.). Lecithinase production may be selectively inhibited by inoculating one half of the plate with antitoxin before inoculating the plate with the culture under study. The antitoxin neutralizes the lecithinase but it does not inhibit the growth of the microbes. |
| Cautions | |
| Method | Streak one L.E.Y. plate with a
Bacillus spp and incubate aerobically. Streak a second
plate with a Clostridium spp and incubate anaerobically. Optionally Flood the plate with saturated aq. copper sulphate.. |
| Results | The lactose and neutral red will
allow for detection of lactose fermentation, by
development of a deep red colour in and around growth
areas. Proteolytic enzymes will attack the milk,
resulting in a clearing of the medium. Lecithinases split
lecithovitellin (present in egg yolks) into lecithin and
fatty acids. The insoluble lecithin is demonstrated by a
"pearly layer" or opalescence around the
colonies If the plate is flooded with saturated aq. copper sulphate an insoluble greenish-blue copper soap is formed where the lecithinases digested the lecithovitellin and released fatty acids. |
| Positive control | |
| Negative control | |
| Reagents | |
| Reference |