Lecithinase test can also be called as Naglers reaction. This is considered as one of the important biochemical tests which helps us to identify the organisms that has its ability to liberate the enzyme known as Phospholipases.
this biochemical test is used to identify the different organisms which has its capability to differentiate and specifically found the organisms which has its capability to liberate the enzyme lecithinases, which are also known as phospholipases. The commonly known example of one such species is Clostridium perfringens. Where as these organisms consists of the alpha toxin, which has an ability to activate the phospholipase activity in the medium which helps us to differentiate the species of Clostridium perfringens from the other Clostridium species. Apart from C. perfringes, there are also few other species which has its ability to synthesize the enzyme lecithinase such as C. baratti, C. bifermantans, C. absonum, C. sordelli, and C. novyi.
These species produce an enzyme lecithinase by neutralizing the activity of lecithin C by producing an antitoxin. Phosphatidylcholine or lecithin is a substance which is found abundantly in the animal tissues, egg yolk and few higher plants, which consists of phospholipids linked with the choline. Some species of microorganisms possess a lecithinase (also called as phospholipase C), is one of the enzymes which has the ability of split the Phospholipid lecithin, whose activity is used to characterize the several grams positive and the gram-negative bacteria.
The Lecithinase test is commonly performed in the laboratory by preparing a medium and by following certain procedures, which has been discussed below.
Lecithinase Test Objective
The main of the test is to determine the ability of the micro-organism to synthesize the enzyme named lecithinase.
To detect the species of bacteria which is capable of producing a lecithinase enzyme.
Lecithinase Test Principle
Egg yolk agar is one of the enriched medium that is used commonly in many of the laboratories for isolating the characterising the different species of bacteria on the basis of their lecithinase activity. Lecithin is one of the normal components of the egg yolk. In egg yolk agar, the lipoprotein component lecithovitellin which has a capability to split the enzyme lecithinase into phosphorylcholine and an insoluble diglyceride, which results in the formation of the precipitate in the culture medium. Such micro-organisms which possess an enzyme lecithinase breaks down the lecithin to insoluble diglyceride and the phosphorylcholine, that results in the white opaque precipitation which further spreads beyond the edges of the colony. Thus, such opaque zone of precipitation across the colony when it is grown on the yolk agar medium indicates the positive reaction of the lecithinase activity of the organism present in the medium.
Lecithinase Test Reagents
Egg yolk agar
Composition of Media:
|Pancreatic digest of casein||15.0|
|Papaic Digest of a soya bean meal||5.0|
|Egg Yolk emulsion||100.0|
Lecithinase Test Procedure
Initially, a loopful of the test organism is taken and it is streaked as a straight line on the culture plate.
Then the medium is incubated aerobically in the gas pak jar immediately after streaking and it is further transferred into the incubator at a temperature of about 35 to 37ºC. For anaerobes, it is incubated for about 24 to 48 hours, and for aerobes the plate is incubated for 24 to 48 hours.
After incubation, the plate is examined or observed for formation of the opalescent halo surrounding in the inoculum plate.
Lecithinase Test Results
Lecithinase Test Positive Results: If the results of the test are positive, then there will be an appearance of a white opaque and diffused zone which extends along the medium and the surrounding colonies.
Negative Lecithinase Test Results: In case, if the results are negative, there will be absence of an opaque or a white zone that extends along the edges of the colony.
Lecithinase Test Uses
Bacterial lecithinases are considered as one of the special interests as these have their possible role in performing their pathogenicity.
This test also plays a vital role in identification of species like Clostridium perfinges, Pseudomonas aeruginosa, Staphylococcus aureus.
However, the enzymatic activity of the Staphylococcus aureus is greatly used in detecting the coagulase positive strains as they show a high link between the lecithinase activity and the coagulase activity.
This test can also be widely used in differentiating the certain species within the same genus of the Bacillus.
Lecithinase Test Citations