Thursday, October 22, 2009

20 - Nagler's Reaction

At least 12 different toxins have been identified in strains of Cl. perfringens. One of these is the alpha-toxin, a lecithinase that hydrolyses the phospholipid lecithin (a component of cell membranes) to a diglyceride and phosphorylcholine.

The activity of the alpha-toxin can be demonstrated by growth on agar containing egg yolk (as a source of lecithin): an opaque zone representing insoluble diglyceride, becomes evident around colonies of Clostridium perfringens (the Nagler reaction). The activity of alpha-toxin is inhibited by anti-alpha-toxin antibody (generated by vaccination with alpha-toxoid).

The photograph provided above shows a nutrient agar plate enriched with egg yolk. Anti a-toxin was spread over half of the plate (left half) and a heavy inocula of Cl. perfringens and Cl. sporogenes were streaked across the plate at right angles to the anti alpha-toxin boundary.

Note the opaque zone on the upper right half, around the colonies of clostridium perfringens, due to insoluble diglyceride formed as a result of action of lecithinase (alpha toxin) on the lecithin of egg. THIS IS THE NAGLER'S REACTION.

The upper left half does not show this phenomenon because of presence of anti alpha toxin .antibodies.

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