Elek's test

Elek's test, also known as the immunodiffusion technique, is an in vitro virulence test performed upon Corynebacterium diphtheriae.[1] It is used to test for toxigenicity of C. diphtheriae.

It was characterized in 1949 by American microbiologist Stephen Dyonis Elek (1914–1992).[2] A strip of filter paper impregnated with diphtheria antitoxin is buried just beneath the surface of a special agar plate before the agar hardens. Strains to be tested are streaked with known positive and known negative toxigenic strains on the agar's surface in a line across the plate, and at a right angle to the antitoxin paper strip.

After incubation for 24 hours at 37 degrees Celsius, plates are examined with transmitted light for the presence of fine precipitin lines at a 45-degree angle to the streaks. The presence of precipitin lines indicates that the strain produced toxin that reacted with the antitoxin.