Which one of the following shows if a clinical isolate of Corynebacterium diphtheriae is toxigenic?
Q. Bacterial agglutination with specific antisera
R. Colonial morphology on blood tellurite medium
S. Positive Elek plate
T. Positive identification of “gravis” strain
U. Positive Schick test.
The correct answer is S. Positive Elek plate.
The Elek test is used to determine if a clinical isolate of Corynebacterium diphtheriae produces diphtheria toxin. The test involves inoculating a culture plate with the isolate and specific antitoxin. If the bacteria produce toxin, a precipitin line will form where the antitoxin and toxin meet, indicating toxigenicity.