Elek's gel precipitation test, historically used to demonstrate toxigenicity of Corynebacterium diphtheriae isolates, belongs to which category of immunological techniques?

• A Complement fixation
• B Passive agglutination
• C Immunodiffusion in gel ✓
• D Immunofluorescence

Explanation

In Elek's test, a filter paper strip soaked in diphtheria antitoxin is incorporated into agar, and the test culture is streaked at right angles. Toxin diffusing from toxigenic strains meets the diffusing antitoxin and forms a visible line of precipitate, typically producing an arrowhead pattern with the known positive control. This is a gel immunodiffusion (precipitation) technique. It involves neither complement, nor particle-bound antigen for agglutination, nor fluorescent labels.

Reference: Ananthanarayan and Paniker Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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