A throat swab from a patient with a grey pseudomembrane grows colonies on tellurite medium showing black metallic colonies. Elek's test is performed. This test detects:
- A Toxigenicity (production of diphtheria toxin) via immunodiffusion ✓
- B The neuraminidase activity of the organism
- C The beta-hemolytic activity of the organism on blood agar
- D Invasiveness by the Sereny test principle
Correct answer: A. Toxigenicity (production of diphtheria toxin) via immunodiffusion
Explanation
Elek's gel diffusion test (immunodiffusion test) detects diphtheria toxin production by Corynebacterium diphtheriae. A filter paper strip impregnated with diphtheria antitoxin is laid on a serum agar plate, and the test strain is streaked perpendicularly to it; toxigenic strains produce a precipitation line of identity with a control toxigenic strain. Tellurite medium (modified Hoyle's or Clauberg's) is used for selective isolation. PCR for tox gene now supplements or replaces Elek's in modern laboratories.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.