A throat smear from a child with membranous pharyngitis is stained using Albert's stain (toluidine blue and malachite green with iodine). Which structure does this stain specifically demonstrate?

• A Bacterial capsules
• B Acid-fast bacilli
• C Metachromatic granules ✓
• D Peritrichous flagella

Explanation

Albert's stain demonstrates the metachromatic (volutin) granules of Corynebacterium diphtheriae. These granules are polymetaphosphate reserves that stain bluish black against the green-stained cytoplasm because their affinity for the dye differs from the rest of the protoplasm. Acid fastness requires carbol fuchsin based stains such as Ziehl-Neelsen, capsules require India ink or Maneval's stain, and flagella require special stains such as Leifson's or Ryu's, so none of these fits the reagent described.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.