In the laboratory confirmation of diphtheria, smears from colonies on Loeffler serum slope are stained by Albert stain. A positive result shows:
- A Purple bacilli with pink bipolar bodies resembling safety pins
- B Green bacilli with bluish-black metachromatic granules at the poles ✓
- C Red bacilli retaining carbol fuchsin against acid decolorisation
- D Colourless bacilli on a purple background with beaded granules
Correct answer: B. Green bacilli with bluish-black metachromatic granules at the poles
Explanation
Albert stain uses toluidine blue and malachite green. The body of Corynebacterium diphtheriae stains green while the polymetaphosphate (volutin) granules take up the blue dye and appear bluish-black, showing metachromasia. Safety pin bipolar staining with Wayson or methylene blue suggests Yersinia pestis, killing option A. Acid fastness defines mycobacteria, and option D describes the Ziehl-Neelsen appearance. Metachromatic granules are best demonstrated on Loeffler serum slope cultures after 6 to 12 hours.
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.