Albert's stain (metachromatic granules)

Principle

Corynebacterium diphtheriae stores polyphosphate (volutin) granules. With toluidine blue and malachite green, the granules stain blue-black and the bacilli green, helping presumptive identification.

Reagents

• Albert's stain (toluidine blue and malachite green in acetic acid and alcohol)
• Albert's iodine

Procedure

• Fix the smear; apply Albert's stain for 3–5 minutes.
• Drain without washing; apply iodine for 1–2 minutes.
• Wash, blot dry and examine under oil immersion.

Results

• Bacilli green; granules blue-black, often at the poles
• Arrangement like Chinese letters or palisades

Note

Granules are not specific; diagnosis needs culture (tellurite medium) and a toxin test (Elek or PCR for the tox gene).