A throat swab from a suspected case of pharyngeal diphtheria is inoculated onto Loeffler serum slope. After staining the growth with Albert stain, the finding that supports Corynebacterium diphtheriae is:

• A Gram-negative bacilli with bipolar metachromatic granules staining bluish black
• B Gram-positive bacilli with terminal round spores swelling the end of the cell
• C Gram-positive cocci in chains surrounded by a clear halo
• D Gram-positive bacilli with volutin granules appearing bluish black against a green bacillary body ✓

Explanation

On Loeffler serum slope, Corynebacterium diphtheriae shows club-shaped Gram-positive bacilli arranged in Chinese letter or V-L patterns. Albert stain demonstrates polymetaphosphate (volutin) granules as bluish black bodies against the green-stained bacillary body, the defining metachromatic appearance. Terminal spores describe Clostridium tetani, and bipolar granule staining is a feature of other bacteria such as Yersinia.

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.