The classic “Chinese letter” (palisade) arrangement on microscopy is characteristic of which bacterium in clinical microbiology?

Introduction / Context:Arrangement and morphology are rapid bench clues in bacteriology. “Chinese letter” or cuneiform arrangements refer to angular groupings of club-shaped rods that help presumptively identify certain organisms before definitive tests return.

Given Data / Assumptions:

• The pattern described is “Chinese letter” (palisading, V or L shapes).
• We compare several Gram-positive rods of clinical relevance.

Concept / Approach:Corynebacterium diphtheriae (and related coryneforms) show club-shaped, pleomorphic rods that align at sharp angles due to snapping division. This yields characteristic V, L, and “Chinese letter” patterns on smears, especially with methylene blue or Albert stain.

Step-by-Step Solution:

Verification / Alternative check:Classic lab teaching emphasizes C. diphtheriae’s metachromatic granules (volutin) and angular arrangements on direct smears or low-complexity cultures.

Why Other Options Are Wrong:

• Bacillus anthracis: forms chains of boxcar rods, not “Chinese letters.”
• Mycobacterium tuberculosis: acid-fast straight/slender rods without palisading.
• Clostridium tetani: terminal spores (“drumstick”), not angular groupings.

Common Pitfalls:Over-reliance on morphology alone; confirm with culture, toxin assays, or PCR for diphtheria.

Final Answer:Corynebacterium diphtheriae