Pleomorphic gram-positive bacilli with a palisade arrangement resembling Chinese characters are most characteristic of which genus?

• A. Bacillus anthracis
• B. Listeria monocytogenes
• C. Corynebacterium pseudodiphtheriticum
• D. Bacillus subtilis

Answer: (C)

Recognizing pleomorphic gram-positive bacilli that arrange in palisades forming angular, “Chinese character” patterns points to Corynebacterium. These bacteria divide in one plane and remain attached at an angle, creating the distinctive, stacked appearance often described as Chinese letters on Gram stain. This palisading pattern is a hallmark of Corynebacterium species, including non-diphtherial ones like Corynebacterium pseudodiphtheriticum.

In contrast, Bacillus species typically appear as long, uniform rods and form spores, not the zigzag palisade pattern. Listeria monocytogenes are small gram-positive coccobacilli that occur in short chains or singly, not in the characteristic palisades. Therefore, the genus Corynebacterium best fits the described morphology.