Which organism forms large white ground-glass colonies on blood agar and appears as boxcar-shaped Gram-positive bacilli that are non-motile?

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This question tests the link between colony appearance on blood agar, Gram-stain shape, and motility to identify Bacillus anthracis. The large white, ground-glass colonies on blood agar are a classic clue for B. anthracis, which tends to form non-hemolytic, gray-white colonies with that characteristic “ground-glass” look. On Gram stain, it appears as boxcar-shaped Gram-positive bacilli, and it is non-motile, which helps distinguish it from other Bacillus species that are motile or show different colony features.

In contrast, organisms like Bacillus cereus are usually motile and can show hemolysis, Listeria monocytogenes can also appear boxcar-shaped but is motile at room temperature (tumbling motility), and Clostridium perfringens is anaerobic and typically shows different colony and hemolysis patterns. The specific combination of large, non-hemolytic, ground-glass colonies with non-motile, boxcar-shaped Gram-positive rods best fits Bacillus anthracis.