A 34-year-old technologist presents with mild fever and malaise, with significant edema and notable ulcer. A tissue sample was cultured. BAP shows large, white, ground-glass-like colonies; Gram stain shows boxcar Gram-positive bacilli; Motility is non-motile. Which organism is suspected?

Prepare for the CAMLPR Microbiology Test. Utilize flashcards and engaging multiple-choice questions, each equipped with descriptions and explanations. Ready yourself for an excellent performance!

The pattern points to Bacillus anthracis. The clinical picture of a painless ulcer with significant surrounding edema fits cutaneous anthrax, and the lab clues reinforce that. Bacillus anthracis grows as large, white, ground-glass–like colonies on blood agar and appears as boxcar-shaped Gram-positive bacilli that are non-motile. The non-motility helps distinguish it from other Bacillus species (like B. cereus or B. subtilis, which are typically motile) and from Listeria monocytogenes, which is usually motile and has different colony and presentation features. Put together, the combination of lesion type, colony morphology, and absence of motility makes Bacillus anthracis the most likely organism.