Brachyspira spp are best described as which type of organism?

• A. Gram-negative diplococcus
• B. Gram-positive cocci
• C. Gram-negative spirochete, motile and anaerobic
• D. Gram-variable rod

Answer: (C)

Brachyspira species are spiral-shaped bacteria known as spirochetes. They move with a corkscrew motion thanks to axial filaments that lie between their membranes. They have a Gram-negative cell envelope, reflecting an outer membrane with a thin peptidoglycan layer, and they grow best in anaerobic conditions, being motile and anaerobic. Put together, the description that fits best is a Gram-negative spirochete that is motile and anaerobic. The other descriptions don’t match the shape or lifestyle—diplococci or cocci describe round cells, and a Gram-variable rod doesn’t capture the characteristic spiral, motility, and anaerobic growth of Brachyspira.