Which genus may occasionally exhibit kidney bean-shaped diplococci morphology?

Which genus may occasionally exhibit kidney bean-shaped diplococci morphology?

• A. Moraxella
• B. Escherichia
• C. Klebsiella
• D. Vibrio

Answer: (A)

The shape described—kidney bean–shaped diplococci in pairs—fits Gram-negative cocci arranged in pairs. Moraxella catarrhalis is known to appear as diplococci with that coffee-bean/kidney-bean morphology. It’s a Gram-negative, oxidase-positive coccus that can resemble Neisseria on stains, which is why this morphology is noted for this genus. The other choices are not typically diplococci: Escherichia and Klebsiella are Gram-negative rods, and Vibrio are curved rods. So Moraxella is the genus that may occasionally show kidney bean–shaped diplococci.

The shape described—kidney bean–shaped diplococci in pairs—fits Gram-negative cocci arranged in pairs. Moraxella catarrhalis is known to appear as diplococci with that coffee-bean/kidney-bean morphology. It’s a Gram-negative, oxidase-positive coccus that can resemble Neisseria on stains, which is why this morphology is noted for this genus. The other choices are not typically diplococci: Escherichia and Klebsiella are Gram-negative rods, and Vibrio are curved rods. So Moraxella is the genus that may occasionally show kidney bean–shaped diplococci.