Which genus is most commonly described as having kidney bean-shaped Gram-negative diplococci?

• A. Neisseria meningitidis
• B. Yersinia pestis
• C. Bartonella spp.
• D. Actinobacter spp.

Answer: (A)

The main idea here is the distinctive cell arrangement and shape of certain Gram-negative bacteria. Neisseria species are classic for appearing as paired cocci (diplococci) that, when viewed together, resemble a kidney bean. This kidney-bean shaped diplococcus description is a well-known way microbiology texts summarize the appearance of Neisseria under the Gram stain, especially in samples from infections like meningitis or gonorrhea, where the organisms are often seen inside neutrophils.

In contrast, the other organisms listed do not match this morphology. Yersinia pestis is a rod-shaped Gram-negative bacillus; Bartonella species are small Gram-negative coccobacilli or pleomorphic rods; Actinobacteria are typically Gram-positive and not described as kidney bean-shaped diplococci. Therefore, Neisseria is the genus most commonly described with kidney bean-shaped Gram-negative diplococci.