Clinical Laboratory Science Microbiology Practice Test 2026 – The All-In-One Guide to Exam Success!

The hallmark being tested is the distinctive kidney-bean shaped Gram-negative diplococci produced by Neisseria meningitidis. In stained specimens, these bacteria appear as paired cocci with a bean-like appearance, a classic description for Neisseria species. This shape and arrangement set them apart from the other organisms listed: Yersinia pestis is a small Gram-negative rod that often shows bipolar staining rather than a kidney-bean diplococcus; Bartonella species are tiny Gram-negative coccobacilli, often intracellular and not diplococcus-shaped; Actinobacter spp are Gram-positive rods, not Gram-negative diplococci. So the kidney-bean diplococcus points to Neisseria meningitidis.