Which organism presents as Gram-negative diplococci with kidney bean shape and is associated with otitis media in adults, often testing positive for butyrate esterase?

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!

Grasping the distinctive combination of shape, clinical context, and a specific biochemical marker helps identify this organism. Moraxella catarrhalis forms Gram-negative diplococci with a kidney-bean shape, a classic description you’ll memorize for these bacteria. In adults, it’s a common culprit in otitis media and sinusitis, so the clinical setting fits well. A key diagnostic clue is that this organism tests positive for butyrate esterase, a rapid test that helps distinguish it from Neisseria species, which are also Gram-negative diplococci but typically do not show butyrate esterase activity and have different disease associations. Haemophilus influenzae would appear as small Gram-negative coccobacilli, not diplococci, and Streptococcus pneumoniae is Gram-positive, not Gram-negative. So the combination of kidney-bean shaped Gram-negative diplococci causing otitis media in adults and positive butyrate esterase points to Moraxella catarrhalis.