What is the most likely identification of a bacterium that exhibits small yellow colonies on blood agar, is a Gram-negative curved fusiform rod, and is catalase positive?

The identification of a bacterium characterized by small yellow colonies on blood agar, a Gram-negative curved fusiform rod morphology, and a catalase positive reaction strongly indicates Capnocytophaga canimorsus.

Capnocytophaga canimorsus is a part of normal oral flora in dogs and cats, and its morphology aligns with the description of being a curved, fusiform rod. The small yellow colonies on blood agar can be attributed to its growth characteristics, and its catalase-positive nature helps in differentiating it from other similar bacteria.

Understanding why this organism fits the description is important. Capnocytophaga canimorsus is particularly associated with infections in humans who have close contact with pets, and the identification based on its distinct growth and biochemical properties is essential in clinical microbiology.

The other organisms listed have different characteristics; for instance, Francisella tularensis is known for its small, non-pigmented colonies and more specific growth conditions. Legionella pneumophila typically exhibits a different colony morphology and has specific growth requirements that do not align with the description given. Pseudomonas aeruginosa, while it can produce various colony colors on media, typically forms larger colonies and is also associated with different clinical