Brucella species are best described as which morphological type?

• A. Gram-negative cocci in clusters
• B. Gram-negative coccobacilli
• C. Gram-positive cocci
• D. Gram-negative spirilla

Answer: (B)

Brucella species are best described as Gram-negative coccobacilli. Their cells are small and short, showing a shape between cocci and bacilli, which is captured by the term coccobacillus. They stain pink/red with Gram stain because of their thin peptidoglycan layer and outer membrane. In specimens, they often appear as tiny, barely rod-shaped forms and can be seen inside macrophages due to their facultative intracellular lifestyle. This morphology distinguishes them from Gram-negative cocci in clusters (which are cocci like Staphylococcus), Gram-positive cocci (which stain purple and are truly cocci), and Gram-negative spirilla (which are curved rod-shaped bacteria like Campylobacter).