Harr Microbiology Practice Test

The identification of a nonmotile gram-negative coccobacillus from cerebrospinal fluid (CSF) that is positive for indophenol oxidase leads to the conclusion that Moraxella lacunata is the most likely organism.

Moraxella lacunata is recognized for having a predominantly coccobacillus morphology and is part of the normal flora of the upper respiratory tract but can occasionally cause opportunistic infections, especially in immunocompromised individuals. Its ability to produce indophenol oxidase indicates a metabolic characteristic that is aligned with this organism and helps distinguish it from other species.

In contrast, other options have differing characteristics. Acinetobacter spp. can also be coccobacilli, but they are more commonly associated with infections in ventilated patients and are known to be oxidase-negative. Pseudomonas aeruginosa, while it can be motile and also gram-negative, typically presents as a rod, not a coccobacillus, and is oxidase-positive. Pseudomonas stutzeri is another rod-shaped organism that is motile and primarily associated with soil and water.

These contrasting features further emphasize that Moraxella lacunata is the most probable identification based on