Which of the following organisms is known to be oxidase-positive?

The identification of oxidase-positive organisms is critical in bacteriology, as it helps distinguish between different groups of bacteria based on their metabolic characteristics. In this context, both Aeromonas hydrophila and Vibrio cholerae are known to produce the enzyme cytochrome oxidase, which can be detected using an oxidase test.

Aeromonas hydrophila is a waterborne organism often associated with various infections, and its oxidase-positive status can help differentiate it from other non-fermenting Gram-negative rods. Vibrio cholerae, the causative agent of cholera, is also oxidase-positive and typically found in aquatic environments, further supporting its classified group.

In contrast, Yersinia enterocolitica is known to be oxidase-negative, which is a key feature that can help distinguish it from the aforementioned organisms. Therefore, the recognition of Aeromonas hydrophila and Vibrio cholerae as oxidase-positive is what makes the combined option the correct choice in this question.