A fastidious, oxidase-positive, Gram-negative cocci from a rectal swab is likely which organism?

The identification of a fastidious, oxidase-positive, Gram-negative cocci from a rectal swab points strongly towards Neisseria gonorrhoeae. This organism is known for being fastidious, meaning it requires specific growth factors or environmental conditions for culture, which aligns with the description provided.

Neisseria gonorrhoeae is also oxidase-positive, distinguishing it from many other Gram-negative bacteria. Being oxidase-positive indicates the presence of the enzyme cytochrome c oxidase, which is a characteristic of certain bacteria, including the Neisseria species.

The rectal swab is particularly relevant, as Neisseria gonorrhoeae can be isolated from extragenital sites such as the rectum, especially in sexually active individuals.

In contrast, Escherichia coli is not a fastidious organism and is lactose fermenting, typically resulting in a different profile in culture. While Neisseria meningitidis is also an oxidase-positive Gram-negative cocci, it is primarily associated with other specimen types such as cerebrospinal fluid and respiratory tract samples and is less frequently found in rectal swabs. Staphylococcus aureus is a Gram-positive cocci and would not match the Gram-negative requirement.