Which organism is identified as a curved, gram-negative rod that is nonfermentive, nitrate-positive, and microaerophilic?

The organism identified as a curved, gram-negative rod that is nonfermentive, nitrate-positive, and microaerophilic is indeed Campylobacter jejuni. This bacterium is well-known for its characteristic spiral or curved shape and is commonly associated with gastrointestinal infections, particularly gastroenteritis, often linked to the consumption of undercooked poultry and contaminated water.

Campylobacter jejuni requires a reduced oxygen environment to grow effectively, which is described as microaerophilic; it thrives in conditions where oxygen is available but at lower levels than what is found in the atmosphere. Additionally, this bacterium is capable of reducing nitrate to nitrite, a notable biochemical reaction that serves as a differentiating factor from other bacteria.

This combination of features—curved morphology, gram-negative status, nonfermentative metabolism, and microaerophilic growth requirements—uniquely identify Campylobacter jejuni among the provided choices. Other organisms listed may possess some similar characteristics but do not match all criteria, making Campylobacter the correct answer for this question.