Final answer:
A widened mediastinum on a chest X-ray and severe respiratory distress following inhalational exposure typically indicate inhalation anthrax, caused by Bacillus anthracis.
Step-by-step explanation:
The bioterrorism agent that can be identified by a widened mediastinum on a chest X-ray and severe respiratory distress following inhalational exposure is Bacillus anthracis, which causes inhalation anthrax. Inhalation anthrax is the most serious form of the disease and is characterized by symptoms including high fever, difficulty breathing, and chest pains, resembling those of a heart attack. Detection of a widened mediastinum, pleural effusion, respiratory failure, and the presence of gram-positive, rod-shaped bacteria in blood or cerebrospinal fluid samples supports a diagnosis of inhalation anthrax. Confirmation of exposure to B. anthracis and the subsequent need for aggressive antibiotic treatment and supportive care are critical to managing the condition, given its potential to lead to multi-organ failure and death.