**Core Concept**
Bacillus anthracis is a gram-positive, rod-shaped bacterium that causes anthrax, a zoonotic disease primarily affecting animals but can also infect humans. It is a spore-forming bacterium, meaning it can survive in a dormant state for extended periods.

**Why the Correct Answer is Right**
The correct answer is related to the pathogenesis of Bacillus anthracis. When inhaled, B. anthracis spores are phagocytosed by macrophages in the lungs, where they germinate into vegetative cells. These cells then produce toxins, including the lethal factor, edema factor, and protective antigen, which cause the characteristic symptoms of anthrax, such as edema, hemorrhage, and eventually death. The protective antigen is crucial as it forms a complex with the lethal factor and edema factor, allowing them to enter the host cell.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the pathogenesis of B. anthracis. While the spores are indeed phagocytosed by macrophages, the subsequent germination and toxin production are critical to the disease process.
**Option B:** This option is incorrect as it is not specific to B. anthracis. Many bacteria can cause septicemia, but this option does not highlight the unique characteristics of B. anthracis.
**Option C:** This option is incorrect as it is not directly related to the pathogenesis of B. anthracis. While antibiotics can be used to treat anthrax, this option does not accurately describe the disease process.

**Clinical Pearl / High-Yield Fact**
Bacillus anthracis is a classic example of a bacterium that can be used as a bioterrorism agent due to its ease of production and dissemination. Its spore-forming ability allows it to survive for extended periods, making it a highly virulent and potentially deadly pathogen.

**Correct Answer: D.**