**Core Concept**
Clostridia are a group of anaerobic, Gram-positive bacteria that can be classified based on their metabolic activities. Saccharolytic Clostridia are those that break down carbohydrates for energy, whereas proteolytic Clostridia break down proteins.

**Why the Correct Answer is Right**
Among the Clostridia species, those that are saccharolytic include Clostridium perfringens (previously known as Clostridium welchii), which is a major cause of gas gangrene and food poisoning. This organism produces a range of toxins, including alpha-toxin, which is a phospholipase C that breaks down phospholipids in cell membranes. The saccharolytic activity of Clostridium perfringens is due to its ability to ferment various sugars, including glucose, lactose, and sucrose.

**Why Each Wrong Option is Incorrect**
* **Option A:** Clostridium difficile is primarily proteolytic, producing toxins that cause colitis and pseudomembranous colitis. It breaks down proteins in the intestinal mucosa, leading to the characteristic pseudomembrane formation.
* **Option B:** Clostridium tetani is a spore-forming, saccharolytic bacterium that is the causative agent of tetanus. However, this option is incorrect because Clostridium tetani is indeed saccharolytic, not the exception.
* **Option D:** Clostridium septicum is a saccharolytic bacterium that can cause gas gangrene, particularly in the context of malignancy or trauma. It is not the correct answer because it is indeed saccharolytic.

**Clinical Pearl / High-Yield Fact**
When differentiating between Clostridium species, it is essential to remember that proteolytic Clostridia, such as C. difficile, tend to cause disease in the context of disruption of the normal intestinal flora, whereas saccharolytic Clostridia, such as C. perfringens, can cause disease through toxin production and direct tissue damage.

**Correct Answer: C. Clostridium difficile.**