**Core Concept**
Pseudomembranous colitis, also known as Clostridioides difficile (C. difficile) infection, is a type of infectious diarrhea caused by the Clostridioides difficile bacteria. The condition often results from the use of broad-spectrum antibiotics that disrupt the normal gut flora, leading to overgrowth of C. difficile. Treatment typically involves antibiotics aimed at eradicating the causative bacteria.

**Why the Correct Answer is Right**
Streptogramins, a class of antibiotics that inhibit protein synthesis, are not typically used to treat C. difficile infection. This is because streptogramins are generally ineffective against anaerobic bacteria like C. difficile. In contrast, other antibiotics such as metronidazole and vancomycin are effective against anaerobic bacteria and are commonly used to treat C. difficile infection. Fidaxomycin is also used for C. difficile treatment, particularly in cases of metronidazole or vancomycin failure.

**Why Each Wrong Option is Incorrect**
**Option A:** Metronidazole is a nitroimidazole antibiotic that is effective against anaerobic bacteria, including C. difficile, making it a suitable treatment option.
**Option B:** Vancomycin is a glycopeptide antibiotic that is also effective against C. difficile, particularly in severe cases or when metronidazole is contraindicated.
**Option C:** Fidaxomycin is a macrolide antibiotic that is specifically used to treat C. difficile infection, particularly in cases of metronidazole or vancomycin failure.

**Clinical Pearl / High-Yield Fact**
When treating C. difficile infection, it is essential to choose an antibiotic that is effective against anaerobic bacteria, such as metronidazole, vancomycin, or fidaxomycin. The choice of antibiotic may depend on the severity of the infection, patient comorbidities, and previous treatment failures.

**✓ Correct Answer: D. Streptogramins**