All the following are obligate anaerobes except?
**Core Concept**
Obligate anaerobes are microorganisms that require a low-oxygen environment to survive and multiply. They are unable to grow in the presence of oxygen and typically thrive in environments with limited or no oxygen, such as deep wounds, the gastrointestinal tract, or soil.
**Why the Correct Answer is Right**
Obligate anaerobes lack the necessary enzymes to withstand oxidative stress, which would occur in environments with oxygen. They often produce enzymes such as superoxide dismutase to detoxify reactive oxygen species, but this is not sufficient to support growth in the presence of oxygen. Instead, they rely on alternative metabolic pathways, such as fermentation, to generate energy.
**Why Each Wrong Option is Incorrect**
**Option A:** Bacteroides fragilis is an obligate anaerobe commonly found in the human gut. It is a key contributor to the gut microbiome and plays a crucial role in carbohydrate fermentation.
**Option B:** Clostridium difficile is also an obligate anaerobe that can cause severe diarrhea and colitis. It is often associated with antibiotic use and hospital-acquired infections.
**Option C:** Peptostreptococcus anaerobius is a gram-positive, anaerobic bacterium that is commonly found in deep wounds and abscesses.
**Clinical Pearl / High-Yield Fact**
It's essential to note that while obligate anaerobes are difficult to culture in the laboratory, they can be identified using specialized media, such as thioglycollate broth or Schaedler agar.
**Correct Answer: D. Peptostreptococcus anaerobius is an obligate anaerobe.