Which of the following is a distinguishing feature of Escherichia coli among members of the bacterial world?

• A. It is a Gram-positive, cocci-shaped bacterium that forms endospores.
• B. It is a Gram-negative, rod-shaped bacterium commonly found in the intestines of humans and animals.
• C. It is a photosynthetic bacterium that produces oxygen.
• D. It is an obligate anaerobe that causes tuberculosis.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the basic characteristics of Escherichia coli (E. coli). It is important to know its Gram stain reaction, shape, and typical habitat.
2. Step 2: Recall that E. coli is a Gram-negative bacterium, which means it does not retain the crystal violet stain during Gram staining and appears pink/red under a microscope.
3. Step 3: Recognize that E. coli is rod-shaped (bacillus), not cocci (spherical) or any other shape.
4. Step 4: Identify the natural habitat of E. coli, which is commonly the intestines of humans and animals, making it part of the normal gut flora.
5. Step 5: Compare these features with the other options: it is not Gram-positive, does not form endospores, is not photosynthetic, and is not an obligate anaerobe causing tuberculosis. This confirms the distinguishing feature of E. coli.