**Question:** All are capsulated bacteria except-

A. Escherichia coli (E. coli)
B. Staphylococcus aureus
C. Streptococcus pneumoniae
D. Haemophilus influenzae

**Core Concept:** Capsules are polysaccharide coatings that bacteria may have, which can influence their virulence, adhesion, and evasion from the host's immune system.

**Why the Correct Answer is Right:** Escherichia coli (E. coli) is a non-pathogenic gut bacterium, which does not require a capsule for survival or virulence in the human body. In contrast, pathogenic bacteria like Streptococcus pneumoniae (pneumococcus) and Haemophilus influenzae (non-typeable H. influenzae) produce polysaccharide capsules that aid in their virulence, adhesion, and immune evasion.

**Why Each Wrong Option is Incorrect:**

B. Staphylococcus aureus is a pathogenic bacterium and does produce a capsule (coatings), but the question specifically mentions "all are capsulated bacteria except" which refers to the correct answer.

B. Haemophilus influenzae (typeable H. influenzae) also produces a capsule, but the focus is on the non-typeable strain which does not have a capsule.

**Why Option A is Incorrect:**
Escherichia coli (E. coli) is a commensal bacterium found in the human gastrointestinal tract and does not require a capsule for survival or virulence.

**Why Option B is Incorrect:**
Staphylococcus aureus is a pathogenic bacterium and does produce a capsule (coatings), but the question specifically mentions "all are capsulated bacteria except" which refers to the correct answer.

**Why Option C is Incorrect:**
Haemophilus influenzae (typeable H. influenzae) also produces a capsule, but the focus is on the non-typeable strain which does not have a capsule.

**Why Option D is Incorrect:**
Haemophilus influenzae (non-typeable H. influenzae) does not have a capsule and is therefore considered "capsulated bacteria-free."

**Why Option E is Incorrect:**
Enterococcus faecalis is a commensal bacterium found in the gastrointestinal tract and does not require a capsule for survival or virulence.

**Clinical Pearl:**
Understanding the role of bacterial capsules in virulence and immune evasion can guide in clinical decision making when considering antibiotic treatment choices, as some bacteria with capsules may be resistant to certain antibiotics that target cell wall synthesis or protein synthesis. This understanding helps in choosing the appropriate antibiotic therapy considering the bacterial species and its virulence factors.