**Core Concept**
Neisseria meningitidis is a Gram-negative diplococcus that causes epidemic meningitis, particularly in adolescents and young adults. It is a leading cause of bacterial meningitis in this age group, often resulting in severe outcomes if not treated promptly.

**Why the Correct Answer is Right**
Neisseria meningitidis is highly virulent and can cause rapid progression to severe meningitis. The bacteria produce a polysaccharide capsule that evades host immune response, allowing it to cause severe disease. The capsule is also responsible for the organism's ability to cause invasive disease, including meningitis and septicemia.

**Why Each Wrong Option is Incorrect**
**Option A:** Haemophilus influenzae type b (Hib) is a Gram-negative coccobacillus that can cause meningitis, but it is more common in young children, not adolescents. Hib meningitis is often preceded by otitis media or sinusitis.

**Option B:** Streptococcus pneumoniae is a Gram-positive diplococcus that can cause meningitis, especially in older adults and those with underlying medical conditions. However, it is less common in adolescents.

**Option C:** Escherichia coli (E. coli) is a Gram-negative rod that can cause meningitis, particularly in neonates and those with underlying medical conditions. E. coli meningitis is often associated with specific risk factors, such as central nervous system shunts.

**Option D:** Listeria monocytogenes is a Gram-positive rod that can cause meningitis, particularly in pregnant women, the elderly, and those with weakened immune systems.

**Clinical Pearl / High-Yield Fact**
Neisseria meningitidis meningitis can progress rapidly to severe disease, often requiring prompt treatment with antibiotics, such as ceftriaxone. Vaccination against N. meningitidis is recommended for adolescents and young adults, particularly those at high risk, such as college students living in dormitories.

**Correct Answer:** C.