A 28-year-old woman from Delhi presents with acute meningitis. CSF analysis shows pleocytosis with predominantly neutrophils, elevated protein (120 mg/dL), and low glucose (25 mg/dL). Gram stain reveals gram-negative diplococci. All of the following are true regarding Neisseria meningitidis EXCEPT:

Explanation

## N. meningitidis Virulence Factors and Distinguishing Features **Key Point:** Neisseria meningitidis DOES possess opacity proteins (Opa and Opc proteins), contrary to what option B states. These surface proteins are involved in adhesion to and invasion of host epithelial and endothelial cells. The claim that N. meningitidis "lacks opacity proteins unlike N. gonorrhoeae" is factually incorrect — both Neisseria species express opacity proteins, making option B the FALSE statement. ### Virulence Factors of N. meningitidis | Factor | Role | Clinical Significance | |--------|------|----------------------| | **Polysaccharide Capsule** | Inhibits complement deposition and phagocytosis; basis for conjugate vaccines (MenACWY, MenB) | Primary virulence factor | | **Lipopolysaccharide (LPS)** | Endotoxin; triggers TLR4 → inflammatory cascade → meningeal inflammation, sepsis | Mediates systemic toxicity | | **IgA Protease** | Cleaves secretory IgA; enables mucosal colonization | Mucosal immune evasion | | **Opacity Proteins (Opa/Opc)** | Present in BOTH N. meningitidis AND N. gonorrhoeae; mediate adhesion and invasion of host cells | NOT exclusive to gonorrhoeae | ### Why Each Option is TRUE (and thus NOT the answer): - **Option A (True):** Penicillin resistance in N. meningitidis is indeed mediated by altered penicillin-binding proteins (PBPs) via chromosomal mutations, resulting in intermediate resistance (MIC 0.1–1 µg/mL). This is a well-established mechanism per Mandell's Principles of Infectious Diseases. - **Option C (True):** LPS endotoxin of N. meningitidis activates TLR4, triggering the inflammatory cascade (TNF-α, IL-1, IL-6) leading to meningeal inflammation and septic shock — a cornerstone of meningococcal pathophysiology (Harrison's 21e, Ch. 297). - **Option D (True):** The polysaccharide capsule is the primary virulence factor, enabling immune evasion, and forms the basis of meningococcal vaccines (serogroups A, C, W, Y, and B) — well established in Ananthanarayan & Paniker's Textbook of Microbiology. **High-Yield:** Option B is FALSE because N. meningitidis expresses Opa (opacity-associated) and Opc proteins that facilitate attachment to and invasion of nasopharyngeal epithelium and blood-brain barrier endothelium. These proteins are shared with N. gonorrhoeae and are NOT absent in meningococci. **Clinical Pearl:** The polysaccharide capsule distinguishes N. meningitidis from N. gonorrhoeae (which is non-encapsulated). Both species share IgA protease production and opacity proteins as common virulence mechanisms [Ananthanarayan & Paniker, 10th ed.; Mandell, Douglas & Bennett's Principles of Infectious Diseases, 9th ed.].