The Quellung reaction, historically used for typing isolates of Streptococcus pneumoniae, depends on which property of the organism?
- A Agglutination of pili by anticapsular antibodies
- B Capsular swelling due to binding of the autolysin LytA
- C Swelling of the polysaccharide capsule on exposure to type-specific antiserum ✓
- D Precipitation of capsular antigen with cell wall C polysaccharide
Correct answer: C. Swelling of the polysaccharide capsule on exposure to type-specific antiserum
Explanation
The Neufeld Quellung reaction occurs when type-specific anticapsular antibody binds the pneumococcal polysaccharide capsule, making it appear swollen and refractile under the microscope. More than 90 capsular serotypes exist, and typing guided both epidemiology and conjugate vaccine design such as PCV covering prevalent serotypes. LytA mediates autolysis in bile solubility, not capsular swelling, so option B is wrong. Pneumococci have no pili-based agglutination reaction of this kind.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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