Sputum from a patient with lobar pneumonia is mixed with type-specific pneumococcal antiserum on a slide. Under the microscope, the bacterial capsule appears swollen, sharply demarcated and more refractile than in the untreated control. What is this reaction called?

• A India ink negative staining
• B Neufeld (quellung) reaction ✓
• C Maneval's capsular stain
• D Agglutination of O somatic antigen

Explanation

The quellung reaction, described by Neufeld, is the microscopic swelling and increased refractility of the pneumococcal capsule when it combines with homologous type-specific anticapsular antibody. It was classically used for rapid typing of Streptococcus pneumoniae in sputum. India ink merely outlines the capsule as a clear halo against a dark background without any antibody, Maneval's is a chemical capsular stain again involving no antiserum, and agglutination of somatic O antigen applies to Gram-negative enteric bacilli, not the polysaccharide capsule of the pneumococcus.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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