Quellung Reaction

**Semantic type:** Laboratory Procedure

**Definition:** A microbiological technique in which bacterial cells are mixed with type-specific antisera, causing the bacterial capsule to swell and become more visible under a microscope. The reaction is based on the binding of antibodies to the polysaccharide capsule, resulting in a characteristic change in refractivity that allows identification and serotyping of encapsulated bacteria.

**Synonyms:** - Neufeld Reaction - QUELLUNG REACTION