Lab method
Quellung reaction
Antibody-induced capsular swelling
KVELL-oong
High-yield clue
Apparent capsular 'swelling' after adding specific antiserum is the classic Quellung clue for encapsulated pneumococcus.
Overview
A capsule-visualization concept in which type-specific anticapsular antibody binds a bacterium's polysaccharide capsule, making it appear swollen and sharply outlined under the microscope.
Classification
- Immunologic capsule reaction
- Serotyping concept
- Light microscopy
- Neufeld reaction synonym
Lab & identification clues
- Capsule looks enlarged and refractile
- Type-specific antisera define serotype
- Gold-standard pneumococcal serotyping vocabulary
- Also applies to other encapsulated bacteria
Associations
- Streptococcus pneumoniae serotyping association
- Also Klebsiella, Neisseria, and Haemophilus capsules
- Capsule as virulence factor framing
Commonly confused with
- India ink preparation
- Latex agglutination
Your notes
Original concept summary for coursework. Sources checked: OpenStax Microbiology 2e and NCBI Bookshelf Medical Microbiology; reviewed 2026-06. Describes vocabulary and interpretation concepts only; not a lab protocol and not for handling specimens or identifying patient isolates.