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
Frequently asked questions
What is Quellung reaction?
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.
What is the high-yield clue for Quellung reaction?
Apparent capsular 'swelling' after adding specific antiserum is the classic Quellung clue for encapsulated pneumococcus.
What is Quellung reaction associated with?
Quellung reaction is associated with Streptococcus pneumoniae serotyping association; Also Klebsiella, Neisseria, and Haemophilus capsules; Capsule as virulence factor framing.
What is Quellung reaction commonly confused with?
Quellung reaction is commonly confused with India ink preparation and Latex agglutination.
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.